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In Germany, the national gas hydrate programme “Gas Hydrates in the Geosystem” has been initiated in 2000 as part of the new R&D programme GEOTECHNOLOGIES, financed by the Federal Ministry for Education and Research (BMBF) and the German Research Council (DFG). The gas hydrate programme promotes a better understanding of the nature of hydrates, hydrate-bearing sediments, and the interaction between the global methane hydrate reservoir and the world’s oceans and atmosphere. Research projects covering a wide spectrum of science and technology, including geology, biogeochemistry, geophysics, physical chemistry and mechanical engineering. These are carried out in close collaboration between various national and international partners from academia and industry. Field studies are underway at the Cascadia Margin off western North America, in the Black Sea, the Mackenzie Delta of the northwestern Canadian Arctic, and off-shore Central-America and Central-Africa.

This abstract volume contains the presentations given during four topical sessions of the first status seminar “Gas Hydrates in the Geosystem” held at the GEOMAR Research Centre in Kiel, Germany. The abstracts reflect the multidisciplinary approach of the programme and provides an excellent overview of where current gas hydrate research in Germany stands.

Science Report GEOTECHNOLOGIEN

Natural gas hydrates as a potential (i) energy resource, (ii) factor in global climate change and (iii) trigger of submarine geohazard have received wide international attention in the past years.

Gas Hydrates in the Geosystem

Gas Hydrates in the Geosystem

GEOTECHNOLOGIEN Science Report

Gas Hydrates in the Geosystem Status Seminar GEOMAR Research Centre Kiel 6-7 May 2002

Programme & Abstracts

The GEOTECHNOLOGIES programme is financed by the Federal Ministry for Education and Research (BMBF) and the German Research Council (DFG)

No. 1

ISSN: 1619-7399

No. 1

GEOTECHNOLOGIEN Science Report

Gas Hydrates in the Geosystem Status Seminar GEOMAR Research Centre Kiel 6-7 May 2002

Programme & Abstracts

Number 1

No. 1

Impressum

Schriftleitung Dr. Alexander Rudloff Dr. Ludwig Stroink © Koordinierungsbüro GEOTECHNOLOGIEN, Potsdam 2002 ISSN 1619-7399 The Editors and the Publisher can not be held responsible for the opinions expressed and the statements made in the articles published, such responsibility resting with the author.

Die Deutsche Bibliothek – CIP Einheitsaufnahme GEOTECHNOLOGIEN; Gas Hydrates in the Geosystem, Status Seminar, GEOMAR Research Centre Kiel, 6-7 May 2002, Programme & Abstracts – Potsdam: Koordinierungsbüro GEOTECHNOLOGIEN, 2002 (GEOTECHNOLOGIEN Science Report No. 1) ISSN 1619-7399 Bezug / Distribution Koordinierungsbüro GEOTECHNOLOGIEN Telegrafenberg A6 14471 Potsdam, Germany Fon +49 0331-288 10 71 Fax +49 0331-288 10 77 www.geotechnologien.de geotech@gfz-potsdam.de

Preface

Natural gas hydrates have received wide international attention because of their potential effects on human welfare. In Germany a national programme “Gas Hydrates in the Geosystem” was launched in 2000 as part of the new R&D Programme GEOTECHNOLOGIES. Goal of the programme is to improve our basic knowledge concerning the distribution and physical/chemical nature of naturally occurring methane hydrates.

In an initial phase (2000-2003) a total sum of € 15 million will be invested by the Federal Ministry of Education and Research (BMBF) on a balanced portfolio of laboratory and field studies, tool design and testing, and computer model development.

The currently funded investigations focus on four key themes: (i) the quantification of chemical and physical properties of natural gas hydrates, (ii) the carbon cycle and the role of

hydrates in global climate forcing, (iii) the development of new technologies (e.g. seafloor fluid flux measurements), and (iv) as trigger of submarine geohazards.

The main objective of the first status seminar “Gas Hydrates in the Geosystem” is to bring together the national gas hydrate community to present their ongoing work and exchange results; because several projects are interlinked and depend on each other’s progress. We very much welcome further visitors from Europe and overseas to share their results and interests. To all of them, this meeting will provide a lively forum to help define future goals and to stimulate ongoing collaborative efforts.

Ludwig Stroink Erwin Suess

Table of Contents

Scientific Programme ........................... 1 -

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Abstracts of Oral Presentations and Posters (in alphabetical order) ....... 8 - 147 Authors’ Index................................. 148 - 151 Notes

Scientific programme of the status seminar „Gas Hydrates in the Geosystem“ at GEOMAR Research Centre Kiel: Monday, 6 May 2002 10.00 Registration and poster mounting 11.00 – 11.15 Welcome GLOBAL CARBON CIRCLE AND CLIMATE EFFECTS (E. SUESS) 11.15 – 11.30 Boetius A. & MUMM working group: The enigmatic process of anaerobic oxidation of methane: first results of project MUMM 11.30 – 11.45 Kasten S., Hensen C., Schneider R., Spieß V.: Geochemical relicts of gas hydrate dissociation in sediments of pockmark sites of the Congo Fan (CONGO) 11.45 – 12.00 Michaelis W., Seifert R., and the shipboard scientific party of the GHOSTDABS cruise: Structures and processes at methane seeps of the Black Sea (GHOSTDABS) 12.00 – 12.15 Seifert R., Nauhaus K., Thiel V., Blumenberg M., Widdel F., Michaelis W.: Biomarkers and biogeochemical activity in methane fed microbial mats of the Black Sea (GHOSTDABS) 12.15 – 12.30 Bohrmann G. & METEOR 52/1 cruise participants: Mud volcanoes and gas hydrates in the Black Sea – an important linkage to the methane cycle (OMEGA, INGGAS) 12.30 – 12.45 Wallmann K., Bohrmann G., Drews M., Suess E.: Fluid-geochemistry of active mud volcanoes in the Black Sea (OMEGA) 12.45 – 13.00 Haeckel M., Suess E., Wallmann K., Rickert D.: Gas hydrate dynamics – Modelling hydrate formation in near surface sediments 13.00 – 14.00 Lunch break

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14.00 – 14.15 Reichel Th., Halbach P., Holzbecher E.: Tectonically induced migration of the sulfatemethane-reaction zone in marine sediments of the Sea of Marmara - a case study (GHOSTDABS) 14.15 – 14.30 Eisenhauer A., Teichert B.M.A., Bohrmann G., Liebetrau V., Linke P.: Authigenic Carbonates in a Cold Seep Environment: Sensitive Recorders of Rapid Anoxia and Sealevel Changes Determined by U- and Th-isotope Measurements (LOTUS) TECHNOLOGICAL AND METHOLOGICAL DEVELOPMENTS (J. ERZINGER) 14.30 – 14.45 Amann H., Hohnberg H.-J.: Autoclave sampling and in-situ preservation system, status and outlook, March 2002 (OMEGA) 14.45 – 15.00 Linke P., Pfannkuche O., Gust G., Sommer S., Gubsch S., Poser M., Greinert J.: Status of development of long-term observatories for gas hydrate research within the collaborative project LOTUS 15.00 – 15.15 Gubsch S., Viergutz T., Gust G., Müller V., Holscher B.: An in-situ laboratory array for biogeochemical processes under deep sea conditions with and without fluid venting (LOTUS) 15.15 – 15.30 Reston T., Gajewski D., Hübscher C., Flüh E., Bialas J., Villinger H., Theilen Fr., and the INGGAS Group: An Introduction to INGGAS: INtegrated Geophysical characterisation and quantification of GAS hydrates 15.30 – 15.45 Villinger H., Gennerich H.-H., Grevemeyer I., Kaul N.: INGGAS-Flux: New tools for energy and fluid-flux: pore pressure and thermal gradient probes 5.45 – 16.00 Breitzke M., Bialas J., and INGGAS working group: A Deep-Towed Digital Multichannel Seismic Streamer for Very High-Resolution Studies of Marine Subsurface Structures - System Development and First Results of RV Sonne Cruise SO162 (INGGAS Test) 16.00 – 16.30 Coffee break 16.30 – 18.00 Short presentation of the posters 18.00 – 19.15 Poster show approx. 19.30 Dinner in the Kantine of GEOMAR

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Tuesday, 7 May 2002 TECHNOLOGICAL AND METHOLOGICAL DEVELOPMENTS (M. BREITZKE) 08.30 – 08.45 Weber M.H. & the Mallik working group: Mallik 2002: An In-situ Gas Hydrate Laboratory 08.45 – 09.00 Bauer K., Pratt R.G., Weber M.H., Harris J.M., Shimizu S., and the Mallik working group: Crosshole seismic monitoring before and during a gas hydrate stimulation test 09.00 – 09.15 Wiersberg T., Zimmer M., Schicks J., Dahms E., Erzinger J., and the Mallik working group: Real-time mud gas monitoring at Mallik 4L-38 and 5L-38 wells 09.15 – 09.30 Löwner R., Conze R., Wächter J., Krysiak F., Laframboise R., and the Mallik working group: Mallik 2002: The Mallik Data and Information System 09.30 – 09.45 Schultz H.J., Deerberg G., Schlüter S., Fahlenkamp H.: Simulation of the oceanic gas hydrate removal using the mammoth-pump-principle (550 A) QUANTIFICATION AND CHARACTERISTICS OF GAS HYDRATES (H. VILLINGER, W.F. KUHS) 09.45 – 10.00 Kuhs W.F., Klapproth A., Itoh H., Goreshnik E.: Physico-chemistry and properties of gas hydrates : Preliminary answers to some open questions 10.00 – 10.15 Klaucke I., Weinrebe W., Bohrmann G.: Geoacoustic mapping of near-surface gashydrates and associated features in the Black Sea using deep-towed, high-resolution sidescan sonar (OMEGA) 10.15 – 10.30 Brückmann W., Linke P., Mörz T., Türk M., Poser M.: In-Situ Characterization of Gas Hydrates (OMEGA) 10.30 – 10.45 Steffen H., Gust G.: Experimental and theoretical concepts to quantify deep-sea environments in an Autoclaved Experimental Chamber (AEC) (OMEGA) 10.45 – 11.15 Coffee break

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11.15 – 11.30 Erzinger J. (co-ordinator), Spangenberg E., Schicks J., Naumann R., Lüders V., Möller P., Kukowski N.: Experimental determination of physical and physico-chemical properties of gas hydrate-bearing sediments (Project 555A- Overview) 11.30 – 11.45 Schicks J., Lüders V., Möller P.: Raman Spectroscopic measurements of gas hydrates (555 A) 11.45 – 12.00 Baumert J., Gutt C., Press W., Tse J., Janssen S.: Dynamics of Gas Hydrates (551 A) 12.00 – 12.15 Müller C., Bönnemann C., Neben S.: Detailed Seismic Study of a Gas Hydrate Deposit Offshore Costa Rica (DEGAS) 12.15 – 12.30 Lüdmann T., Wong H.K., Konerding P.: A first estimate of the volume of methane gas associated with gas hydrate occurrence in the Dnieper Canyon area, northwestern Black Sea (GHOSTDABS) 12.30 – 12.45 Grupe B., Kreiter S., Feeser V., Hoffmann K., Becker H.J., Savidis S., Schupp J.: Slope Stability and Land Slides in the Deep Sea: Influence Parameter Gas Hydrates (GASSTAB) 12.45 – 13.00 Zühlsdorff L., Spieß V., Schwenk T., Chapman N.R., Riedel M., Hyndman R.D.: MultiFrequency Seismic Data in the Vicinity of a Gas Hydrate Site at the Northern Cascadia Accretionary Prism (LOTUS) 13.00 – 14.00 Lunch break 14.00 – 15.00 Closing session & final discussion ca. 15.00 End of the meeting

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POSTER PRESENTATION GLOBAL CARBON CIRCLE AND CLIMATE EFFECTS 1. Krüger M., Treude T., Nauhaus K., Eppelin A., Boetius A., Widdel F.: Microbial methane turnover in different types of marine sediments – The MUMM-Project 2. Treude T., Boetius A., Knittel K., Rickert D.: Anaerobic oxidation of methane above gas (MUMM) 3. Nauhaus K., Treude T., Gieseke A., Knittel K., Boetius A., Michaelis W., Widdel F.: Massive Structures in the anoxic Black Sea: Biomass and carbonate formation based on the anaerobic oxidation of methane (MUMM) 4. Knittel K., Boetius A., Lemke A., Amann R.: Molecular Ecology of Anaerobic Oxidation of Methane (BMBF/Geotechnologien project ”MUMM”) 5. Lösekann T., Nadalig T., Knittel K., Boetius A., Sauter E., Schlüter M., Klages M., Amann R.: Distribution of Methanotrophic Microbial Communities at the Haakon Mosby Mud Volcano (MUMM project) 6. Niemann H., Elvert M., Boetius A.: Biomarker evidence of methane oxidation in sediments of Haakon Mosby Mud Volcano (MUMM) 7. Seifert R., Blumenberg M., Pape T., Peterknecht K., Thiel V., Schmale O., Sültenfuß J., Rhein M., Michaelis W.: Gases and dissolved carbon compounds in the north-western Black Sea – concentrations and isotopic compositions (I + II) (GHOSTDABS) 8. Fischer H., Richter K.-U.: The role of gas hydrates in the course of rapid climate changes - Isotopic studies on methane in polar ice cores (549 A) 9. Mangelsdorf K., Dieckmann V., Wilkes H., Horsfield B., and the Mallik working group: Deep microbial ecosystem: biogeochemical characterisation and its potential substrate feedstock (Mallik Research Well 5L-38) 10. Luff R., Wallmann K.: Biogeochemical turn over in methane rich sediments at Hydrate Ridge, Cascadia Margin: Quantification using a model approach (LOTUS) 11. Drews M., Schmaljohann R., Aloisi G., Wallmann K.: Microbiological and geochemical investigations at gas hydrate sites in the Black Sea (OMEGA)

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TECHNOLOGICALl AND METHOLOGICAL DEVELOPMENTS 12. Drews M., Holscher B., Gust G., Wallmann K.: Gas hydrate formation and dissolution experiments in a pressure chamber (OMEGA) 13. Sommer, S., Pfannkuche, O., Linke, P., Gust, G., Gubsch S.: A novel benthic chamber for long-term in situ observation and experiments (LOTUS) 14. Löwner R., Conze R., Wächter J., Krysiak F., Laframboise R. and the Mallik working group: Mallik 2002: The Mallik Data and Information System 15. Schultz H.J., Deerberg G., Schlüter S., Fahlenkamp H.: Program for the simulation of gas hydrate equilibrium (550 A) 16. Schmidt-Brauns J., de Beer D.: Development of a Methane Biomicrosensor for Deep Sea Applications (MUMM) 17. Mörz T., Brückmann W., Linke P., Türk M., Poser M.: HDSD – Hydrate Detection and Stability Determination - A Tool For In-Situ Gas Hydrate Destabilisation (SFB 574) 18. Theilen Fr., Klein G., Thießen O., Schmidt M., Bohlen T.: NATLAB: Seismic Parameters and Physical Properties of Marine Sediments (INGGAS) 19. Gennerich H.-H., Grevemeyer I., Kaul N., Villinger H.: INGGAS-Flux: New tools for energy and fluid-flux: pore pressure and thermal gradient probes 20. Kulenkampff J., Spangenberg E., Naumann R.: Experimental methods for the laboratory investigation of gas hydrate containing sediments (555 A) 21. Greinert J., Keir R., Spieß V.: Quantification of dissolved and free methane at gas hydrate associated cold vents: The use of lander and ship mounted hydro acoustic systems and methane sensors QUANTIFICATION AND CHARACTERISTICS OF GAS HYDRATES 22. Spangenberg E., Kulenkampff J.: Physical Properties of Hydrate Bearing Sediments (555 A) 23. Henninges, J., Schrötter J., Erbas K., Huenges E., and the Mallik working group: Temperature profiles during a gas hydrate production test (MALLIK) 24. Bönnemann C., Behain D., Meyer H., Neben S., Müller C.: Recent seismic investigations on gas hydrates at convergent margins by BGR 25. Spieß V., Zühlsdorff L., von Lom-Keil H., Schwenk T.: Imaging of the internal structure of fluid upflow zones with detailed digital Parasound echosounder surveys (LOTUS) 26. Bünz S., Mienert J., Andreassen K.: Gas hydrate reservoir characterization using multicomponent wide-angle and ocean bottom cable seismic data

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27. Itoh H., Goreshnik E., Klapproth A., Kuhs W.F.: Structure and dynamics of gas hydrates: Recent results 28. Staykova D.K., Goreshnik E., Salamatin A.N., Kuhs W.F.: Formation Kinetics of Porous Gas Hydrates 29. Bohrmann G., Suess E., Kuhs W.F., Rickert D., Gunkel T., Techmer K., Heinrich T., Abegg F., Linke P., Wallmann K.: Properties of Sea Floor Methane Hydrates at Hydrate Ridge, Cascadia Margin (OMEGA) 30. Abegg F., Freitag J., Bohrmann G., Kipfstuhl S., Brückmann W.: Structures of Gas Hydrates (OMEGA) 31. Krastel S., Spieß V., Zühlsdorff L.: MARGASCH – Marine gas hydrates of the Black Sea: First results from a high resolution 3D multichannel seismic survey (LOTUS) 32. Lom-Keil H. von, Spieß V., Krastel S., Greinert J., Artemov Y.: Acoustical studies in the water column in vicinity of Cold Vents and Mudvolcanoes (LOTUS)

ASSOCIATED THEMES 33. Hübner A., Halbach P.: Pyrite Crusts from the Black Sea: Mineralogy and Genesis (GHOSTDABS) 34. Reimer A., Peckmann J., Reitner J.: Methane-derived carbonate mineralisation in the northwestern Black Sea (GHOSTDABS)

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Structures of Gas Hydrates Abegg F. (1), Freitag J. (2), Bohrmann G. (1), Kipfstuhl S. (2), Brückmann W. (1) (1) GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, 24148 Kiel, Germany (2) Alfred Wegener Institute for Polar and Marine Research, Columbusstraße, 27568 Bremerhaven, Germany

Geophysical methods provide information on gas hydrate distribution on a scale ranging from tenths of meters up to kilometers. Based on cores from discrete locations the distribution and properties of the hydrates can be investigated on a scale from meters down to microns. Within OMEGA subproject 2 we use X-ray computed tomographic (CT) imaging to look at the small scale interaction of gas bubbles, hydrates and sediment to be able to contribute to questions of quantification, structure and physical properties.

We have applied two different types of CT scanner. One scanner, normally used for medical purposes, is used to investigate samples of tenths of a centimeter in one dimension and up to 1.6 m in the other dimension. Up to now the samples are all preserved in liquid nitrogen and are also scanned in deep frozen condition.

The other scanner is a micro CT scanner for non-destructive three-dimensional microscopy.

The sample volume is limited to a size of 30x20.5 mm3. The scanner is located in the AWI-Bremerhaven in a cold laboratory with a permanent temperature of –25°C. Samples from two different regions have been scanned. From R/V SONNE cruise 148 (project TECFLUX, July/August 2000) to the Hydrate Ridge off the Oregon Coast a large set of 23 gas hydrate samples, taken with a TV-guided grab sampler, is used. The second set of samples has been taken during METEOR cruise 52 to the Black Sea (project OMEGA and INGGAS). The samples have been taken with gravity corer and TV-guided grab sampler.

In general the gas hydrates used in this study can be grouped into three classes with certain transitions. Without establishing a hierarchy, the first class consists of hydrates with large

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bubble-like voids. Fig. 1 shows a wide space in the sediment filled with an array of bubbles.

The arch of the bubble skin, built from gas hydrate, indicates the orientation during formation.

The second group consists of dense nonhomogeneous gas hydrate which has no bubble-like spaces and the third group to be mentioned are gas hydrate layers alternating with sediment layers. These groups have been chosen for the sake of description but there are

Figure 1: CT slice indicating gas in white, gas hydrate in light gray, sediment in dark gray and black.

also examples where transitions could be seen between groups in one sample. Subsequent data processing of the scan data provides information about the percentages of gas, gas hydrate and sediment within the sample.

Besides samples with gas hydrate close to 100%, the gas content may reach values of about 10%.

Autoclave sampling and in-situ preservation system, status and outlook, March 2002 Amann H., Hohnberg H.-J. Technische Universität Berlin, FG Maritime Technik (MAT), Müller-Breslau-Straße VWS, 10623 Berlin, Germany

Gashydrate research in the ocean needs autoclave sampling and monitoring probes for groundtruthing ephemeral gashydrates by pristine cores. In-situ conditions, first of all pres-sure but also temperature, sediment mechanical properties and geochemistry, must be preserved in order to understand structure, formation, eventual uses and environmental conditions of marine gashydrates. Fachgebiet Maritime Technik of Technische Universität Berlin, a partner in OMEGA, is developing such tools, which, in addition, are being safety certified by TÜV as pressure vessels. The MultiAutoclave-Corer MAC takes four 50 cm long cores, diameter 100 mm, from the seafloor surface, by slow penetration and thus preserving the sediment structure. A 4 liter headspace for sea-floor- and downhole water constitutes a reservoir for in-situ chemical conditions. Figure 1 shows the engineering concept before the last redesign in 2000. The ultimate hardware system will be presented on the Status Symposium on May 6 in Kiel. DAPC is a dynamic autoclave piston corer for 2 m core recovery, (Fig.2). Autoclave cores taken from both tools will be pressure stored onboard and there will be scientific access opportunities for MAC cores, eg for pressurized subsampling.

The main scientific investigation method of the in-situ core in the autoclave should be computer tomography, CT, to xray the phase contents and possibly the in-situ sediment structure.

element, for CT analyses; a zero degree seawater container, shielding the autoclave section for temperature control; an access port at the upper side for pressurized subsampling; avoidance of flanges for weight reduction and smooth penetration; external seawater flow through the annulus to the cutting shoe to facilitate coring; optionally and adapted from a different development project: a system for measurement while sampling (salinity, temperature, pressure, dissolved oxygen, pH, particle content).

MAC will be offshore tested on May 6 and 7, 2002, with RV Alkor in the Baltic. Upon commissioning during the same test cruise, it shall be transported lateron to RV Sonne for the research cruise OTEGA on the Oregon Hydrate Ridge in July and August. Some subsystems of the DAPC, the autoclave piston corer, are available already. Upon a design review the system is being redesigned during the forthcoming months. It shall be detail designed, manufactured and offshore tested until the first quarter of 2003. MAC and DAPC should be ready for standard use, as scheduled, for gashydrate research and exploration projects in 2003.

MAC and DAPC integrate a number of novel technical elements: a failsafe hingeless flapvalve to warrant the autoclave function in downhole conditions; a GRP pipe as transparent pressure vessel (200 bar), complemented by an aluminium pipe segment as axial-tension

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Figure 1: MAC, Multi-AutoclaveCorer, side view. Designed by MAT (Maritime Technik) TU BERLIN.

Figure 2: DAPC, Dynamic Autoclave Piston Corer.

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Crosshole seismic monitoring before and during a gas hydrate stimulation test (Mallik research wells 3L-38, 4L-38 and 5L-38) Bauer K. (1), Pratt R.G. (2), Weber M.H. (1), Harris J.M. (3), Shimizu S. (4), and the Mallik working group (1) GeoForschungsZentrum Potsdam (2) Queen’s University at Kingston (3) Stanford University (4) Japan National Oil Corporation

To date, surface seismic data in combination with drilling results represent the most important source of information for mapping gas hydrate occurrences in a regional to global scale. However, qualitative and, much more, quantitative interpretation suffers from the relatively little knowledge on petrophysical properties of gas hydrate bearing sediments, and the limitations in resolution compared with the fine-scale strata and possible lens structures as revealed from drilling hydrate reservoirs (e.g., Dallimore et al., 1999). There-

fore, case studies are needed at well known sites where direct borehole and petrophysical core analysis can be combined with seismic measurements for a wide range of scale lengths, to allow for scaling, from downhole to surface seismic experiments. In that context, crosshole observations establish a missing link between downhole logging on the one hand, and surface-borehole and surface measurements on the other hand (Figure 1), that was, to our knowledge, not covered in gas hydrate research so far.

Figure 1

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The Mackenzie Delta belongs to the best studied regions where gas hydrate accumulations formed under permafrost conditions (e.g., Dallimore et al., 1999, Majorowicz and Osadetz, 2001). The JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well provided a wide variety of geological, geophysical and geochemical information on the gas hydrate bearing sediments at this location (Dallimore et al., 1999). Seismic properties including P and S velocities, and attenuation were deduced from downhole ultra-sonic and vertical seismic profile (VSP) measurements (Collett et al., 1999, Guerin and Goldberg, 2001, Sakai, 1999, Walia et al., 1999). Based on these results, several seismic experiments were proposed as part of the Mallik 3L-38, 4L-38 and 5L-38 research wells to allow for a systematic seismic scaling study. The program included downhole ultra-sonic logging (Project leader (PL) United States Geological Survey (USGS), Japan National Oil Corporation (JNOC) and Japan Petroleum Exploration Company (JAPEX)), crosshole measurements (PL GeoForschungsZentrum (GFZ) Potsdam, together with Queen's University at Kingston, Stanford University, JNOC, JAPEX, and University of Kyoto), a VSP survey (PL University of Toronto), and a 3-D surface seismic experiment (PL University of Alberta, Edmonton). Extensive geological and petrophysical core analysis will provide an excellent base to substantiate interpretation of the resulting seismic images and parameter estimations.

In addition to seismic characterization at different scale lengths, the main objective of the seismic experiments was to investigate the suitability of different seismic methods to monitor changes of seismic properties related with thermal stimulation tests to produce methane gas from hydrates.

The crosshole seismic measurements were carried out by making use of two 1150 m deep observation wells (Mallik 3L-38 and 4L-38) both 40 m from and co-planar with the 1170 m deep production test well (5L-38). The program included one baseline survey before and

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3 repeat surveys after the beginning of a thermal stimulation test. A high power piezo-ceramic source was used to generate sweeped signals with frequencies between 100 and 2000 Hz that were recorded with arrays of 8 hydrophones per depth level. During the baseline experiment, the depth interval between 800 1150 m was covered. A dense source and receiver depth spacing was choosen as 0.75 m to increase spatial resolution. Angular coverage was between +– 50 degrees against the horizontal axis. Based on tests, a stack of two sweeps per depth level during the initial experiment was adequate for acceptable signal-tonoise ratios. Acquisition parameters were slightly adapted during the 3 monitoring experiments and a total depth interval between 800 and 1050 m and one sweep per depth level were used.

First inspection shows that high quality data were collected during the crosswell seismic experiments. Initially, processing and modelling is focussed on the analysis of the baseline survey data to derive high resolution seismic images characterizing the gas hydrate bearing sediments before starting the stimulation tests.

First, very strong tube wave energy generated in both observation wells had to be suppressed by multi-trace filtering in the source and receiver gather domain. The following data analysis is aimed to generate velocity models based on standard travel time tomography and, to achieve higher resolution, full waveform inversion techniques (Pratt, 1999). Further processing will include attenuation tomography, reflection imaging and connectivity mapping using guided waves. The resulting reference models will be interpreted together with results from other geophysical experiments and petrophysical core analysis and modeling.

References Collett, T. S., Lewis, R. E., Lee, M. W., Uchida, T., Detailed evaluation of gas hydrate reservoir properties using JAPEX/JNOC/GSC Mallik 2L38 gas hydrate research well downhole welllog displays, In: Scientific results from JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, Northwest Territories, Canada, (ed.) Dallimore, S.R., Uchida, T., and Collett, T.S., Geological Survey of Canada, Bulletin 544, 295-311, 1999.

Walia, R., Mi, Y., Hyndman, R.D., and Sakai, A., Vertical seismic profile (VSP) in the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well. In: Scientific results from JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, Northwest Territories, Canada, (ed.) Dallimore, S.R., Uchida, T., and Collett, T.S.; Geological Survey of Canada, Bulletin 544, 341-355, 1999.

Dallimore, S. R., Collett, T. S., and Uchida, T., Summary - Sommaire. In: Scientific results from JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, Northwest Territories, Canada, (ed.) Dallimore, S.R., Uchida, T., and Collett, T.S., Geological Survey of Canada, Bulletin 544, 1-10, 1999.

Guerin, G, and Goldberg, D., Sonic waveform attenuation in Gas Hydrate-bearing sediments from the JAPEX/JNOC/GSC Mallik 2L-38 research well, Mackenzie Delta, Canada, submitted to J. Geophys. Res., 2001.

Majorowicz, J. A., and Osadetz, K. G., Gas hydrate distribution and volume in Canada, AAPG Bull. 85, 7, 1211-1230, 2001.

Pratt, R. G., Seismic waveform inversion in the frequency domain, Part 1: Theory and verification in a physical scale model, Geophysics, 64, 3, 888-901, 1999.

Sakai, A., Velocity analysis of vertical seismic profile (VSP) survey at JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, and related problems for estimating gas hydrate concentration. In: Scientific results from JAPEX/JNOC /GSC Mallik 2L-38 gas hydrate research well, Northwest Territories, Canada, (ed.) Dallimore, S.R., Uchida, T., and Collett, T.S.; Geological Survey of Canada, Bulletin 544, 323-340, 1999.

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Dynamics of Gas Hydrates Baumert J. (1, 3), Gutt C. (2), Press W. (3), Tse J. (4), Janssen S. (5) (1) IEAP, Universität Kiel, Germany (2) Experimentelle Physik I, Universität Dortmund, Germany (3) ILL, Grenoble, France (4) NRC, Ottawa, Canada (5) PSI, Villigen, Switzerland

Gas hydrates are a special class of inclusion compounds, in which small hydrophobic guest molecules or atoms are trapped in cages formed by an ice-like host lattice of water molecules. In recent years the clathrate hydrates have attracted considerable interest as large deposits of methane hydrate have been found on the oceanic sea floors. The methane gas stored in the hydrate deposits may serve as future energy supply whereas instabilities may have implications for the global climate through the release of large amounts of methane. Therefore, the understanding of the physical properties of methane hydrate is of great interest.

As gas hydrates consist to 80% of hydrogen bonded water molecules the physical properties are expected to be similar to those of ice Ih. This, however, is not true for the thermal conductivity, which is a factor 5 smaller at T<0ºC (0.5 W/Km) than in ice Ih and even more surprisingly displays a temperature dependence similar to that of glasses despite the crystalline character of the clathrate hydrates [1]. This behaviour may play an important role for the modelling and prediction of stability of continental hydrates and hydrates in shallow arctic water.

In the case of the gas hydrates the guest-host interaction is weaker than the bond strength of the cage structure. Nevertheless it is this hydrophobic interaction, which stabilises the ice framework and is thought to be responsible for a coupling between the localised low frequency vibrations of guest molecules and the vibrations of the host lattice. The rattling modes of the encaged guest molecules can therefore act as effective scattering centres for

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the heat carrying phonons, reducing the thermal conductivity and leading to the glass-like temperature dependence.

We were able to confirm this coupling in a high-resolution inelastic incoherent neutron scattering experiment (IINS) on xenon hydrate by finding three distinct low frequency excitations at 2.05 meV, 2.87 meV, and 3.94 meV [2,3] (Fig. 1). Xe-hydrate has as methane hydrate the cubic structure I consisting of 6 large and 2 small cages in the unit cell. As the total incoherent scattering cross section of the water molecules exceeds the cross section of the xenon guest atoms by a factor 1000, the IINS signal arises from the H-atoms, thus only displaying the density of states (DOS) of the host lattice vibrations. Lattice dynamical calculations show that the coupling can be described as a symmetry avoided crossing, which leads to a strong optic behaviour of the acoustic host lattice modes in the frequency region of the localised xenon modes. As the Xe-atoms in the small spherical cage vibrate with the highest frequency and in the larger ellipsoidal cage with two lower frequencies, this gives raise to the three observed peaks.

We also report of IINS experiments on methane hydrate focussing on its low frequency vibrations. The experiments were performed with partially deuterated samples. Due to the deuteration of the host lattice only the modes of the encaged methane molecules are visible in the spectra. A broad quasielastic background from the rotational excitations of the methane molecules was observed. Furthermore broad inelastic excitations were visible in an energy region from 4 meV to 15 meV with a distinct peak at 5.3 meV, which can be attri-

buted to vibrations of the methane molecules inside the cages. The broad excitations from 7 meV to 13 meV probably also reflect the density of states of the host lattice. This points again towards a coupling between the guest and host vibrations.

The temperature dependence of the guest modes shows that the repulsive part of the guest-host interaction, which stabilises the ice framework, plays an important role in the coupling mechanism. In both xenon and methane hydrate the guest modes were found to shift towards higher frequencies with increasing temperature. Therefore anharmonic terms should play a considerable role in the guest-host interaction.

Another important physical property is the velocity of sound of methane hydrate. Due to the importance of the hydrate deposits, reliable means of hydrate detection as well as good modelling of hydrates in sediments are necessary. The modelling of the hydrates in sediments requires the knowledge of both the elastic constants and the sound velocity, which is also necessary as calibration for the seismic detection techniques. So far no microscopic measurements on natural or synthesised samples have been reported and access to these quantities by macroscopic means is difficult. In Brillouin light scattering experiments the refraction index and cage occupancy has to be calculated or assumed. Additionally methane hydrate samples don't display the optimal optical quality needed for well-defined measurements of the velocity of sound [4].

Very recently we could determine the longitudinal velocity of sound of methane hydrate directly from the dispersion of the longitudinal acoustic host lattice mode in an inelastic x-ray scattering experiment (Fig. 2). Both the optic guest mode, arising from the localised vibrations of the methane molecules inside the cages, and the longitudinal acoustic (LA) host lattice mode are observable. The LA mode displays about the same energy dispersion as a function of the wavevectortransfer k as the LA mode in ice. From the dispersion an orientationally averaged longitudinal velocity of sound of about 3900 m/s was derived [5], which is

somewhat higher than the values found in Brillouin light scattering experiments.

The region where the two modes intersect is additionally of special interest as it contains information about the mixing of the modes and thus the coupling of the guest and host vibrations. The linewidth of the LA host lattice mode furthermore yields information about the phonon lifetime in methane hydrate, which can be related to the thermal conductivity.

Figure 1: IINS spectrum of Xe-hydrate (Xe 5.75 H2O) at T=100K. The three distinct low energy peaks at 2.05 meV, 2.87 meV and 3.94 meV are due to the coupling of guest and host vibrations (FOCUS-spectrometer PSI).

Figure 2: The dispersion curve for methane hydrate at T=100K. The mode at 5 meV displays a strong optic behavior corresponding to the localized vibrations of the methane molecules inside the water cages. In a first step, the velocity of sound was derived from the linear dispersion of the LA lattice mode.

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References: [1] R.G. Ross, P. Anderson, G. Backstrom, Nature 290, 322 (1981) [2] J.S. Tse, V.P. Shpakov, V.R. Belosludov, F. Trouw, Y.P. Handa, W. Press, Europhys. Lett.

54, 354 (2001) [3] C. Gutt, J. Baumert, W. Press, J.S. Tse, S. Janssen, J. Chem. Phys. 116, 3795 (2002) [4] H. Kiefte, M.J. Clouter, R.E .Gagnon, J. Phys. Chem., 89 3103 (1985) [5] J. Baumert, C. Gutt, H. Requardt, M. Krisch, W. Press, M. M端ller, J.S. Tse to be published

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Recent seismic investigations on gas hydrates at convergent margins by BGR Bönnemann C. (1), Behain D. (2), Meyer H. (1), Neben S. (1), Müller C. (1) (1) Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover (2) Technische Universität Clausthal, Institut für Geophysik, Arnold-Sommerfeld-Straße 1, 38678 Clausthal-Zellerfeld

In the last years all marine seismic cruises of BGR on convergent margins revealed deposits of gas hydrates. The standard analysis of these data begins with the mapping of the BSR (bottom simulating reflector) in the processed reflection seismic data to achieve an estimate of the minimal extension of the gas hydrates.

The BSR is not in all cases clearly visible, it can be masked by diffractions (in stacked data) or by reflections from complex structures. Also high-reflective sedimentary sequences, parallel to the slope of the seafloor, can aggravate the identification of the BSR. Finally, in the case of gas hydrate without free gas trapped below the BSR can be very week or absent.

The second standard analysis tool is the derivation of the heat flow from the depth parameters of the BSR at selected locations. This gives valuable data for further analysis and interpretation.

The work of BGR with these data has a variety of objectives: reservoir investigations, structural studies, comparative studies to understand the origin of the gas and to assess the role of gas hydrates and the free gas beneath it as a possibly future energy source. The following areas will be shortly discussed: Active margin of Costa Rica (SO81, BGR cruises) The convergent continental margin of Costa Rica is an area with large known gas hydrate occurrences. At this margin BGR undertook in 1992 a 3D seismic survey and acquired 2D seismic data during several cruises. The mapping of the BSR (Fig. 1) from these data reveals five

different areas of gas hydrates and indications for a strong variability of the heat flow. The distribution is controlled by tectonism, slopes and the roughness of the subducting crust.

The 3D seismic data and high-resolution 2D data from cruise BGR99 are subject of a detailed seismic study of a gas hydrate reservoir study (DEGAS project in the framework of the Geotechnologien program).

Sunda Arc (SO137 GINCO cruise) The Sunda subduction zone formed the Mentawai and the Java forearc basins. Gas hydrates are observed mostly in boundary parts of the basins and in the anticlinal structures in depths between 1300 mbsl and 3800 mbsl (Fig. 2). In the center of the basins the BSR is either weak, obscured or totally absent.

The derived heat flow in the basis ranges between 35 and 44 mW/m2. The values at the boundaries are much higher which could be explained by fluid circulation.

Active margin of middle Chile (SO161 SPOC) Gas hydrate has been observed only in the southern part of the working area of the SPOC cruise. They occur mainly on the middle slope and are formed in lenghty patches parallel to the coast.

Continental margin off Sabah (South China Sea) The nature of this margin is still under discussion. Some authors believe that it is since post early Middle Miocene an inactive continental margin. Gas hydrates occurrences were found

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in depths between 1300 mbsl and 2800 mbsl.

They occur mainly on the hanging walls and the top of the anticlines in the Baram Delta Thrust Toe, the compressed thrust toe and the lower tertiary thrust sheets. Isotope analyses and thermal maturity modeling suggest a mixture of bacterial and thermal generation for the gases inside the gas hydrates off NW Sabah.

Figure 1: Stacked seismic section of line BGR99-54 at the active margin of Costa Rica at seaward extension of BGR92 3D box across the Middle America Trench (MAT). A stromg BSR is recognizable approximately 0.2-0.55 TWT bsf. The geothermal gradients were estimated from BSR depths.

Figure 2: Distribution of gas hydrates at the Sunda arc, marked in light blue.

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The enigmatic process of anaerobic oxidation of methane: first results of project MUMM Boetius A. (1, 2, 3), Amann R. (1), de Beer D. (1), Elvert M. (1), Jørgensen B.B. (1), Knittel K. (1), Krüger M. (1), Lemke A. (1), Lösekann T. (1), Nauhaus K. (1), Niemann H. (1), Schmidt J. (1), Treude T. (1), Witte U. (1), Widdel F. (1) (1) Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany (2) Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27515 Bremerhaven, Germany, fon 49-471-4831-1518, fax 49-471-4831-1425, email: aboetius@awi-bremerhaven.de (3) International University Bremen, 28725 Bremen, Germany

Stable isotope signatures, radiotracer and modeling techniques have established that most of the methane in marine sediments is oxidized microbially under anoxic conditions.

This has been observed in the methane-sulfate transition zone of subsurface sediments as well as in surficial sediments of cold seeps, mud volcanoes and above dissociating gas hydrates.

As the major biological sink of methane in marine sediments, the microbially mediated anaerobic oxidation of methane (AOM) is crucial in its role of maintaining a sensitive balance of our atmosphere’s greenhouse gas content. However, details of the related biochemical mechanisms and organisms are still largely unknown. Understanding the geological, biological and biochemical details of AOM is the goal of our research group, in a combined effort of biogeochemists, molecular ecologists and microbiologists using novel analytical tools tailored for the study of unknown microbes and habitats. The discovery of Archea-SRB aggregates involved in the anaerobic oxidation of methane in gas hydrate sediments (GEOMAR programmes TECFLUX I+II) has been a major progress in the study of this process and has shown the direction of future research.

Under the umbrella of the project "MUMM" and in collaboration with colleagues within the MPI, the Alfred Wegener Institute for Polar and Marine Research, the GEOMAR, the University Bremen, the University of Hamburg, the University of Georgia, the IFREMER and various others European and International partners, the biogeochemistry, molecular ecology and

microbiology of the process of anaerobic oxidation of methane and the microbial consortia involved are studied in different sediment systems. These include gas hydrates, cold seeps, mud vulcanoes as well as the omnipresent sulfate-methane interface of shelf sediments. The goal is to understand the pathway of methane oxidation through the consortium and how the physiology and ecology of the involved microorganisms regulate the process.

Experimental studies will be done on sediments and enrichments to trace the fate of methane carbon and analyze the environmental factors which determine the process rate.

During the first year of MUMM, we participated in 5 expeditions including investigations of methane seeps in the Black Sea, gas hydrates and petroleum seeps in the Gulf of Mexico, an North-Atlantic mud volcanoe. We will further explore methane production and breakdown in the seabed, and how efficiently the microbial sub-surface methane barrier controls the emission of this important greenhouse gas.

Major new findings were achieved by all groups involved in the project, some of which are summarized below: Presence of consortia of archaea and sulfate reducing bacteria in gassy sediments (also see Knittel et al., this volume) The isotopic and genetic signature of the microbial biomass in methane-saturated seep sediments shows that AOM is mediated by different microbial consortia which generally

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include archaea and sulfate-reducing bacteria.

Fluorescence in situ hybridization revealed that in all gassy sediments investigated, both archaea and bacteria grow together in symbiotic association (Fig. 1). Among the archaea from these sediments, rRNA probes target specifically two different phylogenetic groups of archaea capable of mediating AOM: the ANME-2 group, belonging to the Methanosarcinales, and the ANME-1 group, a new group of archaea only distantly related to the Methanosarcinales.

Figure 1.

Consortia of archaea and sulfate reducing bacteria detected at MUMM study sites (K Knittel, A Boetius).

First in vitro demonstration of the process of AOM (also see Krüger et al., Treude et al. and Nauhaus et al., this volume).

Sediment samples incubated under strictly anoxic conditions in defined mineral medium produced sulphide from sulfate if methane was added as the sole organic substrate. No sulphide production occurred without methane.

An increase of methane pressure resulted in an increase of the sulfate reduction rate with simultaneous production of sulphide at a molar ratio of nearly 1:1. The process itself proved to be psychrophilic. The rates of methane oxidation and sulfate reduction measured in short-term experiments immediately after the retrieval of sediment samples on board of the ships are generally reproducible in the longterm lab experiments. This project is carried

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out in cooperation with the GEOMAR programmes LOTUS and OMEGA).

Discovery of carbonate landscapes in the Black Sea formed by massive microbial mats (see also Nauhaus et al., this volume).

During submersible dives to methane seeps in the permanently anoxic Black Sea, giant microbial structures were discovered, composed of massive microbial mats of centimeter to decimeter thickness, producing large carbonate columns and platforms. Both the microbial biomass and the carbonates are partially derived from methane as indicated by their depletion in 13C. The massive mats are mainly composed of a consortium of archaea and sulfate reducing bacteria, which is responsible for high rates of methane oxidation via sulfate reduction, and for methane incorporation into microbial biomass and carbonates. This project is carried out in cooperation with the University of Hamburg (progamme GHOSTDABS).

Methanotrophic consortia forming an efficient barrier against methane emission to the hydrosphere (see also Lösekann et al. and Niemann et al., this volume).

The Haakon Mosby Mud Volcano (HMMV) is situated on the continental slope northwest of Norway at a water depth of 1250 m. Extensive mats of giant, sufide-oxidizing bacteria were detected, indicative of a rapid production of sulfide from methane via AOM. Beneath these mats, a high biomass of consortia containing ANME-2 archaea was found, obviously capable of oxidizing methane with sulfate at temperatures close to the freezing point (-1°C). The concentration of methane in the bottom waters was extremely high in the center and at the outer rim, but showed a significant drop above the Beggiatoa mats, indicating that the methanotrophic consortia effeciently remove methane rising from the sediments to the hydrosphere. This project is carried out in cooperation with the Alfred Wegener Institute for Polar and Marine Research and with the French research institute IFREMER.

Mud volcanoes and gas hydrates in the Black Sea – an important linkage to the methane cycle (initial results from METEOR cruise MARGASCH M52/1) Bohrmann G. (1), Abegg F. (1), Aloisi G. (1), Artemov Y. (5), Bialas J. (1), Broser A. (1), Drews M. (1), Fouchet J.-P. (6), Greinert J. (1), Heidersdorf F. (2), Ivanov M. (4), Blinova V. (4), Klaucke I. (1), Krastel S. (2), Leder T. (2), Polikarpov I. (5), Saburova M. (5), Schellig F. (3), Schmale O. (3), Spieß V. (2), Volkonskaya A. (4), Weinrebe W. (1), Zillmer M. (1) (1) GEOMAR, Forschungszentrum Kiel, Germany (2) Fachbereich Geowissenschaften der Uni Bremen, Germany (3) Institut für Biogeochemie und Meereschemie, Universität Hamburg, Germany (4) UNESCO-Center for Marine Geosciences MSU, Moskow, Russia (5) A.O. Kovalevsky Institute of Biology of the Southern Seas, Sevastopol, Ukraine (6) FREMER, Plouzané, France

METEOR cruise M52/1 (January 2 to February 1, 2002; Istanbul – Sevastopol- Istanbul) carried out research on gas hydrates in the Black Sea. The leg focused on the distribution, composition, and the structure of gas hydrate occurrences, and their relationship to fluid migration through the sediments and to gas venting. The environmental conditions for the formation of gas hydrates in the Sorokin Trough and to less extent to the central Black Sea have also been the of interest. In both areas gas hydrates have been reported from Russian scientists to occur close to the seafloor. Such hydrates are highly reactive methane reservoirs with extremely variable methane fluxes. The approach used during this leg was highly interdisciplinary and included high-resolution geoacoustical investigations of the seafloor and subbottom using a wide range of frequencies and techniques, video mapping of the seafloor, investigations of the water column, and sampling of sediments and gas hydrates.

Mud volcanoes occur in the central Black Sea and Sorokin Trough (Fig. 1) in a great variety of sizes (up to 2,5 km in diameter). The volcanos may rise as much as 200 m above the seafloor.

In the Sorokin Trough the roots of such mud vol-

canoes are connected to deeper diapiric structures that evolved in the compressional tectonic regime between the Tetyaev and Shatskiy Rises in the south and the Cremean Peninsula in the north. The diapiric folds are formed mostly by clay deposits of the Maikopian Formation (Oligocene-Lower Miocene) which enables fluids and gases to migrate upwards to the seafloor.

The methane gas either forms gas hydrate or emanates to the water column producing acoustic plumes. Near-surface gas hydrates were sampled during the cruise from several mud volcanoes known as Yalta, Dvurechenskii, Odessa and an unnamed mud volcano (Fig. 2). The Dvurechenskii mud volcano in particular is a seepage area with high fluxes. While the normal water temperatures were about 9° C at the seafloor, the upper 6 m sediment in the central part of Dvurechenskii mud volcano showed temperatures of up to 16° C in. An higher temperature anomaly was measured in the bottom water with the CTD mounted on the TV-sled. These high temperatures suggest that the mud is currently rising. In spite of the high temperature, the pressure is high enough in 2000 m water depth to allow the formation of gas hydrates. Alle six sedimentary cores from Dvurechenskii mud volcano contained large amounts of finely

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dispersed gas hydrate that dissociated quickly on board the research vessel. The pore water profiles indicated a strong fluid and/or gas flux from the sediment to the water column. The CTD and water sampling stations at Dvurechenskii mud volcano were the only sites where higher methane concentrations were measured in the bottom water, indicating a strong methane flux from an active mud volcano.

Seismic overview profiles over a large number of mud volcanoes were conducted to define a tar-

get area for a 3D-seismic survey, which was then performed at the Sevastopol mud volcano. An area of 7 x 2.5 km was covered by high-resolution reflection seismic work and OBS/OBH refraction seismic studies in order to obtain detailed images of the pathways that gases and fluids take when moving upwards. In addition to providing information about sedimentary layering and tectonic processes, the combined data will help to quantify the spatial characteristics concerning the locations and the quantities of gas hydrate enclosed in the sediment.

Figure 1: Locations of mud volcanos in the Sorokin Trough (Black Sea).

Figure 2: Sites of sampling during MARGASCH cruise M52/1 in the Sorokin Trough (Black Sea).

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Properties of Sea Floor Methane Hydrates at Hydrate Ridge, Cascadia Margin (OMEGA) Bohrmann G. (1), Suess E. (1) , Kuhs W.F. (2), Rickert D. (1), Gunkel T. (1), Techmer K. (2), Heinrich T. (2), Abegg F. (1), Linke P. (1), Wallmann K. (1) (1) GEOMAR Research Center for Marine Geosciences, Kiel, Germany (2) GZG Geological Center, University of Gรถttingen, Germany

Hydrate Ridge, at the Cascadia convergent margin, harbors a variety of methane hydrates in near-surface sediments. On its southern summit clathrates are exposed on the seafloor and are populated by a methane-oxidizing bacterial consortium that provides the driving force for high benthic biological activity and carbonate precipitation. Here hydrates coexist with bubbles of free methane gas, which migrates upwards from beneath the hydrate stability zone. During several research cruises we recovered gas hydrate samples with a large variety of fabrics. The samples show dense interfingering of gas hydrate with soft

sediment. In most cases, pure white hydrate occurs in layers several millimeters to several centimeters thick. Host sediment is often present as small clasts within the pure gas hydrate matrix. On a macroscopic scale, the fabric varies from highly porous (with pores of up to 5 cm in diameter; Fig. 1A) to massive (Fig. 1B).

Figure 1: Typical gas hydrate fabrics from sediments of southern Hydrate Ridge. Highly porous hydrate framework (A) and massively layered, dense gas hydrate (B). Fieldelectron scanning micrograph from a macroscopic porous hydrate (C); FE-REM image from a dense hydrate specimen showing a homogenous distribution of nano-pores in the range of 100-400 nm.

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Wet bulk densities of 80 pure hydrate samples measured onboard RV SONNE range from 0.35 g/cm3 to 7.5 g/cm3 and show a negative correlation between density and percentage of pore space (Fig. 2). Pore space was estimated from the change in volume before and after compression of each sample on a hydraulic press to approximately 160 bar. The samples show high variability in pore volumes ranging from 10-70 vol.% (Fig. 2). Fitting a line to the density versus pore space data, we estimate the end-member density at zero porosity to be approximately 0.81 g/cm3, which is 0.1 g/cm3 less than the theoretical material density of pure methane hydrate (0.91 g/cm3). We attribute the difference in density to sub-micron porosity of the hydrates that cannot be measured with the technique used for the determination of pore volume. The sub-micron porosity (nano-porosity) is documented by a more or less homogenous three-dimensional sponge-like texture observed by field-emission scanning electron microscopy (Fig. 1D). These sub-micron pores have typical sizes of 100-400 nm, and have been observed in both natural and artificial gas hydrates.

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The low bulk density of natural methane hydrates from Hydrate Ridge results in an enormous positive buoyancy force, implying that the hydrate remains on the seafloor only because of the shear strength of the host sediment. We speculate that slabs of hydrate may break off from the seafloor and rise to the sea surface, even when the hydrate is covered with sediment. We believe that the chaotic seafloor topography of small mounds and depressions, observed on southern Hydrate Ridge during ALVIN and ROPOS surveys, is result from this process, which may constitute an important transport mechanism for methane from the seafloor to the atmosphere.

Figure 2: Bulk densities and pore volumes of 15 gas hydrate samples from Hydrate Ridge, measured onboard research vessel SONNE during SO148.

A Deep-Towed Digital Multichannel Seismic Streamer for Very High-Resolution Studies of Marine Subsurface Structures - System Development and First Results of RV Sonne Cruise SO162 (INGGAS Test) Breitzke M., Bialas J., and INGGAS working group GEOMAR Research Centre for Marine Geosciences, Wischhofstrasse 1 - 3, 24148 Kiel, Germany, mbreitzke@geomar.de, jbialas@geomar.de

The vertical and lateral resolution of marine subsurface structures in reflection seismic images strongly depends on the marine seismic source and streamer system used for signal generation and data acquisition. The vertical resolution is controlled by the dominant frequency and bandwidth of the reflected signals and can be improved by using high(er)-frequency sources like GI- or waterguns in deep and boomers or sparkers in shallow water. Deconvolution tries to improve the vertical resolution by increasing the bandwidth. The lateral resolution is determined by the size of the Fresnel zone whose radius depends on the source and streamer depth and on the depth of the reflector, respectively, on the velocity above the reflector and on the dominant frequency. Migration decreases the in-line resolution and radius of the fresnel zone to minimum a quarter wavelength but has no influence on the cross-line resolution. The latter can only be improved by lowering the streamer and - in the ideal case - the source towards to the sea floor. This is the main objective of INGGAS subproject 3.

During 2001, a hybrid multichannel digital deep tow seismic streamer has been developed in order to collect marine seismic data with an improved lateral in- and cross-line resolution particularly in regions of special interest for gas hydrate research. In this context, hybrid system means that conventional marine seismic sources like air-, GI or waterguns shot close to the

surface will still be used, whereas the streamer is lowered to the sea floor and - combined with a side scan sonar system acquired within the OMEGA project of the gas hydrate initiative of the GEOTECHNOLOGIEN program forms a deep-towed device. A depressor of about 2 tons weight completes the deep tow system and ensures the side scan sonar and streamer to keep in depth and as close to the towing ship as possible (Fig. 1).

Figure 1: Deep tow streamer and side scan sonar elements ready for deployment on board RV Sonne.

The streamer is a modular digital seismic array (HTI, High Tech, Inc.) which can be operated in water depths up to 6000 m. It consists of a 50 m lead-in cable towed behind the side scan

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sonar fish and single modules for each channel. Two different modules - acoustic and engineering modules - exist (Fig. 1). Each acoustic module houses a single hydrophone and a low- and high-cut filter, preamplifier and 24-bit AD converter in a pressure vessel. Special engineering modules additionally include a compass and pressure sensor which provide information on the depth of the module below sea surface and on its geographical position (heading).

Modules are interchangeable and can arbitrarily be connected by cables of 1 or 6.5 m length (Fig. 1). Up to 96 channels can be combined.

Selectable sample intervals and preamplifier gains between 0.25 - 500 ms and 0 - 36 dB, respectively and two different high-pass filters with 4 Hz low-cut frequency allow to use different and sufficiently high-frequency seismic sources to guarantee both a very high vertical and lateral resolution. At this stage of development the streamer consists of 26 modules including three engineering modules.

phical position (latitude, longitude) of each streamer node at each shot/trigger time. Gyro compass and motion sensor data from the ship and, possibly first break and multiple arrival times contribute to this program, indirectly.

During seismic profiling the shot table is stored on hard disc and thus serves as a log file which allows to assign the exact source and receiver geometry to the seismic data header later offline, for subsequent data processing steps.

The exact depth and position of the side scan sonar fish is determined by the ultra-short base line (USBL) system POSIDONIA. It mainly consists of an acoustic array (antenna) installed in the moon-pool and calibrated for its particular position, and a responder mounted on the side scan sonar fish and housing a pressure transducer. The responder function is triggered via cable link through a linux-based gateway PC into the coaxial or fibre optic sea cable by interrogations from the POSIDONIA cabinet.

Together with DGPS, gyro compass and motion sensor information provided by the ship the POSIDONIA system allows to determine the depth and position of the side scan sonar fish with an absolute accuracy of 1% of the water depth.

The seismic are stored underwater on the linux-based PC and are transmitted via ethernet to an on board PC running a GEOMETRICS Strata Visor quality control and data storage program. Two DLT devices are connected for an inifite data storage in daisy chain operation.

Commands which control seismic recording parameters like sample interval, record length, delay or preamplifier gain, and which initialize the data transfer between underwater and on board systems, are sent from the top to the bottom side via low-speed downlink, whereas seismic and side scan sonar data are transferred from the underwater to the top side via telemetry and high-speed uplink through a coaxial (RV Meteor) or fibre optic sea cable (RV Sonne). Laboratory tests with a 5 and 11 km long coaxial cable, and experiences gained during the INGGAS test cruise SO162 with RV Sonne have yielded sufficiently high data transfer rates (500 - 800 kByte/s) so that almost all complete shot gathers could be transferred online from the bottom to the top side system during seismic profiling, allowing an online quality control of the complete data set.

The depths, geographical positions and heading values determined by the ultra-short base line (USBL) system POSIDONIA and the three engineering modules of the digital seismic streamer are fed into a navigation program.

Together with the DGPS based trigger times this program generates a shot table which provides information on the depth and geogra-

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The deep tow seismic streamer and side scan sonar system can be completely controlled from the top side by a linux-based gateway PC. At the bottom side a second linux-based PC with 120 GB storage capacity and a telemetry system, which handles the data transfer between underwater and on board systems and provide all necessary power supplies for the bottom electronics, are installed in a pressureproofed housing mounted on the side scan sonar fish.

All bottom and top side components and air gun shooting are synchronized by DGPS timebased trigger signals generated by the linux gateway PC. Additionally, all components controlling the deep tow device are linked via ethernet and form a small PC cluster within the computer network on board the research vessel during each cruise.

The deep tow system has recently (21.02. 12.03.02) been tested in the Yaquina Basin off Peru during RV Sonne cruise SO162 (INGGAS Test). A GI-gun of 0.7 l volume and a Praklatype airgun of 1.6 l volume were used as highfrequency seismic sources. The first test profile, run along the strike of the Peruvian continental margin in order to keep maneuvring of the 75 m long (50 m lead-in, 25 1 m long cables) deep-towed streamer as simple as possible, showed a very high data quality and resolution of the subsurface structures on the on-line display. Observation of the depth (and heading) data provided by the engineering modules showed a good agreement with the depth data determined by the POSIDONIA system for the side scan sonar fish and only slight depth variations along the streamer length, so that an accurate online control of the streamer position is possible.

profiling yielded that a preamplifier gain of 12 dB is optimum for the high-frequency small chamber sources used during this test cruise.

A final survey along a grid of 11 closely spaced profile lines covering an area where the "Max and Moritz" chemoherms were discovered during RV Sonne cruise SO146 (GEOPECO) proved that the complete deep tow system can be handled for such high-resolution 3D surveys. Turns from one profile line to another of about 600 m diameter could be operated so that distances of about 100 m between neighbouring profile lines could be reached by an appropriate survey design. The seismic data recorded along these lines show a very detailed image of the chemoherms in this area.

Variations of the ship velocity between 1.0 and 4.0 kn demonstrated that the best results with the lowest noise level could be achieved for a velocity of 3.0 kn. If the stability of the side scan sonar fish and the reach of the acoustic side scan sonar signals are simultaneously taken into account velocities up to 3.5 kn are also acceptable at an optimum towing depth of 80 - 120 m above the sea floor.

A loss or severe distortions of the seismic signals observed during winch operations and during turns from one profile line to another could be identified as an overload of the preamplifiers caused by "fast" changes in water depth. A subsequent check of the gains actually required during smooth normal seismic

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In-Situ Characterization of Gas Hydrates Brückmann W. (1), Linke P. (1), Mörz T. (1), Türk M. (1), Poser M. (2) (1) GEOMAR Forschungszentrum für Marine Geowissenschaften, Kiel, Germany (2) Oktopus GmbH, Hohenwestedt/Kiel, Germany

An important issue in current gas hydrate research is the need for better tools to remotely estimate of the volume of marine gas hydrate in the near subsurface. Improving these estimates is of critical importance for determining the global abundance of gas hydrate, for evaluating their importance for the stability of continental slopes and their potential for economic exploitation.

Our knowledge about the occurrence, spatial distribution, and life-cycle of gas hydrates in marine sediments is mainly derived from indirect geophysical and geochemical evidence.

Namely pore water freshining, i.e. the degree of Cl-depletion in interstitial water of marine sediments can be used to get a first-order estimate of hydrate abundance. In a few instances gas hydrates have also been directly observed or even sampled at the sea floor, e.g. at Hydrate Ridge off the Oregon coast and in mud volcanoes in the Black Sea. For regional or global estimates of hydrate volumes however, new techniques for ground-truthing and calibration of geophysical and geochemical methods are needed.

As part of Cooperative Research Center (SFB) 574 "Volatiles and Fluids in Subduction Zones" a new tool, HDSD (Hydrate Detection and Stability Determination) is being developed to address this issue. HDSD is designed to identify and quantify small volumes of near-surface gas hydrate through continuous in situ thermal and resistivity monitoring in a defined volume of sediment while it is slowly heated to destabilize gas hydrates embedded in it.

In its current configuration HDSD is delivered to the seafloor with a video-guided GEOMAR BC Lander system. The sediment volume to be tested for the presence and abundance of gas hydrates is first isolated by a rectangular experiment chamber that is pushed into the

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upper 30cm of sediment.

A “stinger”, centrally mounted in the chamber and equipped with two arrays of sensors, provides the capability for monitoring the sediment resistivity and temperature profile during the test. A computer-controlled electric heating system and heat-exchange unit mounted on top of the chamber provides the means for transferring energy into the sediment.

In its initial configuration HDSD will be operating over a 24 to 36 h period in a twostep mode: after insertion the sensors will first be used to collect the undisturbed resistvity and temperature profile. During the second phase a pre-programmed heating cycle is carried out to slowly destabilize any gas hydrate contained in the volume. The sensor array is used to monitor the migrating temperature wave and the change in pore fluid resistivity resulting from hydrate breakdown.

This data together with well constrained initial PT conditions at the test site will be inverted in a thermodynamic phase model to yield the volume and distribution of gas hydrate.

The HDSD tool will be first deployed and tested in July 2002 during RV SONNE cruise 165 (OTEGA) to Hydrate Ridge, were gas hydrates are abundant in the shallow subsurface. For the next stage of development additional sensors will integrated into the chamber to provide enough data for resistivity tomography.

Gas hydrate reservoir characterization using multi-component wide-angle and ocean bottom cable seismic data Bünz S., Mienert J., Andreassen K. Department of Geology, University of Tromsø, Dramsveien 201, 9037 Tromsø, Norway

Summary Ocean Bottom Seismometer and Ocean Bottom Cable data allow to assess the elastic properties of hydrated and gassy sediments in an integrated approach. The study area is located north of the Storegga Slide sidewall in 800 m – 1200 m water depth. Our data indicates variable concentrations of gas below the gas hydrates, which might result in locally confined zones of overpressure. Gas hydrates appear to occur in disseminated form and in low concentrations, which do not allow cementing the sediment grains.

Introduction Understanding the distribution and concentration of marine gas hydrates is necessary to assess its role in slope stability, controlling global climate and as a possible future energy resource. Research in other areas indicates that multi-component studies together with additional geotechnical data seem to be the best approach to study the nature of this reservoir (Guerin and Goldberg, 1999). Geophysical evidence for gas hydrates exists along the northern sidewall of the Storegga Slide (Figure 1) (Mienert et al., 1998, Andreassen et al., 2000). A BSR reflects the base of the Gas Hydrate Stability Zone (GHSZ), and the free gas zone beneath it. High-resolution seismic data above the hydrated sediments reveals that the BSR amplitude is variable and in some places the BSR is only identified as an abrupt termination of high-amplitude reflections underneath. Such high-amplitude reflections are interpreted as strata-bound free gas, which accumulates beneath less permeable layers (Bouriak et al, 2000). Results from the ocean

bottom cable data so far indicate that gas hydrate do not cement the sediment (Andreassen et al., 2001). Furthermore there is no reflection from the gas below the hydrates, which points towards low gas concentrations.

Seismic data In this approach we commence a high-resolution evaluation of Vp/Vs-ratio and shearwave velocity of the converted wave records from a 4 km long ocean bottom cable line and from 4 ocean bottom seismometer stations (Figure 1). The P-S data evaluation requires a special processing procedure to determine the Vp/Vs-ratio and the shear-wave velocity of the sediments. To couple the converted-wave velocities to the determined p-wave velocity model, a different approach was applied using a quasi Vp/Vs semblance method. In this approach velocities of the converted waves were calculated from the p-wave model using fixed Vp/Vs ratios. The resulting non-hyperbolically moveout-corrected gathers were stakked to a single trace for each Vp/Vs-ratio. The resulting traces were plotted as a seismic section. Within these sections the Vp/Vs ratio varies from 1.7 to 7.7. Highest energies in such section occurs for Vp/Vs ratios for which the arrivals stack best. The results from this technique provide the starting models for raytracing and amplitude modeling.

Results and discussion The compressional-wave velocity shows a distinctive increase just above the BSR and a low-velocity zone below the BSR. We interpret these zones to be caused by hydrated and gascharged sediments, respectively. Another low-

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BSR. Gas seems to be distributed heterogeneously below the gas hydrates, as already indicated by the enhanced reflections. Gas hydrates act as a seal and continued accumulation of the trapped gas possibly leads to local zones of undercompaction and overpressure. Such overpressure would reduce the effective stress and grain coupling leading to low shear modulus and low shear-wave velocity.

Conclusion - Heterogeneous distribution of gas occurs below the sealing gas hydrates.

- Gas hydrate does not contribute to the cementing of the sediments and its concentration seems to be low.

Figure1: Location of the study area and data coverage.

velocity zone occurs at about 250 m below the BSR, at the base of the Naust Formation. This is the upper termination of a polygonal fault system and the base of a fluid leakage system in the area. The magnitude of the velocity decrease, i.e. 200 â&#x20AC;&#x201C; 300 m/s, is caused by free gas. The Vp/Vs-ratio decreases through the whole sediment column from 7 for the uppermost sediments to 5 at the depth of the BSR. It shows a positive deviation from its downward decreasing trend associated with the p-wave low-velocity zone just below the BSR. At some locations this anomaly is stronger and seems to correlate with enhanced reflection just below the BSR. We believe that this indicates the occurrence of gas of higher concentrations underneath the hydrates. Further downward, the Vp/Vs-ratio continues to decrease to values of about 3 at a depth of 600 m below seafloor. The second gascharged layer at about 500 m depth is not detected by the shear waves. One of the premier applications in offshore industry of recording shear waves is to image through gas clouds. Whereas shear waves behave exemplary for the lower gas-charged layer in our case, they do not so for the gas that occurs beneath the

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References Andreassen, K., Mienert, J., Bryn, P. and Singh, S. C., 2000. A double gas-hydrate related bottom simulating reflector at the Norwegian continental margin. Annals Of The New York Academy Of Sciences 912, 126-135.

Andreassen, K., Berteussen, K. A., Mienert, J., Sognnes, H., Henneberg, K. and Langhammer, J., 2001. Investigating gas hydrates using seismic multi-component ocean bottom cable data.

Extended abstract, EAGE 63rd conference & technical exhibition, Amsterdam, The Netherlands, 11 â&#x20AC;&#x201C; 15 June.

Bouriak, S., Vanneste, M. and Saoutkine, A., 2000. Inferred gas hydrates and clay diapirs near the Storegga Slide on the southern edge of the Voring Plateau, offshore Norway. Marine Geology 163(1-4), 125-148.

Guerin, G., Goldberg, D. and Meltser, A., 1999.

Characterization of in situ elastic properties of gas hydrate-bearing sediments on the Blake Ridge. Journal Of Geophysical Research-Solid Earth 104(B8), 17781-17795.

Mienert, J., Posewang, J. and Baumann, M., 1998.

Gas hydrates along the northeastern Atlantic Margin; possible hydrate-bound margin instabilities and possible release of methane. Geological Society Special Publications 137, 275-291.

Gas hydrate formation and dissolution experiments in a pressure chamber Drews M. (1), Holscher B. (2), Gust G. (2), Wallmann K. (1) (1) GEOMAR Research Centre for Marine Geosciences, Wischhofstrasse 1 - 3, 24148 Kiel, Germany (2) Ocean Engineering 1, Technical University Hamburg-Harburg, 22305 Hamburg, Germany

We started first experiments on the formation and dissolution of methane gas hydrates in a deep sea simulation chamber (APROACH, adaptive pressure ocean analysis chamber) constructed by the Technische Universität Hamburg-Harburg (TUHH), Department of Ocean Engineering 1.

Up to now the kinetics of gas hydrate dissociation was mainly studied in the context of technical applications, where gas hydrates are destabilised when temperature increases, pressure decreases, or when chemical agents attack and destroy the hydrate matrix (Sloan Jr., 1998). The process of gas hydrate dissociation through contact with methane-undersaturated bottom water, which controls abundance, distribution, and dissolution of gas hydrates outcropping from the sea floor, has only recently been studied in an in situ experimental setup, which used a remotely operated vehicle transporting methane gas hydrate pieces through the water column (Rehder et al. in prep.). Until now, there have been no attempts to measure gas hydrate dissolution rates and kinetics under possibly changing salinity or methane concentrations of the sea water in the laboratory.

The newly designed pressure chamber of the TUHH provides the possibility to study gas hydrate formation and dissolution under almost realistic conditions. The pressure chamber consists of an pressure-stable cylindrical liner equipped with an inspection window for optical observation, a base plate with split connectors, a crane, the pressure pump and a cryostat (Figure 1). Pressure (0–500 bar) and Temperature (1–25 °C) are selectable and can be monitored online with standard data

processing equipment. During first experiments we were able to synthesise methane gas hydrate in salt water (Figure 2) and subsequently watch its dissolution. The dissolution rates of gas hydrate will be calculated from high precision conductivity measurements, using an enhanced sensor (originally from a CTD-probe, K.U.M., Kiel).

During gas hydrate formation in the inner reaction vessel ion exclusion is responsible for a salinity increase in the surrounding sea water, whereas dissolution leads to a salinity decrease.

Figure 1: Deep sea simulation pressure chamber constructed by the Technische Universität Hamburg-Harburg, Department of Ocean Engineering 1.

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Figure 2: Methane gas hydrate formed at 1 째C and 90 bar at the gas phase water boundary in the inner reaction vessel of the pressure chamber.

References Rehder, G., Kirby, S. H., Durham, W. B., Stern, L., Peltzer, E. T., Pinkston, J., and P. G. Brewer (in prep.): Dissolution rates of pure methane hydrate and carbon dioxide hydrate in undersaturated seawater at 1000 m depth.

Sloan, Jr., E., D. (1998): Physikal/chemical properties of gas hydrates and application to world margin stability and climate change. In: Gas Hydrates: Relevance to World Margin Stability and Climate Change, Vol. 137 (ed. J.P. Henriet and J. Mienert), pp. 31-50. Geological Society.

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Microbiological and geochemical investigations at gas hydrate sites in the Black Sea Drews M. (1), Schmaljohann R. (2), Aloisi G. (1), Wallmann K. (1) (1) GEOMAR Research Centre for Marine Geosciences, Wischhofstrasse 1 - 3, 24148 Kiel, Germany (2) Institut für Meereskunde (IFM), University of Kiel, Düstenbrooker Weg 20, 24105 Kiel, Germany

At station 18-TGC, approximately 1.5 km east of the Odessa mud volcano (44°21.01 N, 35°09.28 E) in 1936 m water depth, we obtained a gravity core which contained gas hydrates and bacterial mats attached to carbonate crusts. This core was studied in great detail with respect to geochemical analyses (pH, sulfide, sulfate, methane, alkalinity, and ammonia concentrations in the pore water, Figure 1) and microbiological activity measurements.

The boundary in approximately 20 cm depth between light grey hemipelagic mud and a black sapropel layer consisted of a 2 cm thick carbonate crust associated with a bacterial mat.

The pores of the crust were filled with stiff gelatinous white to pink bacterial colonies. The sulfate concentration decreased in a sharp gradient from bottom water values (17.6 mM) to 1– 1.6 mM in about 20 cm sediment depth, where crust and mats were located. Likewise, sulfide decreased from highest concentrations in the surface layer (4 mM) in a steep gradient. This strongly hints on intensive bacterial sulfate reduction. As a consequence of anaerobic methane oxidation, which is mediated by the sulfate reduc-

tion (CH4 + SO42– ¢HCO3– + HS– + H2O), the hydrogen carbonate concentration and therefore the total alkalinity shows highest values (16 mM) just above the crust. Carbonate precipitation is caused by the production of carbonate alkalinity during anaerobic methane oxidation (Ca2+ + 2HCO3– ¢ CaCO3( ) + CO2 + H2O).

High quantities of small gas hydrate pieces were found in two strata. The dissociation of gas hydrate during sampling becomes apparent by very high methane concentrations in the whole core, and in particular in peak concentrations in the same layers as the gas hydrates occurrences. Measured methane profiles are therefore largely artifacts and do not represent in situ methane concentrations. The dissociation of gas hydrate during core retrieval also leads to the dilution of pore water measured as a decrease of the chloride concentration. Further, the very low temperature of the sediment measured on deck (0.7 °C) compared to the in situ bottom water temperature (9 °C) is a consequence of the endothermic dissociation reaction.

At TV-grab station 8-TVG in 1874 m depth at the south western flank of the Odessa mud volcano (44°22.97 N, 34°08.50 E) we could continue the sampling of carbonate crusts and associated bacterial mats. The grabbed material consisted of dark grey hemipelagic mud and crusts. A different type of bacterial mat, brownish to yellow and slimy, appeared when the sediment was retrieved on deck. Below the carbonate crust sediment pieces showed a coating with a stiff mucus-like bacterial mat being attached to the sediment fracture walls.

This gave the idea of filled passages or channels which released the slimy substance when torn open. The sediment was characterised by ¢

We present first microbiological and geochemical results obtained during the METEOR cruise 52-1 from sediments at the Odessa and Yalta mud volcanos in the Sorokin Through in the northern Black Sea at water depths about 1800–2100 m. The geochemical characteristics of the sediment (anoxic and sulfidic conditions, gas hydrate occurrences 1 m below the sea floor) where bacterial mats associated with carbonate crusts occur, is a strong indication that these mats are responsible for anaerobic methane oxidation mediated by sulfate reduction.

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sulfide concentrations of 1.5 mM and ammonia concentrations of 80 µM. High sulfate reduction activity was indicated by very low sulfate concentrations (0.3–2.6 mM). The alkalinity reached a very high value of 14 mM. On the central mound of the Yalta collapsed mud volcano in 2124 m water depth at station 59-TVG (44°14.54 N, 34°47.11 E) we found impressive 2 to 4 cm thick bacterial mats attached to carbonate crusts, which resembled the thick mats discovered in shallower water depths (above the gas hydrate stability field) during the Professor Logachew cruise in summer 2001, and which grow on carbonate chimneys where methane gas bubbles surge into the water column (GHOSTDABS project).

The bacterial mats discovered during our cruise were probably of the same type Pimenov et al. (1997) described as coral-like structured, overgrowing aragonite crusts in water depths of 150–190 m in the north western shelf methane seep area in the Black Sea. Activity measurements combined with microscopic and radio isotopic investigations revealed anaerobic methane oxidation.

Reference Pimenov, N. V., Rusanov, I. I., Poglazova, M. N., Mityushina, L. L., Sorokin, D. Y., Khmelenina, V. N. and Trotsenko, Y. A. (1997): Bacterial mats on coral-like structures at methane seeps in the Black Sea. Microbiology, 66 (3): 354– 428.

Figure 1: Pore water chemistry of station 18-TGC approximately 1.5 km east of the Black Sea Odessa mud volcano in 1936 m water depth. The top bar marks the zone where carbonate crust and bacterial mat occurred, the two lower bars mark the main gas hydrate zones.

Figure 2: Bacterial mat grown on carbonate crust pieces of up to 30 cm length were found at station 59-TVG (Yalta mud volcano in the Black Sea).

The 2 to 4 cm thick mats were of a yellow to orange or pink colour and consisted of a stiff gelatinous fabric.

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Authigenic Carbonates in a Cold Seep Environment: Sensitive Recorders of Rapid Anoxia and Sealevel Changes Determined by U- and Th-isotope Measurements (LOTUS) Eisenhauer A., Teichert B.M.A., Bohrmann G., Liebetrau V., Linke P. GEOMAR, Forschungszentrum für Marine Geowissenschaften, Wischhofstr. 1-3, 24148 Kiel, Germany

Uranium (U) and Thorium (Th) concentrations and activity ratios (δ234U; 230Th/234U) are precise geochronometer and sensitive recorders of the redox conditions at submarine seeps of hydrocarbon-rich fluids at Hydrate Ridge, off the coast of Oregon ('cold seeps'). The low U concentrations but relatively high δ234U values of gas hydrate carbonates reflect sedimentary pore water indicating that they were formed under anoxic conditions below or at the sedimentary surface. Their (230Th/ 234U)-ages span a time interval from 0.82 to 6.34 ka and cluster around 1.24 and 4.71 ka. This is interpreted as to reflect time intervals of intense CH4 flux and microbiological activity as well as gas hydrate formation.

In contrast, chemoherm carbonates precipitate from marine bottom water. However, their δ234U-ratios as well as the δ234U-ratios of the bottom water are enriched in 234U relative to normal seawater. Mass balance calculations reveal that this enrichment reflects a contribution of about 10 % of U from sedimentary pore water to the bottom water and the chemoherm carbonates, respectively.

234 U/230Th ages of chemoherm carbonates (e.g.

South East Knoll) vary in between 7.33 and 267.72 ka and tend to correspond to time intervals of low sealevel at glacial climatic stages (2, 4, 6, 8) and interstadials (7d). Latter observation is confirmed by the measurement of stable oxygen isotopes (δ18O) which tend to be enriched in the heavy isotope as it is expected for carbonate formation during low sealevel positions. Following this observation, we propose that long-term fluctuations of fluid

flow rates from hydrocarbon seepages are controlled by the pressure difference between the seawater column and the plumbing system below the seepages. When sealevel is relatively high (during warm climatic stages) the hydraulic pressure of the water column may exceed the pressure of the plumbing system below the cold seeps. Then, no fluid flow occurs at cold seep areas. In contrast, when sealevel is relatively low the hydraulic pressure of the plumbing system may exceed the pressure of the water column. Then, fluid flow occurs and triggers chemoherm carbonate formation.

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Experimental determination of physical and physico-chemical properties of gas hydratebearing sediments (Project 555A - Overview) Erzinger J. (co-ordinator), Spangenberg E., Schicks J., Naumann R., Lüders V., Möller P., Kukowski N. GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany

The overall objective of the project is to achieve a better understanding of the thermodynamic and kinetic behavior of mixed gas hydrate systems and the physical properties of gas hydrate-bearing sediments by means of an interdisciplinary research program combining geophysical, mineralogical, geochemical, and crystallographical approaches.

An experimental program has been started to simulate natural conditions of hydrate formation. The expected results will allow more reliable evaluation of methane energy resources, provide an improved basis for calibrating physical properties which can be estimated in situ, and also provide data for numerical modelling of reservoir dynamics. A better knowledge of the stability of pure (CH4, CO2, N2) and mixed clathrates in the system CH4-CO2-N2-H2S-H2O is necessary in order to reach the goals of this project.

The detailed objectives are: 1) To optimise and refine the newly-installed gas hydrate-sediment experimental apparatus for synthesis of natural gas hydrates of the structure type ”sI” in porous media.

2) To determine the influence of sediment structure on the formation and dissociation of gas hydrates as well as on their texture and distribution.

3) To determine seismic velocities and electrical properties of sediments as a function of gas hydrate content, composition and structure.

4) To determine how texture, distribution and grain size of gas hydrate bearing sediments control hydraulic permeability.

5) To determine physical and thermodynamic properties of mixed clathrates in the system CH4-CO2-N2-H2S-H2O and the influence of

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gas fractionation on the formation of methane hydrates.

Hydrate-sediment experimental apparatus; low-temperature XRD sample chamber The experimental apparatus was first applied to the synthesis of gas hydrates in the absence of a sedimentary matrix. The crystallization of hydrates from aqueous fluid with dissolved methane required strong undercooling, and the rate of reaction was much lower than expected and described in the literature. To avoid these problems we developed an alternative procedure whereby fine ice crystals were slowly heated to the melting point in a methane atmosphere (p>100 bar). Under these conditions, the reaction 5.75H2O(solid) + CH4(gas) ¢ CH4 • 5.75H2O ran to completion within about one week. The pure methane hydrates was used to calibrate a big volume calorimeter and the low-temperature X-ray diffraction apparatus.

Synthetic hydrate-bearing "sandstone" of known composition was prepared by compressing mixtures of powdered methane hydrate with ice and sand in a cold methane pressurized piston-cylinder cell. This material was used to test the FLECAS (Field Laboratory Experimental Core Analysis System) which was developed for the project "In-situ Gas Hydrate Laboratory – Mallik Research Well".

In addition, we continued with theoretical modelling of physical properties of hydrate bearing sediments.

Technical details of the experiments and first results will be given as poster presentations (#20 and #22) by Kulenkampff, Spangenberg, Naumann and Spangenberg, Kulenkampff, respectively (for details see contributions in this volume).

The structural studies required the construction of a special low-temperature X-ray diffraction sample chamber, which was commissioned at the start of the project and delivered in the summer of 2001. Initial technical problems with the controller unit and software were overcome, and an operational problem of ice building up on the sample holders during test runs at -100°C was solved by flushing the chamber with cooled dry gaseous nitrogen. After these modifications, the first successful tests have shown that we can perform crystal structure analysis of gas hydrates using this comparatively simple and cost-effective equipment.

Determining p-T-x phase relations of pure and mixed gas hydrates A specially designed cooling stage mounted on a petrographic microscope was set up in 2000 which allows observation of hydrate formation and dissociation in transmitted and reflected light under controlled conditions of temperature, pressure and gas composition. This first prototype was able to deliver a temperature precision of ± 2°C over the range of -18 to +80°C. A second stage was built in 2001 which has a greatly improved temperature precision of ± 0.1°C in the range -27 to +80°C, but allows observation only in reflected light.

Both stages can be operated with a Raman spectrometer, as well. Phase diagrams for the methane-water system have been determined using this equipment and these show excellent agreement with literature data. The first results of the actual measurements on the system CH4 – CO2 – H2O will be presented orally by Schicks, Lüders, and Möller (for details see contribution in this volume).

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The role of gas hydrates in the course of rapid climate changes - Isotopic studies on methane in polar ice cores Fischer H., Richter K.-U. Alfred-Wegener-Institute for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany, hufischer@awi-bremerhaven.de

Summary Focus of this project is the identification of the sources responsible for changes in the atmospheric methane concentration during rapid climate changes in the past and here especially the role of a potential destabilization of methane hydrates. To this end isotopic measurements of methane will be performed on air samples extracted from a northern Greenland ice core covering the complete last glacial cycle using a new gas chromatography mass spectrometry method. The development of this method enables for the first time to perform high precision carbon and hydrogen isotopic measurements on very small ice core air samples and using the isotopic signature of methane to constrain the sources responsible for paleoclimatic methane variations in the atmosphere.

Background Bubble enclosures in polar ice cores represent the only direct atmospheric archive for the reconstruction of paleoatmospheric variations in methane concentrations over up to the last 500,000 years. Previous ice core studies showed an extraordinary close coupling of atmospheric methane concentrations and isotope temperatures as reconstructed from Greenland ice cores (Fig. 1). The long-term trend in methane shows an increase from concentrations below 400 ppbv during the last ice age up to a level of 700 ppbv during warm climate periods [Raynaud, 1993]. Starting at about 1750 AD a clear anthropogenic increase to concentrations of more than 1700 ppbv could be detected [Etheridge et al., 1998]. In addi-

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tion to these long-term changes very strong increases in the atmospheric methane concentration of about 200 ppbv occurring over a few decades to centuries were found in parallel to rapid climate variations in the northern hemisphere (Dansgaard-Oeschger events, Younger Dryas) during the last glacial [Chappellaz et al., 1993].

The contributions of different sources to these changes in atmospheric methane concentrations and here especially the role of gas hydrates are not unambiguously known so far. In this respect a climate induced destabilization of marine methane hydrate stocks as well as the release of methane bound in permafrost regions could represent a major player during rapid climate warming events. A first approach to distinguish different geographic methane source regions is based on the interpretation of the interhemispheric gradient in methane concentration (as determined on Greenland and

Figure 1: Isotope temperature and methane profile of the GRIP ice core, central Greenland

Antarctic ice cores). The results of this approach point to a strong source in middle and high northern latitudes at the beginning of the Holocene, as expected for a methane release from thawing permafrost [Chappellaz et al., 1997]. However, in the course of rapid climate variations such a gradient can not reliably be determined.

Here, the isotopic composition of methane represents an unique tool to distinguish different methane sources and to quantify the global methane budget in more detail (Fig. 2). The carbon isotopic composition enables to distinguish thermogenically and recently bacterially produced methane. Furthermore, the hydrogen isotopic composition allows for a distinction of different bacterial pathways, hence the milieu in which the bacterial methane production takes place (marine vs. terrestrial) (Fig. 2).

In addition, the reaction of methane with OH radicals, representing the major sink of methane in the atmosphere, results in an enrichment of the heavier methane isotopes in the atmosphere. Thus, the reconstruction of paleoclimatic changes in the isotopic composition of atmospheric methane can contribute distinctively to assign the relevant source processes to the observed concentration changes during Dansgaard-Oeschger events and the last glacial/interglacial transition.

Objectives In order to answer the question of the origin of variations in atmospheric methane concentrations during rapid climate changes, carbon (and in a second step also hydrogen) isotopic measurements on methane in ice core air bubbles will be performed on the North-GRIP ice core, drilled in the years 1998-2001 in northern Greenland. The measurements will focus on investigations on selected DansgaardOeschger events, the Holocene/Pleistocene transition (Younger Dryas, Bølling-Allerød oscillation), the last glaciation and for validation of the method on recent ice. Due to the very large sample size required for such analyses so far (25 kg of ice), previously published values of the methane isotopic composition

from ice cores are restricted to a pilot study by Craig et al. [1988]. To lower the detection limit significantly we are currently developing a new gas chromatography isotope ratio monitoring mass spectrometry (GCirmMS) method [Merritt et al., 1995] both for δ13C and δD in CH4. This method reduces the necessary sample size to 10-50 ml STP (equivalent to 100500 g of ice). Test measurements of δ13CH4 in 20ml air samples using this method showed a reproducibility of 0.1‰. For the analyses of ice core air samples a melt extraction is currently developed, which warrants the complete extraction of air from bubble enclosures in the ice.

Figure 2: Isotopic signature of different methane sources compared to the atmosphere [Whiticar, 1993]

In a second step an online preparation method for hydrogen in methane will be established. In summary, after completion of the technical 13 developments a method for direct δ C and δD analyses on methane in very small air sample is available for the first time, which will also allow to perform comparable isotopic studies in other geoscientific fields.

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References Blunier, T. and E.J. Brook, Timing of millenialscale climate change in Antarctica and Greenland during the last glacial period, Science, 291, 109-112, 2001.

Chappellaz, J., T. Blunier, S. Kints, A. D채llenbach, J.-M. Barnola, J. Schwander, D. Raynaud, and B. Stauffer, Changes in the atmospheric CH4 gradient between Greenland and Antarctica during the Holocene, Journal of Geophysical Research, 102 (13), 15987-15997, 1997.

Chappellaz, J., T. Blunier, D. Raynaud, J.M. Barnola, J. Schwander, and B. Stauffer, Synchronous changes in atmospheric CH4 and Greenland climate between 40 and 8 kyr BP, Nature, 366, 443-445, 1993.

Craig, H., C.C. Chou, J.A. Welhan, C.M. Stevens, and A. Engelkemeir, The isotopic composition of methane in polar ice cores, Science, 242, 1535-1539, 1988.

Etheridge, D.M., L.P. Steele, R.J. Francey, and R.L. Langenfelds, Atmospheric methane between 1000 A.D. and present: Evidence of anthropogenic emissions and climatic variability, Journal of Geophysical Research, 103 (13), 15979-15993, 1998.

Merritt, D.A., Hayes, J. M., Des Marais, D. J., Carbon isotopic analysis of atmospheric methane by isotope-ratio-monitoring gas chromatography-mass spectrometry, Journal of Geophyiscal Research, 100 (D1), 1317--1326, 1995.

Raynaud, D., Jouzel, J., Barnola, J. M., Chappellaz, J., Delmas, R. J., Lorius, C., The ice core record of greenhouse gases, Science, 259, 926--934, 1993.

Whiticar, M.J., Stable isotopes and global budgets, in Atmospheric methane: sources, sinks, and role in global change, edited by M.A.K. Khalil, pp. 138-167, Springer, Berlin, 1993.

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INGGAS-Flux: New tools for energy and fluidflux: pore pressure and thermal gradient probes Gennerich H.-H., Grevemeyer I., Kaul N., Villinger H. Fachbereich Geowissenschaften, Universität Bremen, Postfach 330 440, 28213 Bremen, Germany

Two different tools are designed and tested within this INGGAS subproject: 1. a 6m long heat flow probe to expand measurement capabilities from deep sea environments to shallow water (continental margins) in order measure reliable sediment temperature gradients in the presence of bottom water temperature variations 2. a pore pressure tool to measure in situ pore pressures in sediments in order to quantify fluid flow. This second tool is split into two units: a) the data acquisition unit and b) an autonomously operating data transmission buoy.

1 Heat flow probe The new heat probe is capable to measure temperature gradients and in situ thermal conductivity in sediments to determine terrestrial heat

flow. The large penetration depth of 6m, twice as deep as normally used instruments is necessary to get reliable results in water depth of less than 2000m where varying bottom water temperatures create transient temperature disturbances in the subsurface. This is very often the case for heat flow surveys over gas-hydrate bearing sediments at continental margins. The mechanical design of the probe follows the violin bow concept and is adapted in size and material strength to the desired maximum penetration depth. Numerical modeling of the dimensions of sensor string and strength member assisted in the final design. The data acquisition in the instrument is normally under realtime control from a deck unit on board the research vessel but can also be operated in a completely autonomous way if no suitable cable is available on board.

Data acquisition unit (in heat probe at seafloor)

Data logger for • Signal conditioning of analogue temperature signal • A/D conversion with 22 bit resolution • Data storage • Control of heat pulse for in situ thermal conductivity measurement • Data acquisition and storage of penetration monitoring sensors (pressure, tilt, acceleration, altimeter) • Real-time communication with deck unit through coax deep sea cable • Temperature range of –2 to 70 °C • Temperature resolution of < 1mK from –2 ° to 12 °C • Battery and storage capacity allow continuous operation for 3 days • Operational up to 6 km water depth

Deck unit (on board research vessel)

PC for: • Data capture and storage on hard disk • Control of the instrument at the seafloor • Communication with the instrument at the seafloor through coax deep sea cable • Real-time graphical display of data

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The data acquisition system including the communication package is designed and built by an industry partner according to our specifications. The complete mechanical system is shown in Figure 1. A first sea trial will take place during M54/2 off Costa Rica in August/September 2002.

2 Pore pressure tool The goal is to detect vertical fluid flow within seafloor sediments with rates as low as 1 mm/a. This will be achieved by measuring pore pressures in the sediments at various depths for a maximum period of two month with a minimal time resolution of 10 minutes to monitor tidal and other low frequency effects.

We decided to employ one differential pressure transducer and three subsurface pressure ports using a hydaulic multiplexer. Operation of the hydraulic multiplexer has been tested in the laboratory and under deep ocean pressure condition in a pressure chamber as well. After free-falling to the seafloor the instrument records pressures over a preset time window and the data are transfered to the satellite communication unit. This unit will surface after the end of the measurement period and send the data to shore via an IRIDIUM satellite link.

The complete system is designed as expendable system to save additional ship time cost for recovery of the data. A sketch of the system design is shown in Figure 2.

Data acquisition unit (pore pressure measurement)

Data logger for • Signal conditioning of analogue differential pressure signal • A/D conversion with 22 bit resolution • Data storage • Data acquisition and storage of environmental parameters (tilt, temperature) • Data transmission to satellite communication unit • Battery and storage capacity allow continuous operation for 2 months • Operational up to 6 km water depth

Satellite communication unit

• • • •

Storage of pressure and environmental data Timing release Data compression Transmission of complete data set through IRIDIUM satellite link

The satellite communication system is designed and built by an industry partner according to our specifications. The complete mechanical system is shown in Figure 2. A first sea trial will take place at the end of March 2002 in the Baltic Sea. A second test is scheduled for October 2002.

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Figure 1: New heat probe with total length of 8,1 m and a minimum total weight of ca. 900kg.

Figure 2: Sketch of the expendable differential pore pressure probe. The data transmission unit is a self-contained satellite data transmission link.

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Quantification of dissolved and free methane at gas hydrate associated cold vents: The use of lander and ship mounted hydro acoustic systems and methane sensors Greinert J. (1), Keir R. (1), SpieĂ&#x; V. (2) (1) GEOMAR Research Center for marine Geosciences Kiel, Germany, jgreiner@geomar.de (2) University of Bremen, Germany

Methane hydrates are an important carbon reservoir in the marine environment that are formed from the advection of methane and H2S rich fluids through sediments. Methane hydrates form only when very high concentrations of methane, most likely in the form of free gas, are present at high pressures and low temperatures. Thus gas hydrates are closely linked to free gas emissions from the seafloor into the water column and possibly into the atmosphere, and high methane concentrations are found in the water column near hydrate deposits. Important mechanisms that influence the carbon cycle at cold vents are the biogenic anaerobic oxidation of methane and the precipitation of carbonate.

Similar reactions occur in bacterial mats at the seafloor or within the water column and reduce the methane flux from cold vents.

However, free gas emission in form of bubble streams from the seafloor is suggested to be of major importance for the vertical transport of methane, which may impact regional and global carbon cycles. The amount and periodicity of free gas emissions cannot be investigated by the classical water sample and GC-analyse procedure, which is used to investigate the distribution and fate of dissolved methane.

Gas bubbles such as swim bladders of fish are recognized by hydro acoustic methods, and these bubbles can by quantified. Within Subproject 2 of the LOTUS Project, we are redesigning the PARASOUND hydro acoustic

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system (installed on RV SONNE, RV METEOR and RV POLARSTERN) in order to detect cold vents where gas bubbles escape from the seafloor. In a second step we plan to quantify the gas amount recorded by the 18 kHz signal of the PARASOUND system. Russian scientists have successfully used single beam echo sounders for hydro-acoustic bubble detection in the Black Sea and the Sea of Okhotsk. To obtain an accurate estimate of the volume of gas emitted, a sonar-like hydro acoustic swath system, Gas-Quant, has been developed in cooperation with ELAC-Nautik.

This system will be mounted on a lander and deployed near known gas-emission sites at the Hydrate Ridge (Oregon) for the purpose of recording the distribution of bubble streams, their periodicity and the gas amount.

In addition to 'bubble-detection', the distribution of dissolved methane in the water column will be investigated by classical geochemical methods and with methane sensors (METS) build by CAPSUM. The sensor has been improved and redesigned for long-term deployment on moorings. Water samples will be analysed for the carbon isotopic signal of the dissolved methane and other carbon species with a new mass spectrometer. This will help to distinguish between different methane sources and to investigate methane oxidation rates in the water column.

Both the hydro-acoustic and geochemical investigations will provide strongly needed information about the inventory and oxidation of methane in the water column in regions containing gas hydrates.

Figure 1: The METS mooring system during a test onboard RV ALKOR in October 2001.

Figure 2: Screen shot of 3 gas bubble flares recorded with the modified PARASOUND system onboard RV METEOR January 2002.

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Slope Stability and Land Slides in the Deep Sea: Influence Parameter Gas Hydrates (GASSTAB) Grupe B. (1), Kreiter S. (1), Feeser V. (2), Hoffmann K. (2), Becker H.J. (2), Savidis S. (3), Schupp J. (3) (1) Technische Universität Berlin, Institut für Technischen Umweltschutz, Germany (2) Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften, Germany (3) Technische Universität Berlin, Institut für Bauingenieurwesen, Germany

Decomposition of gas hydrates is thought to be a major cause for the instability of submarine slopes and deep sea floor. The project GASSTAB is focused on the influence of gas hydrates on slope and ground failures from a mechanical point of view. The aim of our investigation has been to establish a base for the theoretical prediction of submarine failure mechanisms.

His scenario was adapted to create a soil mechanical model which is based on two simplifications (Fig. 1b). First the sliding plane shows neither friction nor cohesion and second the model is a 2D profile, assuming symmetrical load distributions.

Possible failure mechanisms of slopes containing gas hydrates were postulated by McIver [1982]. To verify these mechanisms we have analytically computed a discrete model; at a later date we intend to calculate numerical simulations. These calculations must be tightly interconnected with the mechanical behavior of hydrate bearing sediments to understand the processes governing slope and floor failure.

Because there is no or only little soil mechanical data available, a laboratory Gas Hydrate Test System (GTS) for different soil mechanical experiments is under construction.

Sediment samples from the Ocean Drilling Program (ODP) leg 164 were investigated to gain basic data for the mentioned models and to compose an artificial sediment for the laboratory experiments. In the following the progress of the three project parts of GASSTAB is described.

Numerical Modeling McIver's model shows a large block of cemented sediment, breaking off and sliding downslope on a layer of liquefied sediment (Fig. 1a).

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Figure 1: (a) above, Model after McIver, (b) below, Transfer of Fig.1a into a soil mechanical model.

The results of stability calculations are shown in the picture below. Fig. 2a shows the factor of stability (η = Qmax / Qin situ ) versus the slope angle (α) and the inclination of destabilized gas hydrate layer (β). The stability of the slope is documented by η >1, left to the thick line

describing the critical state. Fig. 2b shows the variation of the critical state line for different friction angles (the thick line is the same as in Fig. 2a). The gray shaded area corresponds with the in situ observed slope and sliding plane angles. Similar relations were found by varying the cohesion and the length of the sliding plane, respectively.

Figure 2: (a) above, Slope stability versus inclinations, (b) below, Nomogram of critical state lines for different friction angles.

A verification of the analytical results is in progress using numerical simulations with finite elements on different platforms. Furthermore dynamical tests are planed to include the triggering phase of the failure mechanism.

Soil Mechanical Material Behavior The strength of sediments in natural deposits is mainly controlled by the stress history which they have undergone as well as by the actual stress and pressure regime within their grain skeleton and their void. Stress history of marine sediments which follow hydrate formation and decomposition has neither been experimentally nor theoretically investigated so far.

GASSTAB will make a first contribution both experimentally and theoretically to understand and quantify stress history and current stress and pressure states of sediment, gas and hydrate systems.

For experimental investigation of these complex interrelations a special Gas Hydrate Test System is under construction. GTS will be an oedometer type device. It will enable the formation and decomposition of gas hydrates under real deep sea conditions and simultaneously allow the measurement of stress â&#x20AC;&#x201C; strain reaction within the sediment. Controlled boundary conditions are: sediment volume and stresses, pore water pressure, gas pressure, temperature and spatial distribution of gas hydrate.

For the detailed design and the construction of GTS a set of preliminary tests were inevitably necessary. Physicochemically preliminary tests for the formation of gas hydrates were performed with tetrahydrofurane (THF) and propane. Additionally equipment for high pressure tests with methane has just been just completed. The observed effect of the waterâ&#x20AC;&#x2122;s metastable cluster states on the kinetics of gas hydrate formation led to a redesign of the peripheral pressure devices of the GTS. Further preliminary tests were conducted in order to find a suitable method to measure the spatial distribution of hydrates within the sample chamber. Ultrasonic propagation, electrical resistance and temperature were measured. As a result electrical resistance measurements were selected for deployment in GTS. In co-operation with Kiel University of Applied Sciences an electrical resistance tomography will be developed, to detect the spatial distribution of the gas hydrates in the sediment.

Preliminary soil mechanical tests are in progress, to synchronize optimize the design and dimensioning of the electrical sensor technology and to develop GTSâ&#x20AC;&#x2122;s controlling

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algorithms. For this purpose an oedometric device was re-equipped. First tests with THF hydrates in sands have been started.

The theoretical approach is based on a numeric modelling of the mechanical sediment - gas hydrate interaction. With the aid of DEM (Distinct Element Method) a virtual testing tool is being developed to simulate gas hydrate formation and decomposition. This provides the advantage to run virtual tests under various boundary conditions considerably faster than real tests.

First trials have been carried out to simulate the growth of hydrate crystals in the pore space of sediments.

Actual Petrographic Sediment Conditions The assessment of gas hydrate containing sediments requires knowledge of the sedimentological, petrographical and soil mechanical index properties. As for the experiments with GTS larger amounts of sediment are required, an artificial sediment had to be created. The following two main questions had to be answered: are there special properties allowing hydrate to grow and what will the artificial sedimentâ&#x20AC;&#x2122;s composition be? For this purpose 96 sediment samples from ODP leg 164 were investigated. The samples, from zones above, within and below gas hydrate containing layers were studied (by SEM analysis) with regard to their grain size distribution, clay mineral composition and microtexture. The values of certain additional parameters like water content, bulk density and shear strength had to be gained from literature, as significant changes to the original state of the samples had taken place.

The sediments can be generally classified as silty clays or clayey silts with little variation in their sand contents. In most of the samples taken from one and the same sediment layer the grain size changed significantly. So the sediment is homogeneous on the large scale (> 10 cm) but highly variable on the small scale. No grain size differences between sediments above, within and below gas hydrate containing layers could be found.

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SEM investigations of 35 different sediment samples have shown that they are mainly composed of flaky shaped, small sized clay minerals, calcareous nannofossils, foraminifers, diatoms and small amounts of grains. The number of open pores within the sediment stabilized by biogenitic shells decreases with depth below the sediment surface. Sediments from the gas hydrate bearing zones did not show more open pores than layers without hydrates.

X-ray investigations of 10 samples (fraction < 2 Âľm) from different sediment depths (50 m 700 m) have shown that within the whole section illite (50 wt%) is the dominating mineral followed by kaolinite (40 wt%) and chlorite (10 wt%).

Because we cannot be sure that the sediment samples we investigated ever contained gas hydrates, different artificial sediments, taking into account the determined small scale variability, have been composed. Clay minerals from a Kulm clay stone and a kaoline deposit were mixed with varying amounts of pure biogenetic components for the coarser fraction.

These artificial sediments will be used for all future GASSTAB soil mechanical tests. On the other hand this variation of the composition has the advantage of investigating the effects of grain size, clay mineral content and different biogenetic components on gas hydrate formation.

Literature McIver, R. D. , Role of naturally occurring gas hydrates in sediment transport. American Association of Petroleum Geologists Bulletin, 66, 789-792, 1982 Proceedings of the Ocean Drilling Program, Vol. 164, Scientific Results, 2000 Proceedings of the Ocean Drilling Program, Vol. 164, Initial Reports, 1996

An in-situ laboratory array for biogeochemical processes under deep sea conditions with and without fluid venting Gubsch S., Viergutz T., Gust G., M端ller V., Holscher B. Ocean Engineering 1, Technical University Hamburg-Harburg, 22305 Hamburg, Germany

Investigations of temporal and spatial variability of composition and decomposition processes of natural gas hydrates require undisturbed environmental conditions. In-situ experiments where gas hydrates remain embedded in their original sedimentary matrix provide adequate conditions for such undisturbed experiments and permit to investigate physical, chemical and biogeochemical mechanisms related to composition and decomposition of surfacenear gas hydrates. Within this project (LOTUS, TP 1) an in-situ laboratory array for biogeochemical processes under deep sea conditions with and without fluid venting has been developed and successfully tested .

Main components of the laboratory array are two benthic and one fluid-column laboratories: the Fluid Flux Observatory, the Biogeochemical Observatory and the Particle Flux (Carbon Flow) Observatory. These Observatories work either independently or synchronously to complement each other in their research tasks.

correlation between tidal signal and fluid flow from or into the sediment and represented an important first step towards the identification of dynamical processes associated with gas hydrate stability. Subsequently executed laboratory experiments revealed additional influences on the measurement by lateral flow and the permeability of the sediment.

Advances beyond currently used measuring systems required to consider these effects.

Further desirable steps for improvements were determination of the direction of the fluid flow (in- or outflow) and the quantification of the ratio between vented gas and water. To meet these goals, our group developed a completely new flow measurement system and, in addition, established a laboratory calibration facility for FLUFO systems under simultaneous exposure to horizontal and vertical flow.

Major objective of the Fluid Flux Observatory (FLUFO) is to identify and quantify the effective discharge rates related to composition and decomposition of gas hydrates and to discern the impact of environmental parameters such as temperature, pressure, permeability and near bottom currents.

The new designed measurement system - reduces the effects from lateral flow by selection of a suitable geometry - reduces the effects from lateral flow by preventing leakage out of the device - quantifies the ratio gas/water in the venting fluid - quantifies the permeability of the sediment - determines the direction of vertical flow (in or out) - increases the sensitivity and dynamic range of discharged flow volume

Fluid flow released from sediments containing gas hydrates were found already during the 90ies (e.g. Carson et al., 1990 / Linke et al., 1999) from long term deployments of vent barrels. These measurements indicated a

These advancements are linked to a new basic procedure for the measurement of fluid discharge based on a tracer method.

An integral part of the development of the new flow measurement system were extensive

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numerical simulation for hydrodynamic performance of the fluid-flux-measuring system.

Especially the pressure dependence of the interaction between the measuring system and the fluid out- or inflow to the bottom was investigated as a decision criterion for the selection of an optimised performance to measure very slow flow velocities in an open system. For assessing the influence of changed boundary conditions between calibration and deployment of the system, either the laboratory or typical in-situ boundary conditions are taken into account. A data reduction code exist which will be used to evaluate measured data of the Ortega I cruise.

With the Biogeochemical Observatory (BIGO), the temporal variability of the biologically facilitated turnover in the sediment and fluxes across the sediment water interface are studied at time scales ranging from days to weeks. For realising adequate hydrodynamic conditions inside the chamber the flow velocity is measured by a sensor and transmitted to a calibrated stirring device which generates and maintains equal hydrodynamic conditions. The time series of chamber bottom stress can alternatively be artificially maintained, continuously adjusted to changes of environmental flow parameters, or freely programmed by a preselected look-up table. With this laboratory, chemical and biological in-situ experiments are executed independently of vertical fluid release.

The hydrodynamic conditions at the confined sediment-water interface are realised by a twoparameter control of the stirring device. Its outstanding feature is a spatially homogeneous bottom stress with steady or variable time history inside the chamber. The features of this patented chamber have been improved further by providing - an energetically optimised version of the in situ stirring-and-pump system, - optimised experimental space inside the chamber by changing the geometry of the stirrer while maintaining spatially homogeneous bottom stress. This change resulted

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in experimentally accessible sediment surface from the chamber lid of more than 500 cm2.

The main features of the hydrodynamic performance of both systems FLUFO and BIGO were successfully tested both in laboratory experiments and under real conditions during the cruise ALKOR 192 at water depths of 329 and 315 meter. Biogeochemical processes at the sediment-water interface are not only affected by the hydrodynamic conditions but by the presence of particulate matter as well. Sources are either sinking particles from surface and pelagic regions, or resuspended particles advected with the flow. The Particle Flux Observatory (PAFLO) provides a means to quantify this mass flux and associated carbon/ nutrient flux. It is intended to quantify with this observatory the extent to which biomats observed to thrive at methane release areas are dependent on either or all of the stimuli of interfacial hydrodynamics, the release of constituents from the venting fluid and the settling of particulate matter from above and upstream.

This project utilises a new patented trapping protocol for particulate matter in connection with PAFLO where the in-situ sinking-particle flux is obtained from the collection rates of cylinders of different geometries which form a multiplett of simultaneously deployed traps.

The mass collected in these traps follow independent accumulation equations per trap type (developed in another research project) and are used to establish an equation system which is solved for the concentration of sinking particle sub groups involved. Multiplied with the sinking velocities the fluxes of these particle sub groups are obtained (Gust and Kozerski, 2000).

The three observatories have been developed and tested to a level that the scientific missions to be met during research cruise Ortega 1 in hydrate-bearing sediment zones can be approached with novel, advanced and tested gear.

Details of the design features, equations and

array performance in the Baltic and the Atlantic are presented.

References Carson B., Suess E., Strasser J.C. (1990) Fluid Flow and Mass Flux Determinations at Vent Sites on the Cascadia Margin Accretionary Prism. J. Geophys. Res. 95/B6: 8891-8897.

Gust, G. and Kozerski, H.P.: In-situ sinking-particle fluxes from collection rates of cylindrical traps. Marine Ecology Progress Series, 208 (2000), pp. 93 â&#x20AC;&#x201C; 106.

Linke, P., O. Pfannkuche, M. E. Torres, R. Collier, U. Witte, J. McManus, D. E. Hammond, K. M. Brown, M. D. Tryon, K. Nakamura: Variability of benthic flux and discharge rates at vent sites determined by in situ instruments. Eos. Trans.

AGU, 80(46), 1999, Fall Meet. Suppl., F509.

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Gas hydrate dynamics – Modelling hydrate formation in near surface sediments Haeckel M., Suess E., Wallmann K., Rickert D. GEOMAR Research Center for Marine Geosciences, Wischhofstraße 1-3, 24148 Kiel, Germany

Massive gas hydrate layers are formed in the near-surface sediments of the Cascadia margin. A nearly undissociated piece of hydrate could be recovered at the base of a gravity corer (i.e. in 120 cm sediment depth) on the southern summit of Hydrate Ridge. As a result of salt exclusion during the methane hydrate formation, the associated pore waters show a highly elevated chloride concentration of 809 mM, compared to the normal values of 18 543 mM. Corresponding δ O and δD profiles indicate that the chloride anomaly certainly originates from hydrate formation.

From this first field observation of a positive – Cl anomaly, we calculate comparatively high hydrate formation rates (0.5-1.2 mol cm –2 a –1) [1], also revealing a highly dynamic system.

Our simple non-steady state diffusion-advection model also constrains the rate of fluid flow at the Cascadia accretionary margin to be 110-250 cm a –1 [1]. These rates are orders of magnitude higher than rates previously reported for deep-seated sedimentary hydrates (Blake Ridge, ODP site 997) [2].

Furthermore, the calculated flux of methane from below that is needed to build up the necessary amount of methane hydrate which causes the observed chloride enrichment strongly suggests that most of the gas hydrate must have been formed from ascending methane gas bubbles rather than solely from CH4 dissolved in the pore water.

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References [1] M. Haeckel, E. Suess, K. Wallmann and D. Rickert, Rising methane gas-bubbles form massive hydrate layers at the seafloor, Geology, submitted.

[2] P.K. Egeberg, G.R. Dickens (1999), Thermodynamic and pore water halogen constraints on gas hydrate distribution at ODP Site 997 (Blake Ridge), Chemical Geology 153, 53-79.

Temperature profiles during a gas hydrate production test Henninges, J., Schrötter J., Erbas K., Huenges E., and the Mallik working group GeoForschungsZentrum Potsdam, AB 5, Telegrafenberg, 14473 Potsdam, Germany

Currently the extraction of gaseous methane from natural gas hydrates is discussed as a potential future source of energy. The stability of gas hydrates mainly depends on the physical variables of state pressure and temperature. Both the size and the distribution of natural gas hydrate deposits, as well as the release of gaseous methane through the dissociation of gas hydrates, is influenced by the underground pressure and temperature conditions.

During the field experiment (Fig. 1), which was carried out in the framework of the Mallik 2002 Research Well Program from December 2001 to March 2002 in the Mackenzie Delta in northwestern Canada, the spatial and temporal variation of temperature during a gas hydrate production test was measured. During the production test the dissociation of gas hydrate was stimulated by circulating hot fluid in a segment of the borehole within the target horizon. The temperature throughout the depth of the central production well and two lateral observation wells was recorded with distributed temperature sensors (DTS).

Through the deployment of the DTS technology continuous temperature profiles (distance of data points < 1 m) along the boreholes can be determined with high temporal resolution (measurement interval > 7 sec). Temperature is calculated from the reflected signal of a laser pulse transmitted through a optical fibre cable.

The temperature data can be registered online through a opto-electronic surface readout unit.

Prior to the field experiment the DTS system was calibrated in a temperature controlled chamber at the GFZ Potsdam. With the

calibrated DTS apparatus an accuracy of the measured temperature data of 0,2 °C can be achieved.

The temperature profiles at the Mallik site show characteristic features in the relatively thick permafrost layer (approx. 0m – 600m) and the gas hydrate zone (approx. 900m – 1100m). Figure 2 shows a temperature profile for the Mallik 3L-38 observation well 63 days after completion. The base of the ice-bonded permafrost is marked by a distinct change of the temperature gradient. Especially in the permafrost section the temperatures may locally still be under influences resulting from the drilling and completion of the well. As a result of the lower bulk thermal conductivity, the gas hydrate zone shows higher temperature gradients as compared to the hydrate-free sediments above and below.

Figure 3 shows a schematic diagram of the downhole test configuration and temperature profiles in the thermal stimulation zone of the production well. The temperature profiles show the increase in temperature for successive points in times from before the test to the maximum temperature conditions. The distribution of temperature along the wellbore exhibits a characteristic pattern which results from the heat exchange between the well and the surrounding formation and the inflow of gas and fluid through the perforated section of the borehole casing.

The first review of the collected field data already shows, that DTS temperature monitoring is a powerful tool for the observation of temperature related processes in boreholes.

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With the presented online temperature monitoring system a previously unachieved resolution in space and time could be achieved. The high quality of the collected temperature data proves the applicability of the system, even under extreme arctic conditions. Through the installation of the sensor cables in the cement annulus outside the casing of the borehole, a permanent deployment without interference with other installations in the borehole was made possible. In combination with other geophysical and geological data, the method is well suited for many different reservoir engineering applications.

Figure 1: Schematic cross section of the setup for the field experiment. The optical fibre cables are attached to the outside of the borehole casing and embedded in the cement annulus after completion of the well.

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Figure 2: Temperature Profile for the Mallik 3L-38 observation well 63 days after completion of the well. The profile is characterized by the ice-bonded permafrost layer (approx.

0m to 600m) and the gas hydrate zone (approx. 900m to 1100m) which display different temperature gradients.

Figure 3: Schematic diagram of downhole test configuration and temperature profiles in the thermal stimulation zone. The temperature profiles are displayed for 3h, 20h and 35h after the start of circulation.

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Pyrite Crusts from the Black Sea: Mineralogy and Genesis Hübner A., Halbach P. Freie Universität Berlin, FR Geochemie, Hydrogeologie & Mineralogie, Malteserstr. 74-100, Haus B, 12249 Berlin, Germany

Introduction Pyrite is found abundantly in the uppermost sediments (Unit I and II) of the Black Sea, in contrast to lesser amounts of pyrite in Unit III. It is uniformly dispersed as fine-grained, mainly framboidal grains (Unit I and II) or anhedral grains (Unit III). Pyrite (or principal reactants: mackinawite and intermediate reduced S species) in Unit I and II is believed to form within the anoxic water column and within the sediment (Muramoto et al., 1991). Sedimentary pyrite formation is limited mainly by iron availability in the most recent (Unit I) nonturbiditic sediments. Berner (1974) recognized older sediments (in Unit III) that are black and rich in iron monosulfides (metastable precursors of pyrite), whereas the younger sediments were grey and rich in pyrite rather than in iron monosulfides. An upward increase in salinity and consequent availability of sulfate was suggested to cause the observed succession.

In contrast to the above described abundance of dispersed pyrite in sediments, massive pyrite crusts are a very rare occurrence in the Black Sea, in fact they have been sampled only once, and limited studies were undertaken to elucidate their origin (Lein et al., 1995; Peckmann et al., 2001). Here, we contribute new data on the texture of pyrite, presenting collomorph textures being a formerly overlooked, but principal feature of the pyrite within the crusts. Stable isotope distributions of S in the pyrite comprise a narrow range of surprisingly positive values close to seawater sulfate-S isotope distributions. A genetic model is presented to account for the above and previously published results on these unusual sulfide precipitates.

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Material and Methods The samples were obtained from the Ukrainian slope in the north-western Black Sea using a beam trawl, which was deployed in water depths between 178 – 198 m. The pyrite crusts occur as individual pieces containing only negligible amounts of carbonate, and the carbonate crusts in turn are devoid of pyrite.

They have a diameter of up to 15 cm, are firm, dark grey and covered partly with a thin (<1mm), light carbonate. Some pieces show secondary native S efflorescence. The form of the crusts is irregular, some are massive and others show hollows and irregular tubes, resembling fluid pathways as found in high-temperature sulfide chimneys from ocean ridges.

Results Mineralogy: XRD-analysis of the pyrite crusts revealed that their constituents are almost exclusively pyrite and quartz. Measured S-contents of different pieces of crust were between 21.4-37.7 wt.%, resulting in pyrite contents of 40-70 wt.%, assuming all S is present in pyrite.

Table 1: S-Isotope distribution of different crust samples

sample SMP-A01 SMP-B01 SMP-C01 SMP-D01

δ34S (‰) 9,46 17,78 18,73 15,06

sample SMP-E01 SMP-F01 SMP-G01

δ34S (‰) 18,40 17,83 14,25

Polished sections: From 6 individual crust samples polished sections were prepared and investigated under light und scanning electron microscope. The following textures of pyrite were distinguished: (a) individual angular grains of about 1µm in diameter which are not connected to each other.

(b) spherical aggregates (framboids: diameter: 5-40 µm) made up of individual pyrite crystals (microcrysts) of 1-3µm. Frequently, the latter show different degrees of amalgamation which fill the remaining spaces in between and induce the formation of massive pyrite spherules. (c) framboids that are surrounded by a rim of massive pyrite. The thickness of the rim varies from thin, being considerably less than the radius of the framboid, to very thick. The rim often shows radial textures.

This enclosing rim may be developed further to the next type of pyrite observed in the crusts: (d) massive, colloform pyrite (melnikovite) with remnants of framboids. This massive pyrite often features cauliflower-like banding textures around single or groups of framboidal pyrite crystals.

Discussion Seep carbonates precipitate on the sea floor of the Black Sea around methane gas seeps as a result of increased alkalinity due to bacterially mediated anoxic methane oxidation. Another product of this reaction is dissolved reduced S, which may react with Fe 2+ to form pyrite. One surprising result of the GHOSTDABS-cruise with R/V “Professor Logachev” in July 2001 in the Black Sea was the complete absence of pyrite from seep carbonates, which were extensively sampled from the sea floor.

Additionally, the pyrite crusts which were sampled in an area where seep carbonates do occur, are free of carbonates, apart from a thin carbonate cover on some parts of the crusts.

This leads us to the hypothesis that different sites of mineral precipitation for these phases must exist.

Figure 1: Examples for pyrite morphologies in pyrite crust samples from the Black Sea: from left to right, according to text above (a) individual microcrystals, (b) framboids, (c) framboids with rim and (d) colloform pyrite with framboid relics. Scale bars are 5µm for type (a) and 20 µm for types (b) to (d). Types (a) to (c) photos

by SEM, (d) photo by light microscope .

Figure 2: Genetic model of pyrite crust precipitation. For explanation see text .

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The exact formation pathway of sedimentary pyrite is still debated, but consensus exists that pyrite does form mainly via precursor minerals in the following succession: Fe2+ + S2- ¢ disordered mackinawite (FeS) ¢ ordered mackinawite ¢ greigite (Fe3S4) ¢ pyrite (FeS2) The synthesis of Fe-monosulfides may be written according to Rickard et al. (1995): Fe2+ + S2- ¢ FeS + 2H+ In this reaction, protons are produced, which are considered to play a key role in lowering the pH of the system and therefore inhibit carbonate precipitation at the site of Fe-sulfide mineralisation. In our model, the above reaction takes place within the sedimentary column along the pathways of upwards-migrating methane, where S 2 – is produced continuously by anaerobic methane oxidation/sulfate reduction. The HCO3–, which is also a product of anaerobic methane oxidation, is carried further upwards. With contact of the Black Sea bottom waters, carbonates precipitate and may eventually form chimney-like structures (Fig. 2).

Microorganism activity is assumed to be very strong along the pathways of migrating methane. Additionally, the supply of dissolved suphate to the reaction site is restricted by the diffusion from the seafloor surface.

For these reasons, sulfate-limited conditions may develop along and in the vicinity of the seep pathways, leading to nearly-closedsystem conditions in the S-system. This scenario would cause a _34S signature in pyrite similar to that of marine sulfate.

The formation of the conspicuous framboidal texture of pyrite is thought to occur after the conversion of mackinawite microcrystals to greigite, and is attributed to the strong ferromagnetic property of greigite which attracts single microcrystals to spheric aggregates. Contrasting this, colloform pyrite is produced when the rate of crystal nucleation is

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greater than the growth rate, implying very fast reaction of dissolved iron and dissolved reduced S-species. Further work will be done to elucidate the formation histories of these two distinctively different textural occurrences of pyrite in the crusts from the Black Sea. References Berner R. A. (1974) Iron sulfides in Pleistocene deep Black Sea sediments and their paleo-oceanographic significance. In The Black Sea Geology, Chemistry and Biology, (ed. E. T. Degens and D. A. Ross), pp. 524-531.

American Association of Petroleum Geologists Memoir, 20.

Lein A. Y., Egorov V. N., Pimenov N. V., Gulin M. B., Luth C., Artyomov Y. G., Polikarpov G. G., Thiel H., and Ivanov M. V. (1995) Sulfide chimneys in the Black Sea (in Russian). Doklady Rossiiskoi Akademii Nauk. 310, 676-680.

Muramoto J. A., Honjo S., Fry B., Hay B. J., Howarth R. W., and Cisne J. L. (1991) Sulfur, iron and organic carbon fluxes in the Black Sea: sulfur isotopic evidence for origin of sulfur fluxes. Deep-Sea Research 38 (Suppl.), S1151S1187.

Peckmann J., Reimer A., Luth U., Luth C., Hansen B. T., Heinicke C., Hoefs J., and Reitner J. (2001) Methane-derived carbonates and authigenic pyrite from the northwestern Black Sea. Marine Geology 177, 129-150.

Rickard D. T., Schoonen M. A. A., and Luther G. W. (1995) Chemistry of iron sulfides in sedimentary environments. In Geochemical Transformations of Sedimentary Sulfur (ed. M. A. Vairavamurthy and M. A. A. Schoonen), pp.

168-193. American Chemical Society.

Structure and dynamics of gas hydrates: Recent results Itoh H., Goreschnik E., Klapproth A., Kuhs W.F. GZG Abt. Kristallographie, Universität Göttingen, Goldschmidtstr. 1, 37077 Göttingen, Germany

Gas hydrates have an ice like structure yet have many distinct physical properties from ice such as glass-like thermal conductivity (Andersson and Ross, 1983; Tse and White, 1988). In spite of recent investigations, however, there are still many remaining unresolved problems relating to the microstructure and dynamic properties of gas hydrates. Molecular dynamics (MD) simulations are powerful tools to investigate the microstructure and dynamic properties of gas hydrates. A suitable water potential model used in MD simulations is a key to correctly predict their properties precisely. In order to establish a good interaction model for water in a gas hydrate system, it turns out that a crucial test is the ability to reproduce the low frequency modes of gas hydrates. Low frequency dynamic properties of gas hydrates have been studied using Raman (Nakahara et al., 1988), IR (Klug and Whalley, 1973), and neutron spectroscopy (Tse et al., 1993; Tse et al., 2001; Gutt et al., 2002). From inelastic neutron scattering (INS) experiments we are able to obtain the precise low frequency data and compare with MD simulation results.

However, for methane hydrate, it is difficult to distinguish the lattice modes from CH4 modes because of high incoherent scattering cross section of CH4 (321.0 barn) compared with D2O (4.1 barn). In this study we therefore have done INS experiments of Ar-, Xe-, O2 - and N2hydrates with deuterated samples using a time focusing time-of-flight spectrometer. In addition to the INS experiments, we have demonstrated an accuracy of water potential model used in the present MD simulations by the assignment of low frequency modes in doubly occupied N2-hydrates.

Inelastic neutron scattering experiments were

performed using the time-of-flight spectrometer IN6 at the Institut Laue-Langevin (ILL) with various gas hydrate samples which were independently prepared from powdered ice Ih. To distinguish vibrations of guest molecules from those of water molecules it is necessary to employ the sample of deuterated gas hydrates.

The material synthesis was performed by exposing powdered ice to well-defined gas pressures at well-defined temperatures for two weeks: D2O (Ar, O2 and N2: 180 bar, Xe: 10 bar, N2: 2 kbar) at 273 K and H2O (N2: 180 bar) at 271 K. Details of the sample preparation can be found in the literatures (Kuhs et al., 1997; Staykova et al., 2002).

Molecular dynamics calculations of N2-hydrate have been performed using the Kumagai, Kawamura and Yokokawa (KKY) potential model (Kumagai et al., 1994) which allows unconstrained atomic motions. The parameters for water were optimized so as to revise the dielectric constant of liquid water. As a result the lattice vibrational frequencies of hexagonal ice Ih are in good agreement compared with our old model (Itoh et al., 1996).

The parameters for nitrogen were fitted to reproduce the potential curvature for N2- N2 with four different configurations. The model used in the present MD calculations contains 1088 H2O for a structure II clathrate hydrate with cubic Fd3m cell dimensions a = b = c = 34.40 Å (2 x 2 x 2 unit cells). We put 128 N2 molecules in small cages and 64 N2 molecules (singly occupied) and 80 N2 molecules (doubly occupied) in large cages. Both constant volume (N, V, T) and constant pressure (N, P, T) MD calculations were performed for 40 ps (100,000 steps) with a time step of 0.4 fs.

The power spectrum, which related to the

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vibrational density of states (VDOS), is simply the Fourier transform of the atom velocity autocorrelation function. More details of calculations are described in our previous paper (Itoh et al., 2001).

We have measured Ar-, Xe-, O2 - and N2hydrates. Here we present one of our important results that Xe- and N2-hydrate have different spectral features. Figure 1 shows the generalized susceptibility χ’’(ω) of Xe- and N2hydrate in the low-frequency region as a function of temperature. In the Xe-hydrate case (Fig. 1(a)) only the first peak at about 2 meV shows a slight anomalous softening, while the peak at 2.9 and 4.0 meV does not have temperature dependency. The Xe-peak at 2.3 meV (above 100 K) softens slightly with decreasing temperature to 2.1 meV at 60 K. This is in agreement with the predictions from MD simulations (Inoue et al. 1996) with a peak at 2.5 meV at 260 K shifted to 2.1 meV at 100K as well as with the experimental results on the hydrogenated system by Tse et al. (2001) and Gutt et al. (2002). Moreover, the peak frequencies of the Xe-modes obtained in our experiment are in good agreement with the results of MD simulations (Tse et al., 1983; Inoue et al., 1996).

In contrast to Xe-hydrate, the first low frequency peak at about 2 meV in N2-hydrate has very strong temperature dependence. As can be seen from Fig. 1(b), the maximum position of the peak in the generalized susceptibility χ’’(ω, Q) softens from about 2.2 meV to 0.8 meV with the temperature decreasing from 160 K to 20 K. The softening is accompanied by a strong increase in intensity. The calculated spectrum of N2 molecules in large cages at 18.6 cm-1 (2.30 meV) is in good agreement with this peak observed experimentally. The N2-mode in large cages has more anharmonic vibration than the Xe-mode in large cages (see Fig. 1(a)). In the frequency range over 5 meV we have observed a two peak structure centered at 7 and 10 meV. This spectral feature is distinct from the spectrum of hexagonal ice (which shows only one well-

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defined peak at about 6.2 meV) and provides a fingerprint of the open cage structure of the host lattice. While the peaks are centered approximately at the same frequencies as those in Ar- and Xe-hydrates, the first peak has a strongly enhanced intensity. The enhancement at 7 meV can be assigned to N2 external vibrations in small cages corresponding to the peak centered at about 60 cm-1 (7.4 meV) calculated by MD simulations at 180 bar (see Fig. 2). It is dominated by a strong band centered at about 7 meV, i.e. exactly at the position of the first peak of the host lattice. This assignment is also supported by the N2-contributions to the spectrum of N2-hydrate which are calculated from the difference between N2hydrate and Ar-hydrate.

Inelastic neutron scattering experiments on different types of gas hydrates have been performed. In addition we have demonstrated an accuracy of interaction model for water and nitrogen molecules by the assignment of low frequency modes in N2-hydrate. We found that the spectral features of two intense peaks at about 7 and 10 meV are distinct from the spectrum of hexagonal ice and provide a fingerprint of the open cage structure of the host lattice. From a comparison of the experimental N2-contributions to the spectrum and the results of MD simulations we can clearly assigned N2 internal modes in small and large cages. From our INS experiments and MD simulations, we conclude that not only each gas hydrate has a different spectral feature for its guest modes but also exhibits a variable coupling of the guest modes with the host lattice. For instance, comparing the low frequency modes in large cages, Xe-modes are less anharmonic than N2-modes. In addition MD simulations using the KKY potential model used in this study well reproduced the dynamic properties of gas hydrates. It is important to note here that this variation in anharmonicity may well affect relevant physical properties like thermal conductivities. In this light, generalized statements on the respective physical behavior of gas hydrates seem problematic. Rather it appears that for each hydrate and each gas

mixture the relationship between structure and dynamics and its physical properties must be established on a individual basis before we can attempt a more generalized view.

Figure 1: Generalized susceptibility χ’’(ω) of Xe-hydrate (a) and N2-hydrate (b) in the low-frequency region as a function of temperature. Note the difference in anharmonic shift with temperature especially for the lowest energy mode.

Figure 2: N atom power spectra for small and large cages at 80 K and at 180 bar as obtained from a 40 ps MD run.

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References Andersson, P., & Ross, R. G. (1983). Journal of Physics C: Solid State Physics 16, 1423-1432.

Gutt, C., Baumert, J., Press, W., Tse, J. S., & Janssen, S. (2002). Journal of Chemical Physics 116, 3795-3799.

Inoue, R., Tanaka, H., & Nakanishi, K. (1996).

Journal of Chemical Physics 104, 9569-9577.

Itoh, H., Kawamura, K., Hondoh, H., & Mae, S. (1996). Journal of Chemical Physics 106, 24082413.

Itoh, H., Tse, J. S., & Kawamura, K. (2001).

Journal of Chemical Physics 115, 9414-9420.

Klug D. D., & Whalley, E. (1973). Canadian Journal of Chemistry 51, 4062-4071.

Kuhs, W. F., Chazallon, B., Radaelli, P. G., & Pauer, F. (1997). Journal of Inclusion.

Phenomena and Molecular recognition in Chemistry 29, 65-77.

Kumagai, N., Kawamura, K., & Yokokawa, T. (1994). Molecular Simulation 12, 177-186.

Nakahara, J., Shigesato, Y., Higashi, A., Hondoh T., & Langway, Jr., C. C. (1988).

Philosophical Magazine B 57, 421-430.

Staykova, D. K., Goreshink, E., Salamatin, A. N., & Kuhs, W. F. (2002). Proceedings of the 4th International Conference on Gas Hydrates, Yokohama, Japan.

Tse, J. S., Klein, M. L., & McDonald, I. R. (1983). Journal of Chemical Physics 87, 20962097.

Tse, J. S., & White, M. A. (1988). Journal of Physical Chemistry 92, 5006-5011.

Tse, J.S., Powell, B. M., Sears, V. F., & Handa, Y. P. (1993). Chemical Physics Letters 215, 383387.

Tse, J.S., Shpakov, V. P., Belosludov, V. R., Trouw, F., Handa, Y. P., & Press, W. (2001).

Europhysics Letters 54, 354-360.

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Geochemical relicts of gas hydrate dissociation in sediments of pockmark sites of the Congo Fan (CONGO) Kasten, S. (1), Hensen, C. (2), Schneider, R. (1), Spieß V. (1) (1) Universität Bremen, Fachbereich Geowissenschaften, Postfach 33 04 40, 28334 Bremen, Germany (2) GEOMAR Forschungszentrum für Marine Geowissenschaften, Wischhofstraße 1-3, 24148 Kiel, Germany

Detailed sampling of pockmarks has been carried out on the Northern Congo Fan during Meteor cruise M47/3 in June/July 2000. Four gravity cores were retrieved that covered or reached almost the depth of complete sulfate depletion – i.e. the zone of anaerobic oxidation of methane (AOM).

In this contribution we focus on two pockmark sites where the zone of anaerobic oxidation of methane was reached at different sediment depths (Fig. 1). At the flank of one of the pockmarks (site GeoB 6520) gas hydrates were found below 5 m sediment depth. Pore water data revealed a flux of methane from the hydrate-bearing zone into a sulfate/methane transition located at about 2.2 m sediment depth. A second pockmark site (GeoB 6521) revealed numerous authigenic carbonates distributed over the whole sediment depth of 11.5 m. The zone of anaerobic oxidation of methane at this site is located at a depth of 11 m below the sediment surface characterized by a very narrow zone (app. 1 m) where the gradient of sulfate shows a conspicuous steepening.

Although the gas hydrates found at site GeoB 6520 are stable with respect to temperature (3°C) and pressure (3100 m water depth) we suggest that they will undergo successive dissolution due to the methane concentration gradient established between the hydratebearing zone below and the zone of AOM. Within the hydrate-bearing sediment interval interstitial methane is in thermodynamic equilibrium with gas hydrates (e.g., Zatsepina

& Buffett, 1997). The consumption of methane by anaerobic oxidation produces a flux of methane from the hydrate zone into the sulfate/methane transition. As a consequence methane is continuously released from the gas hydrates resulting in their successive dissociation irrespective of favorable pressure and temperature conditions.

We assume that at site GeoB 6521 - where no hydrates were found in the upper 11.5 m - gas hydrates must have been present there as well and that they are likely to have dissolved according to the process described above. The large amounts of alkalinity produced by the process of anaerobic methane oxidation led to the formation of authigenic carbonates which are almost homogenously distributed over the whole sediment depth covered by this core.

The dominant phase is Mg-calcite (~13% Mg) followed by aragonite with δ13C values ranging between –44 and –60‰ thus suggesting at least partly a biogenic source of methane (Fig. 2). Most of the aragonitic carbonates (associated with increased Sr concentrations) are found in the upper part of GeoB 6521 indicating that they were formed when carbonates precipitation took place under oxic conditions close to the sediment/ water interface (e.g., Walter, 1986).

Further support for a successive downward progression of the zone of anaerobic methane oxidation induced by dissociation of gas hydrates comes from the solid phase distribution of barium. Authigenic barites typically precipitate slightly above the zone of sulfate depletion

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(e.g., Torres et al., 1996). Numerous distinct Ba enrichments found above the present depth of the sulfate/methane transition at 11 m indicate that this geochemical front was located closer to the sediment surface in the past and has successively moved downward (e.g., Dickens, 2001). Increased Ba contents mark depths where the zone of anaerobic methane oxidation was fixed for a significant length of time.

Calculations of the time to produce the total amount of authigenic Ba in the sediment interval above the present depth of the zone of AOM by upward diffusion of Ba 2+ give a minimum time period of about 18500 years assuming an average porosity of 75%.

Our results demonstrate the potential of authigenic minerals formed in the zone of anaerobic methane oxidation to trace changing fluxes of methane from deeper parts of the sediment as well as dynamics of formation and and dissociation of marine gas hydrates.

Figure 2: Plot of δ13C vs. δ18O of bulk authigenic carbonates in cores GeoB 6520 and GeoB 6521.

References Dickens, G.R. (2001) Sulfate profiles and barium fronts in sediment on the Blake Ridge: Present and past methane fluxes through a large gas hydrate reservoir. Geochim.

Cosmochim. Acta, 65, 529-543.

Torres, M.E., Brumsack, H.J., Bohrmann, G. & Emeis, K.C. (1996) Barite fronts in continental margin sediments: A new look at barium mobilization in the zone of sulfate reduction and formation of heavy barites in diagenetic fronts. Chem. Geol., 127, 125-139.

Walter, L.M. (1986) Relative efficiency of carbonate dissolution and precipitation during diagenesis: aprogress report on the role of solution chemistry. In: Gautier, G.L. (Ed.), Roles of organic matter in mineral diagenesis.

Society of Economic Palaeontologists and Mineralogists, Special Publications, 38, 1-12.

Figure 1: Pore water concentration profiles for pockmark sites GeoB 6520 (”Hydrate site”) and GeoB 6521 (”Carbonate site”) on the Northern Congo Fan.

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Zatsepina, O.Y. & Buffett, B.A. (1997) Phase equilibrium of gas hydrate: Implications for the formation of hydrate in the deep sea floor.

Geophys. Res. Lett., 24, 1567-1570.

Geoacoustic mapping of near-surface gashydrates and associated features in the Black Sea using deep-towed, high-resolution sidescan sonar.

Klaucke I., Weinrebe W., Bohrmann G. GEOMAR, Forschungszentrum Kiel, Germany

A newly acquired full-ocean depth, deep-towed sidescan sonar system (DTS-1, Fig. 1) was used for the first time during cruise M52/1 to the Black Sea. The instrument used here allows imaging the backscatter intensity of the seafloor at high resolution. This surface information can further be integrated with very highresolution subbottom information of the uppermost sedimentary layer, therefore allowing volume estimates of sedimentary units at the seafloor. For cruise M52/1 the instrument was intended to map the occurrences of nearsurface gas hydrates and associated features such as carbonate crusts, gas seeps and pockmarks. As these gas hydrate occurrences in the Black Sea are closely related to mudvolcanism, the surface expression of these mudvolcanoes and of mudflows originating from represented another target for the use of the deep-towed sidescan sonar.

Figure 1: The DTS-1 sidescan sonar towfish during deployment in the Black Sea.

The DTS-1 sidescan sonar is a EdgeTech FullSpectrum (FS-DW) dual-frequency, chirp sidescan sonar working with 75 and 410 kHz centre frequencies. The 410 kHz sidescan

sonar emits a pulse of 40 kHz bandwidth and 2.4 ms duration (giving a range resolution of 1.8 cm) and the 75 kHz sidescan sonar provides a choice between two pulses of 7.5 and 2 kHz bandwidth and 14 and 50 ms pulse length, respectively. They provide a maximum resolution of 10 cm. In addition to the sidescan sonar sensors, the DTS-1 contains a 2-16 kHz , chirp subbottom penetrator providing a choice of three different pulses of 20 ms pulse length each: a 2-10 kHz pulse, a 2-12 kHz pulse and a 2-15 kHz pulse giving nominal resolution between 6 and 10 cm. The sidescan sonars and the subbottom penetrator can be run with different trigger modes: internal, external, coupled and gated triggers. Coupled and gated trigger modes also allow to specify trigger delays. The sonar electronics provide four serial ports (RS232) in order to attach up to four additional sensors. One of these ports is used for a Honeywell attitude sensor providing information on heading, roll and pitch.

Finally, there is the possibility of recording data directly in the underwater unit through a massstorage option with a total storage capacity of 30 Gbyte. The sonar electronic is housed in a titanium pressure vessel mounted on a towfish of 2.8m x 0.8m x 0.9m in dimension (Fig. 1).

The towfish houses a second titanium pressure vessel containing the wet-end of the SEND DSC-Link telemetry system. In addition, an OCEANO releaser with separate receiver head that is now compatible with Posidonia 6000 underwater positioning, and a NOVATECH emergency flash and sender are included in the towfish.

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Control operations of the DTS-1 sidescan sonar are carried out using Hydrostar Online, a multibeam bathymetry software developed by ELAC Nautik GmbH and recently adapted to the acquisition of EdgeTech sidescan sonar data.

This software package allows onscreen representation of the data, of the fish’s attitude, and of the ship’s navigation. It also allows setting some principle parameters of the sonar electronics, such a the selected pulse, the range, the power output, the gain and the ping rate. HydroStar Online also allows to start and stop data storage either in XSE-format on the HydroStar Online computer or in Edgetech’s own format in the FS-DW for later upload. Simultaneous storage in both XSE and JSF-formats is also possible.

During cruise M52/1 a total of 530 km2 of lowfrequency (75 kHz) sidescan sonar, 0.4 km2 of high-frequency (410 kHz) sidescan sonar and 410 line km of subbottom profiler data have been collected, despite many initial problems with this new system and new configuration.

Data recovered were of generally good quality and allowed detailed mapping of a number of mudvolcanoes and the extent of mudflows generated by them. Without penetration of the high-frequency sound signal, mudflows

shown on sidescan sonar records are believed to be very young. In this respect, Dvurechenski mudvolcano has shown signs of intense current activity (Fig. 2). At this time it is not yet sure whether these features are related to downslope movements such as mudflows or result from deepsea currents.

Mudflows, however, seem laterally fairly restricted and follow depressions on the flanks of volcanoes. Although subbottom profiler data do not provide information about the age of the deposits, subbottom profiler data from the flanks of mudvolcanoes indicate individual flow channels that are stacked with slight lateral shifts. Mudflow activity is either not continuous or not very voluminous, because

Figure 3: Example of unprocessed DTS-1 subbottom profiler data from the Black Sea showing a number of mudflows.

Please note that the bathymetric profile is not a true profile because of varying altitude of the towfish.

individual mudflows are separated by thin layers of well-stratified sediment of probably hemipelagic origin (Fig. 3). At present it is not clear whether near-surface gas-hydrates have been mapped during cruise M52/1. Processing and interpretation of the sidescan sonar data from cruise M52/1 are still going on and need to be combined with the findings of other groups working on data from this cruise and this area.

Figure 2: Example of unprocessed 410 kHz sidescan sonar data from the flanks of Dvurechenski mudvolcano.

Width of the sonar swath is 100m and 5 min of data (towing speed 3 kn) are shown.

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Molecular Ecology of Anaerobic Oxidation of Methane (BMBF/Geotechnologien project ”MUMM”) Knittel K. (1), Boetius A. (1, 2), Lemke A. (1), Amann R. (1) (1) Max Planck Institute for Marine Microbiology, Bremen, Germany (2) Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Methane is present in huge amounts in marine sediments and exists either as crystalline, solid phase methane hydrates, or as free gas. Little of the methane reaches the oxic water column because it is converted to CO2 by microorganisms in the anoxic sediments. Thus, anaerobic oxidation of methane (AOM) is a globally significant process, since it decreases the flux of the greenhouse gas methane from marine sediments to the atmosphere. There is strong geochemical evidence, based on microbial process measurements and stable carbon isotope data that AOM is directly coupled to sulfate reduction. Recent studies demonstrated that AOM is mediated by a structured consortium of sulfate-reducing bacteria belonging to the Desulfosarcina/ Desulfococcus group and archaea belonging to the ANME-2 group (Boetius et al., 2000; Orphan et al., 2001), which is phylogenetically affiliated with the order Methanosarcinales.

The ANME-2 group is so far known only from 16S rDNA clone libraries; no representatives of it have yet been cultured.

At the Hydrate Ridge off Oregon, discrete methane hydrate layers occur at the seafloor, at a water depth of 600-800 m, associated with intensive venting. The crest of the southern Hydrate Ridge is populated by thick bacterial mats of the sulfur-oxidizing filamentous bacteria Beggiatoa, and by large communities of clams of the genus Calyptogena. Both are indicative of active methane seeping. Undisturbed cores from Beggiatoa mats, Calyptogena fields, and reference stations were obtained during RV SONNE Cruise SO143-2

(August 1999) and SO148-1 (July/ August 2000; Bohrmann et al., 2000).

Integrated over the upper 15 cm, the sulfate reduction rates in the zone of anaerobic oxidation of methane (AOM) are >100 mmol m-2 d-1 and represent some of the highest values ever measured in cold marine sediments. A combination of biomarker studies involving stable isotope analysis and fluorescence in situ hybridization shows that structured consortia of archaea and sulfate reducing bacteria (SRB) are presumably mediating AOM in these sediments (Fig.1A; Boetius et al., 2000). Both archaeal and SRB biomarkers were strongly 13 C-depleted, which is indicative of methaneconsuming microbial communities. The consortia were highly abundant in Hydrate Ridge sediments with a maximum of 1x10 8 aggregates cm-3. The consortia-associated cells accounted for ca. 90% of total cell numbers in these sediments. The diameter of the aggregates ranged from 1µm (aggregates consisting of only 2-4 cells) up to ca. 15 µm, with an average of 3.2 µm (Fig.1B).

The microbial diversity of different sediment layers from Hydrate Ridge (Beggiatoa mat and Calyptogena field) was investigated by 16S rDNA clone library analysis. The bacterial diversity was always high, comparable to that of coastal sediments. The most abundant 16S rDNA sequences were sulfate-reducing bacteria (δ-proteobacteria), γ-proteobacteria and members of the Cytophaga/Flavobacterium cluster. Only very few sequences affiliated with methylotrophic bacteria were retrieved. The archaeal diversity, however, was extremely low.

The sequences belong to recently described

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groups of methanogenic archaea, ANME-1 and ANME-2, and to one group of uncultivated species within the Crenarchaeota.

However, the micro-diversity within these three phylogenetic groups was relatively high, with sequence similarities of 95-100%. The detected bacterial and archaeal diversity is consistent with the results from clone libraries from other methane-rich sites such as the Gulf of Mexico (Lanoil et al., 2001) or the Eel River Basin (Orphan et al., 2001). We are also planning to compare the microbial diversity of Hydrate Ridge sediments with other sampling sites with respect to the methane source.

FISH analysis showed a highly active microbial community in sediments below the Beggiatoa mat and Calyptogena field consisting of about 70% bacteria and 30% archaea (Fig.2). The percentage of archaea increases strongly with depth. However, at the reference station the percentage of archaea is very low, accounting for a maximum of 10% of total DAPI cell counts.

Additional data on the abundance and vertical distribution of different groups of sulfate-reducing bacteria will be presented.

Figure1: A. In situ-hybridization of archaea/Desulfosarcina aggregate with fluorescently labelled rRNA-targeted oligonucleotide probes. The archaea are shown in red and the sulfate-reducing bacteria of the Desulfosarcina/ Desulfococcus group in green (picture taken from Boetius et al., 2000).

B. Size spectrum of DAPI-stained aggregates.

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References Boetius, A., K. Ravenschlag, C. Schubert, D. Rickert, F. Widdel, A. Gieseke, R. Amann, B. B. Jørgensen, U. Witte, and O. Pfannkuche. 2000.

A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature.

407:623-626.

Bohrmann, G., P. Linke, P. Suess, and O. Pfannkuche. 2000. RV SONNE Cruise Report SO 143: TECFLUX-I-1999. GEOMAR Rep. 93.

Lanoil, B. D., R. Sassen, M. T. La Duc, S. T. Sweet, and K. H. Nealson. 2001. Bacteria and Archaea physically associated with Gulf of Mexico Gas Hydrates. Appl. Environ. Microbiol. 67:51435153.

Orphan, V. J., K.-U. Hinrichs, W. Ussler III, C. K. Paull, L. T. Taylor, S. P. Sylva, J. M. Hayes, and E. F. DeLong. 2001. Comparative analysis of methane-oxidizing archaea and sulfate-reducing bacteria in anoxic marine sediments.

Appl. Environ. Microbiol. 67:1922-1934.

Orphan, V. J., C. H. House, K.-U. Hinrichs, K. D. McKeegan, and E. F. DeLong. 2001. Methaneconsuming archaea revealed by directly coupled isotopic and phylogenetic analysis.

Science. 293:484-487.

Figure 2: A. FISH of sediments covered by a Calyptogena field (Station 185, 0-1 cm depth) with a general bacterial probe (EUB338 I-III).

B. DAPI staining (same microscopic field).

MARGASCH – Marine gas hydrates of the Black Sea: First results from a high resolution 3D multichannel seismic survey Krastel S., Spieß V., Zühlsdorff L. Dept. of Geosciences, University of Bremen, P. O. Box 330440, 28334 Bremen, Germany, skrastel@uni-bremen.de

The existence of gas hydrates in marine sediments was first proved in the Black Sea, the largest anoxid basin in the world. Since then, near surface gas hydrates were regularly sampled in marine sediments of the Black Sea. The main objective of the interdisciplinary research cruise of the German R/V Meteor in early 2002 (Project MARGASCH: Marine gas hydrates of the Black Sea) was to study the distribution, structure, and architecture of gas hydrate occurrences in the Black Sea as well as their relationship to fluid migration pathways.

The investigations were concentrated in two areas: the central Black Sea and the Sorokin Trough, southeast of the Crimean peninsula.

Here we will present seismic data from the Sorokin Trough (Fig. 1).

A GI-Gun with 0.4 L chamber volume (100500 Hz) and a Sodera water gun (200-1600 Hz) were used in an alternating mode along all seismic lines. The data were recorded by means of a 600-m-long Syntron streamer (48 channels) equipped with separately programmable hydrophone subgroups. Hydroacoustic systems (Parasound, Hydrosweep) were used simultaneously on each seismic line during the cruise. The seismic survey was divided into two parts. 44 seismic lines were shot as overview profiles to image the principal structures of the survey area. Based on these results we chose a 2.5 km x 7.5 km large box for a three-dimensional survey with a line spacing of 25 m (Fig. 1).

Figure1: Profile plan of the seismic survey in the Sorokin Trough.

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The Sorokin Trough is characterized by diapiric structures and compressional tectonics that facilitate fluid migration to the seafloor.

Abundant mud volcanoes and near surface gas hydrate occurrences were identified in this area. The seismic overview profiles allows to image these features. The diapiric ridges are of particular interest since they are caused by the protrusion of plastic, water-saturated Maikopian clays. The ridges strike in a WSW-NEN direction, which is parallel to the general trend in the Sorokin Trough. Mud volcanoes are found above the diapiric ridges.

A typical example crossing two different types of mud volcanoes is shown on Line GeoB 02003 oriented in a SSW-NNE direction (Fig. 2).

The larger mud volcano at the southwestern end of the profile is the Kazakov mud volcano.

Kazakov mud volcano is cone-shaped with a diameter of ~ 2.5 km and a height of ~ 120 m above the surrounding seafloor. The area beneath Kazakov mud volcano is characterized by a transparent zone with a width similar to the diameter of the mud volcano probably serving as the main feeder channel. This zone can be vertically traced to more than 1.5 s TWT, which is the maximum seismic penetration of our system. Whether Kazakov mud volcano is located on a fault zone is not clearly imaged by the seismic data but reflectors, which could be identified in the upper part of the section, do not show a major offset.

Another type of mud volcanoes is located between CMPs 850 and 1100 on Profile GeoB 02003 (Fig. 2). These volcanoes belong to a belt of mud volcanoes associated with a morphological step. The diameters of the mud volcanoes imaged on Line GeoB 02-003 are ~ 1 km for the mud volcano located around CMP 900 and 500 m for the mud volcano at CMP 1050; the heights are 45 m and 15 m, respectively. The feeder channel in the upper 300 â&#x20AC;&#x201C; 400 ms TWT reveals about the same diameter as the mud volcano itself. Diapirs are clearly imaged beneath. These structures are interpreted as mud diapirs originating from the Maikopian formation, which is characterized by low-

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density clays and plastic behavior. In total, three different types of smaller mud volcanoes located above or on the edges of near surface mud diapirs can be distinguished in the Sorokin Trough: cone-shaped, flat-topped, and collapsed.

Despite the known near-surface occurrences of gas hydrates, bottom simulating reflectors were not present in our seismic lines. The reason for this might be that gas hydrates did not occur as massive gas hydrate layers but are finely dispersed in the sediments. However, pronounced lateral amplitude variations and bright spots may indicate the occurrence of gas hydrates and free gas but more detailed processing and interpretation of the seismic profiles is necessary to identify and quantify gas hydrates and free gas.

Based on the results of the overview profiles a 2.5 km x 7.5 km large box was chosen to collect a three-dimensional seismic data set.

This data set will allow to trace structural features, amplitude variations, and pathways for fluid-flow in three dimensions. All shots of the three-dimensional survey were also recorded with 14 Ocean Bottom Hydrophones/ Seismometers and these data will be used for a seismic tomography. Both data sets will be jointly interpreted.

A lot of questions remain open at this early stage of the project. Key questions are: - What causes the different shapes of the mud volcanoes?

- Are different forms of mud volcanoes bound to particular features in the subsurface?

- What is the relationship between mud volcanoes, gas hydrate occurrences, and free gas?

- How are gas hydrates laterally distributed and is it possible to quantify the gas hydrates?

We hope to answer these questions by a detailed analysis of the seismic and other data collected during the cruise. The data set consisting of geological, geochemical, and geophysical data provide a great opportunity to improve our knowledge on the distribution, structure, and architecture of gas hydrate

occurrences in the Black Sea, and on their relationship to fluid migration pathways.

Figure 2: CMP-Stack of seismic Line GeoB 02-003 crossing Kazakov mud volcano and group of unnamed mud volcanoes. CMP distance is 20 m.

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Microbial methane turnover in different types of marine sediments – The MUMM-Project – Krüger M., Treude T., Nauhaus K., Eppelin A., Boetius A., Widdel F. Max-Planck-Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany

Introduction The abundance of active CH4 seeps, like gas hydrates, mud volcanoes, leaks of gaseous CH4 and organic rich sediments, illustrates the important role of the oceans in the global CH4 cycle. However, in contrast to terrestrial and freshwater habitats, much less is known about the processes and microorganisms involved in the CH4 turnover in marine environments.

Within the MUMM-project we therefore investigate the processes involved in CH4 production and consumption at a number of marine sites (Figure 1), with a special focus on gas hydrate bearing sediments. Samples collected at CH4 seep areas are compared to control sites with normal background CH4 concentrations. Rates of anaerobic (AOM) and aerobic CH4 oxidation together with CH4 production are determined combining radiotracer (on-site) and in-vitro measurements.

Results & Discussion In the present study we demonstrated for the first time net AOM in sediment samples (Hydrate Ridge) under laboratory conditions (Nauhaus et al. 2002). Furthermore, we could show that the stoichiometry of AOM is in accordance with the equation – – CH4 + SO4 2 – ¢ HCO3 + HS + H2O. The comparison of AOM-rates obtained with this new method or using radiolabeled CH4 resulted in similar values (Figure 2). The establishment of a method for the in-vitro determination of AOM and the availability of active sediments allows further detailed studies of the processes and mechanisms of AOM as well as of the microorganisms involved.

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Figure 1: Map with the distribution of important sampling sites for the MUMM-project.

Figure 2: Comparison of rates of anaerobic oxidation of CH4 at two sites, either determined on-site using 14 C-labeled CH4 or in vitro via sulfide production (mean ± SD, n = 3-5).

The rates of AOM in samples from gas hydrate areas and methane seeps are several times higher than in low-methane sediments.

Additionally, aerobic methane oxidation was important at many sites where the sediment was in contact with oxic bottom water. Here, rates of aerobic methane turnover were similar

to those of anaerobic methane oxidation. A first estimation of aerobic and anaerobic oxidation activity showed that methane consumption in low-methane sediments, which are most widespread, is on a global scale quantitatively at least equally important, despite the higher rates (per volume) of methane oxidation in and near seeps. Methane production in organic-rich subsurface sediments was generally high, especially if sulfate as electron donor was limiting. These results support the role of methanogenesis as important methane source in the marine cycle.

Outlook Current and future experiments are focused on (I) detailed CH4 turnover measurements at methane seeps and control sites, (II) the identity of the intermediate(s) shuttled in the consortium and other aspects of AOM physiology, and (III) the isolation and identification of key microorganisms involved in aerobic and anaerobic methane oxidation, and CH4 production.

Methodology Rates of AOM were determined with radiotracers (Boetius et al. (2000), Nature 407, 623626), or using a newly developed in-vitro method via the monitoring of sulfide production (Nauhaus et al. (2002), Environmental Microbiology, in press). For the latter, sulfide production from sulfate is compared in the presence or absence of CH4. Rates of aerobic CH4 oxidation and of CH4 production were determined non-radioactively (Kr端ger et al.

(2001), Global Change Biology 7, 49-61).

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Physico-chemistry and properties of gas hydrates: Preliminary answers to some open questions.

Kuhs W.F., Klapproth A., Itoh H., Goreshnik E. GZG Abt.Kristallographie, Georg-August Universität Göttingen, 37077 Göttingen, Germany

We present a number of open questions related to the physico-chemical properties of natural gas hydrates. The questions concern the microstructure, some theromodynamic aspects as well as the formation and decomposition kinetics of these compounds. We were tackling these questions experimentally employing a number of techniques (diffraction, Raman- and inelastic neutron scattering, electron microscopy and computer simulations).

Physical properties A number of physical properties of natural gas hydrates are still poorly known. The more prominent gaps are thermal conductivity, thermal diffusivity and the acoustic wave velocities. Here we concentrate on the latter. The knowledge of acoustic velocities is of considerable importance to the interpretation of seismic data.

Recent attempts to establish them by adiabatic methods (transducer measurements) proved difficult (Helgerud 2001) as sample compaction is a non-trivial process. We have now for the first time successfully measured the isothermal compressibilities of pure methane hydrate. The results are shown in Fig.1.

Cage filling and stoichiometry Essentially all predictions of the stoichiometry of gas hydrates are based on the statistical thermodynamic theory of van der Waals and Platteeuw (1959). The validity of this theory has not been thoroughly checked so far. Most methods do not allow to determine the absolute filling of both small and large cages. Only diffraction can give definite answers. We now have obtained first results on the filling for small and large cages in the system CH4 •x H2O.

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While the large cages are almost completely filled, the small cages show a significantly lower filling than expected from the statistical thermodynamic theory as shown in Fig.2.

Microstructure and kinetics Gas hydrates were found to exhibit sub-micron porosity (Kuhs et al.2000). The porous microstructure may well influence a number of physical parameters (thermal conductivity, wave speeds) as well as the mechanical and thermal stability of gas hydrates. At present it is still unclear to what extend this sub-micron porosity exists in natural settings. Based on our laboratory experiments the existence of sub-micron porosity seems to be indicative for fairly fast formation processes (on a time scale of days to a few weeks) with excess of gas. In a separate paper (poster 28) we present aspects of the reaction kinetics of porous hydrates together with a mathematical model for the growth (Salamatin & Kuhs 2002, Staykova et al. 2002).

Sub-micron porosity was found in natural gas hydrates in a collaborative effort with GEOMAR on samples from Hydrate Ridge (Suess et al. 2002). By a comparison of samples from our laboratory experiments with natural material from the sea floor we can deduce the conditions of growth of the latter.

Molecular modelling Computer simulations are an important tool to interpret a number of experimental results. The nature of gas-water and water-water interactions on a molecular level is still far from being understood. We have refined existing interaction potentials to fit and interpret neutron scattering results on the dynamics of host-

guest interactions (Chazallon et al. 2002, Itoh et al. 2002) a summary of which is presented in a separate paper (poster 27). With such refined interaction potentials we expect to be able to better predict stability limits as well as the composition of pure and mixed gas hydrates.

References Chazallon, B., Itoh, H., Koza, M, Kuhs, W.F. & Schober, H. (2002) Phys.Chem.Chem.Phys. submitted Helgerud, M.B. (2001) PhD-Thesis, Stanford University.

Itoh, H., Chazallon, B., Schober, H., Kawamura, K. & Kuhs, W.F. (2002) Proceedings of ICGH2002.

Kuhs, W.F., Techmer, K., Klapproth, A., Gotthardt, F. & Heinrichs, T. (2000) GRL 27, 2929-2932.

Figure 1: Lattice constants of deuterated and hydrogenated methane hydrate vs. gas pressure. The slope gives the bulk modulus which is different for both materials. The hydrogenated system delivers a value of 9.11 GPa, the deuterated system a value of 8.21GPa. These isothermal values can be transformed into adiabatic values using standard thermodynamic relations to give 9.9 GPa and 8.9 GPa for the hydrogenated and deuterated system respectively.

Salamatin, A.N. & Kuhs, W.F. (2002). Proceedings of ICGH-2002.

Staykova, D.K., Hansen,T., Salamatin, A.N., Kuhs, W.F. (2002) Proceedings of ICGH-2002.

Suess, E., Bohrmann,G.,Rickert, D., Kuhs, W.F., Torres, M.E., Trehu, A. & Linke, P. (2002).

Proceedings of ICGH-2002.

Van der Waals, J.H. & Platteeuw, J.C. (1959) Adv.Chem.Phys. 2, 1-57.

Figure 2: The filling of the small cage in a type I methane hydrate structure at T=271K as a function of methane fugacity.

The data cannot be fitted satisfactorily with a Langmuirisotherm. Langmuir-isotherms taken from literature predict distinctly higher fillings incompatible with our data.

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Experimental methods for the laboratory investigation of gas hydrate containing sediments Kulenkampff J. (1), Spangenberg E. (1), Naumann R. (2) (1) Department of Petrophysics and Geothermics, GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany, hannes@gfz-potsdam.de, erik@gfz-potsdam.de (2) Department of Material Properties and Transport Processes, GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany, rudolf@gfz-potsdam.de

Introduction Estimations of the natural methane hydrate resources vary over at least one order, which is partly due to questionable interpretations of geophysical parameters. The petrophysical data base on which such interpretations are based is very weak and the conditions for methane hydrate generations, stability, and decomposition are not well understood.

This is the reason for the initiative at the GFZ to investigate physical properties of natural methane hydrate and the hydrate formation process in the laboratory under well-characterized conditions. The aim of the laboratory investigations is to develop empirical relations and theoretical models for the formation of gas hydrates in sediments and for their physical properties.

Field laboratory for the investigation of natural gas hydrates A Field Laboratory Experimental Core Analysis System (FLECAS) for the determination of physical properties of gas hydrate containing sediments was developed and successfully applied at the Mallik research well. The advantage of such a field system is that there is no need for transport and storage over a long period, so that the sample alteration can be minimized.

The experiments yield data sets for the electrical resistivity, ultrasonic p- and s-wave velocities and absorptions, as well as the hydrate content, porosity, and permeability of the samples. Because the experiment starts at

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deep frozen condition it also models the condition of gas hydrates in the permafrost zone.

The setup consists of a pressure vessel with an internal heat exchanger for cooling the sample below the freezing temperature. Methods to prepare the samples at low temperature without thermal stress have been developed.

The sample is inserted into the vessel at deep frozen conditions, when the hydrates are practically stable. The confining pressure (simulating the in situ lithostatic pressure, typically 20 MPa at 900 m) and a pore pressure with nitrogen gas (simulating the hydrostatic fluid pressure, 10 MPa at 900 m) are applied. Then the sample is heated to the in situ temperature, holding confining and pore pressure constant.

During the whole procedure electrical resistivity (with a 6 electrode setup) and ultrasonic p- and s-wave velocities are monitored and the end point yields the geophysical properties under in situ conditions.

After reaching the in situ temperature the hydrate decomposition is initiated with a pore pressure drop, releasing the N2 gas and the free pore water. At this moment, both the ultrasonic attenuation and velocity decrease strongly, while the resistivity increases due to the loss of pore water. The dissociation starts immediately, which is obvious from the sudden temperature decrease of the sample. Then the methane gas builds up a pore pressure, and the resistivity decreases again, which is due to the released hydrate water. At last the gas is released through a flow meter for volume determination and stored for chemical analy-

sis. Then the hydrate water is pushed out with a N2 - flow through the sample. The hydrate content can be determined from the hydrate water content and the methane volume.

Synthetic gas hydrate containing sediments Another laboratory gas hydrate experimental apparatus is set up to simulate the conditions under which gas hydrate forms in the sea floor sediments and in the permafrost regions (pressure range: 0-20 MPa; theoretical temperature range of the apparatus: (-5 â&#x20AC;&#x201C; 40 °C).

This apparatus allows measuring seismic velocity, electrical resistivity, and thermal conductivity under in situ conditions. It consists of a 2chamber insulation box. The first chamber of the insulation box is kept on a temperature above the stability field of the hydrate and contains the pressure vessel where the water is charged with methane. The water with the solved methane is pumped into the measuring cell in the second chamber of the insulation box, which is kept on a temperature within the hydrate stability field. Hydrate forms within the artificial sediments in the cell from water and solved methane. The physical properties of the sediments can be measured. The process of hydrate formation out of a solution of water and methane is a very slow process. The first experiments have shown, that the determination of the amount of hydrate formed in the sediment from the pressure drop in the system is difficult because the pressure drop from normal leakage is higher than that from hydrate formation. To overcome this problem we developed an inline high-pressure conductivity cell to calculate the amount of hydrate from the increase in conductivity. The conductivity of the pore water increases during hydrate formation because salt is not build into the hydrate structures and the salinity of the remaining pore water increases with increasing amount of formed hydrate.

microscope and a long distance 80x objective was used. Spectra were collected with a Peltier-cooled CCD detector. The 488 nm line of an Ar ion laser and a power of 400 mW was used for sample excitation. Spectra were obtained from different grains. The spectrum fromeach spot was averaged over 5 accumulations. The signal was integrated 20 s for each accumulation. All investigated methane hydrate samples are sI-hydrates.

Figure 1: Measurement result with FLECAS: 1) relative resistivity change, compressional wave velocity (uncalibrated) and relative amplitude 2) injected oil volume and sample length 3) pore pressure and confining pressure (20MPa) 4) temperature (v1,v2: vessel; s1,s2: sample).

X-ray diffraction applied with a freezing stage is used for the identification of hydrate phases and determination of the ice-hydrate proportions and lattice constants.

Structural investigation The mineralogical structure of the synthesized samples is investigated with Laser Raman spectroscopy and powder X-ray diffraction. A Dilor XY Laser Raman Triple 800 mm spectrometer equipped with an Olympus optical

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Status of development of long-term observatories for gas hydrate research within the collaborative project LOTUS Linke P. (1), Pfannkuche O. (1), Gust G. (2), Sommer S. (1), Gubsch S. (2), Poser M. (3), Greinert J. (1) (1) GEOMAR Forschungszentrum für Marine Geowissenschaften, Kiel, Germany (2) Meerestechnik 1, Technische Universität Hamburg-Harburg, Germany (3) Oktopus GmbH, Hohenwestedt/Kiel, Germany

The overall objective of LOTUS is to monitor in situ the complex trigger mechanisms of formation and destabilisation of gas hydrates on different time and space scales and thus contribute to improved mass balances and diagenetic and prognostic modelling. This will be realised by deploying novel video-guided, long-term observatories for the sediment water interface (SP 1) and the water column (SP 2), by dating and interpretation of the natural geo-archives (SP 3) as well as by process-oriented modelling of the benthic processes (SP 4).

Within subproject 1 of LOTUS, the temporal variability of physico-chemical and biogeochemical mechanisms during decomposition and formation of gas hydrates will be studied using two novel benthic observatories. Measurements will be performed on time scales which are long enough to record the range of naturally occurring control factors. This is in contrast to former short-term measurements which were conducted only in the range of hours (biologically mediated processes) to weeks (fluid flux measurements).

The Fluid-Flux-Observatory is applied to the complex physico-chemical controlling mechanisms of decomposition and formation of gas hydrates, inducing different forms of fluid fluxes (efflux, stagnation, influx), at time scales of weeks to several months. Changes of temperature, pressure, micro-seismicity, near bottom currents (induced e.g. by tides), the release and buoyancy of gas bubbles and related complex

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processes in a two-phase flow system are monitored.

The Biogeochemical Observatory collects data on the temporal variability of the biologically mediated methane turnover at the sediment water interface within lander-integrated mesocosms over time scales of days to 1 week.

Inside the mesocosms the abiotic ambient environment (e.g. oxygen content, flow regime) is actively maintained and continuously adjusted to changes of these parameters (intelligent system). Using an experimental approach the coupling between the benthic methane turnover and changes of environmental conditions (e.g. oxygen content, flow regime, and flux of organic carbon) is simulated inside these mesocosms.

Within subproject 2, the fate of methane in the water column is elucidated with a variety of novel observatories. As free gas is regarded as an important methane source, a sonar-like swath system “Gas-Quant” was developed in cooperation with L3-communications ELACNautik. Integrated into a lander system, it is used for long-term quantification of gas plumes emanating from the seafloor. Improved METS methane-sensors (CAPSUM) are deployed in distinct water layers within a mooring to determine the dissolved methane content over extended time periods. Finally, the impact on these plumes by the complex hydrodynamic regime within and beyond the gas hydrate stability field is monitored with a long-ranging ADCP mounted to another lander.

Distribution of Methanotrophic Microbial Communities at the Haakon Mosby Mud Volcano (MUMM project) Lösekann T. (1), Nadalig T. (2), Knittel K. (1), Boetius A. (1, 2), Sauter E. (2), Schlüter M. (2), Klages M. (2), Amann R. (1) (1) Max Planck Institute for Marine Mikrobiology, Bremen, Germany (2) Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Microorganisms living in anoxic marine sediments are consuming more than 80% of the methane produced in the world’s oceans. Thus, anaerobic oxidation of methane (AOM) is a globally significant process, since it decreases the flux of the greenhouse gas methane from marine sediments to the atmosphere. AOM is thought to be mediated by a structured consortium consisting of methanogens and sulfate-reducing bacteria.

The most important focussed sources of methane in marine environments are gas hydrates, methane seeps and mud volcanoes.

Mud volcanoes are located at all continental margins where large gas deposits are located beneath the seafloor. While first results are available on AOM at gas hydrates and methane seeps, little is known about the microorganisms mediating AOM at mud volcanoes.

We investigated the Haakon Mosby Mud Volcano (HMMV, Barents Sea) as one geological model system representative. The HMMV is located on the continental slope north-west of Norway at a water depth of 1250 m. Its diameter is about 2 km, with an outer rim populated by methane-depending, chemosynthetic communities and an inner center of about 500 m in diameter where fresh mud is expelled. The microbial community structure and diversity in sediments from three different sampling sites were investigated by fluorescence in situ hybridization (FISH). Additionally, 16S rDNA clone libraries for bacteria and archaea were constructed. More than 400 clones were screened by amplified ribosomal DNA restriction analysis (ARDRA) and phylogenetically analyzed.

The composition of the microbial community varied significantly across different HMMV sites and depended on the methane concentrations in the sediment. In contrast to other methanerich environments the bacterial diversity was relatively low. The most abundant clone groups belonged to methylotrophic bacteria (Methylomonas sp., Methylophaga sp.), Cytophaga sp. and some groups of sulfatereducing bacteria. Archaeal sequences were found and could be affiliated to the archaeal groups ANME-1 and ANME-2.

FISH experiments showed that the microbial community in sediments from below a mat of giant sulfide-oxidizing bacteria in the southern part of the HMMV is dominated by archaea. In contrast to gas hydrate sites (e.g. Hydrate Ridge), mostly non-structured aggregates were found in high numbers (up to 2x107 /cm3 ). Only few aggregates occurred in direct physical association with bacteria. More frequently monospecies aggregates of archaea were found, which could be affiliated to the ANME2 group (Fig. 1). This archaeal group belongs to the order Methanosarcinales and is known to be capable of AOM (Boetius et al., 2000; Orphan et al., 2001).

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Figure 1: Fluorescence in situ hybridization of non-structured ANME-2 archaeal aggregates a) = left, Epifluorescence micrograph of HMMV aggregates stained with DAPI b) = right, Epifluorescence micrograph of HMMV aggregates hybridized with probe EelMS932.

Only few structured aggregates were found and these looked very similar to the consortia detected in Hydrate Ridge and Eel River Basin Sediments (Boetius et al., 2000; Orphan et al., 2001). In contrast to these already described aggregates, the bacterial partner in HMMV aggregates could not be affiliated to a known group of sulfate-reducers and still needs to be analyzed phylogenetically.

In the central barren area of the HMMV methane seeps directly from the sediments to the hydrosphere. At this site consortia abundance is several orders of magnitude lower than at the Beggiatoa site. The low abundance of consortia correlated with the methane seeps indicates that methaneoxidizing microorganisms could represent an efficient biofilter reducing the methane emission to the watercolumn.

Additional data on consortia abundance, vertical and spatial distribution will be shown.

References Orphan et al. (2001): Methane-Consuming Archaea Revealed by Directly Coupled Isotopic and Phylogenetic Analysis. Science 293 Boetius et al. (2000): A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407

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Mallik 2002: The Mallik Data and Information System LÜwner R. (1), Conze R. (1), Wächter J. (1), Krysiak F. (2), Laframboise R. (3), and the Mallik working group (1) GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany (2) smartcube GmbH, Wermuthweg 7, D-12353 Berlin, Germany (3) Geological Survey of Canada, Terrain Sciences Division, Ottawa, Ontario K1A 0E8, Canada

During the drilling period of the main well hole (Mallik5L-38) we were able to elaborate an information system very close in time and space to the activities and operations at the Mallik drill site and in the laboratories of the Inuvik Research Center.

The first approach of the data management for the Mallik drilling project was the set up of a database structure using the Drilling Information System (DIS). The DIS is an electronical toolbox developed for scientific ICDP drilling projects. It includes a well-tested data model which covers the major entities of the drilling phase, such as drilling engineering, the documentation and archiving of core runs and samples, initial lithological descriptions, borehole measurements, and monitoring data.

This system encompasses various components helping in administration and operation of the system as well as in presentation of the data.

All data are stored in the backend database management system Microsoft SQL Server 2000 which is covered by a Microsoft Access 2000 user interface.

The database management system was implemented on a server at the Inuvik Research Center. The data entered into the system were directly saved on this central server.

The underlying data model had to be adapted several times according to particular requirements and problems of the hydrate research well. Instead of a highly differentiated internal network infrastructure, we chose a simpler model, including the DIS server itself, one client and the core scanner server (see figure 1).

The second main pillar of our work in Inuvik was the core scanner, which was also connected to the system, and which provided

high resolution images which also were stored in the database. Each of the 210 liners of frozen and unfrozen cores, which came to Inuvik could be photographed in a slabbed mode. The expected problems concerning the extreme conditions of temperature caused no big difficulties.

Finally, an important aspect of the project was to inform the participating scientists about the progress of the drilling during the active operational phase. Each day during the project's period, we used to send updated information containing drilling reports and data from the coring phase to the Mallik Web site within the ICDP Information Network. All digital core pictures and archiving information of the core runs were put to our confidential Web sites, under extremely high security.

After the fieldwork of the Mallik project, which was our first involvement in the highly sensitive Gas Hydrate Research, we have gathered a lot of experience and we can underline the success of the data management up to the present.

References Conze, R., Wächter, J. (1998): The ICDP Information Network (http://www.icdp-online.de). - (poster and on-line presentation), AGU Fall Meeting, December 6-10, 1998, San Francisco, California, USA. Conze, R., Krysiak, F. (1999): ICDP On-Site Drilling Information System. - Demo CD including an exemplary data set of HSDP2 drilling, GFZ Potsdam, Germany.

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Figure 1: Internal Network Structure used at the Inuvik Research Center.

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Acoustical studies in the water column in vicinity of Cold Vents and Mudvolcanoes Lom-Keil H. von (1), Spieß V. (1), Krastel S. (1), Greinert J. (2), Artemov Y. (3) (1) University of Bremen, Germany, hvlom@uni-bremen.de (2) GEOMAR Research Center for marine Geosciences, Germany (3) CIME Center for International Marine Explorations, Ukraine

Gas hydrates today are known to occur all over the world and to constitute large reservoirs in permafrost soils and marine sediments. Research activities in this topic therefore gained a lot of attraction in the last years.

In the Black Sea, which is the largest anoxic basin in the world, methane hydrates were already discovered in 1974. Since then, regularly sampling of the marine sediments there showed frequent occurrence of near surface gas hydrates. Furthermore, the venting of gas bubbles in the water column could be detected with appropriate echosounding systems as well as directly observed with video systems. The existence of such gas plumes can usually be related to near surface gas hydrates in the sediments.

During cruise Meteor M52/1 in January 2002, a multitude of acoustic systems was used to study the occurrence, structure and distribution of gas hydrates in the Black Sea. One of the goals in this project was, to try to detect the venting of gas hydrate bubbles in the water column with the shipboard narrow-beam echosounding system Parasound ‘on the fly’ during normal profile operation. However, to detect gas bubbles in the water as a scatter source for acoustical waves, the wave length of the sound signal and the size of the bubbles should be of similar dimension. As the main Parasound signal frequency is only 4 kHz, efforts have been untertaken in Subproject 2 of the LOTUS project to adapt the digital recording system ParaDigMA) to record also the 18 kHz-signal of the Parasound system. In a first attempt, this was achieved by installing a secondary recording

system specifically redesigned for the 18 kHz signal. This is still a comparably low frequency to detect bubbles of mm to cm size, but damping of the signal energy in the water column makes bubble detection in greater water depth difficult for ultra high frequency echosounders.

First model results showed, that the 18 kHz frequency is nevertheless suitable to detect gas bubbles down to 2 – 3 mm in size, if the signal to noise ratios are sufficient. Studies in an area located in water depths of 100 to 800 m in a region, where the venting of gas bubbles is well known, then confirmed with no doubt, that bubbles can be recognized with the 18 kHzsignal of Parasound. This allows to analyze the linkage between the venting of gas and the structure of the underlying sediments directly, because both signals, the one penetrating the seafloor and the one detecting the bubbles are emitted and recorded in parallel (Fig. 1).

Henceforth the newly designed Parasound recording systems will prove as a valuable tool in locating and studying the escape processes of gas hydrates at the seafloor and in the water column.

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Figure 1: Parasound section recorded at a water depth of 500 m. Top: 4 kHz parametric signal showing true topography and internal sediment structure down to a penetration depth of 30 mbsf. Bottom: parallel recorded 18 kHz signal. The echogram delay is shifted vertically to eliminate seafloor topography. Bubble vent sites can be clearly identified as scatter sources in the water column.

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A first estimate of the volume of methane gas associated with gas hydrate occurrence in the Dnieper Canyon area, northwestern Black Sea Lüdmann T., Wong H.K., Konerding P. Hamburg University, Institute of Biogeochemistry and Marine Chemistry, Bundesstr. 55, 20146 Hamburg, Germany

Within the framework of subproject 2 of the GHOSTDABS project “Gas Hydrates: Occurrence, Stability, Transformation, Dynamics, and Biology in the Black Sea”, a reflection seismic study was carried out in the northwestern Black Sea west of the Crimean Peninsula. 1100 km of high-resolution seismic lines were obtained with an 8-channel mini-streamer having an active length of 100 m. A mini-GI gun triggered in the harmonic mode with a total chamber volume of 0.98 l and a frequency spectrum extending from ca. 20 to 300 Hz served as the seismic source. The seismic tracks cross the continental margin from the outer shelf (water depth ca. 80 m) to the deep basin near the location of the MSU Mud Volcano (ca. 2100 m).

The goals of this subproject are: (1) to map the gas hydrate-cemented horizons on the northwestern continental margin of the Black Sea using reflection seismic techniques; (2) to estimate the distribution and possible volume of gas hydrates within the sediments in combination with seismic refraction results obtain by the research group of Prof. Dr. Flüh (GEOMAR, subproject 5); (3) to find appropriate locations to study gas and fluid venting, mud volcanoes as well as gas hydrate outcrops at the seafloor; (4) to evaluate the local tectonic regime in order to improve the prediction of the stability of the gas hydrate deposits; and (5) to characterise the depo-environment by a seismo-stratigraphic interpretation of the reflection seismic data collected as well as by their correlation with the sedimentary facies deduced from selected cores obtained by the research group of Prof. Dr. Reitner (University of Göttingen, subproject 3).

Reflection seismics is an important tool for the detection of gas hydrate accumulations within the sedimentary column. These accumulations are typically accompanied by a bottom simulating reflector (BSR) which marks the base of the gas hydrate stability zone. The BSR has a phase polarity opposite to that of the seafloor reflection, indicating a high impedance contrast between the high p-wave velocity, gas hydratecemented sediments and underlying lower velocity sediments that contain free gas. While gas hydrates within the bottom sediments were already discovered in 1974 by Russian scientists, we were the first to recognize the existence of a BSR in the Black Sea (within the framework of GHOSTDABS).

Our reflection seismic data demonstrate that the BSR is confined to a limited region of the study area (Fig. 1). It occurs within a water depth range of ca. 700 to 1500 m west of the Dnieper Canyon and its maximum depth below the seafloor is ca. 440 m. Below a water depth of 1500 m, the BSR disappears. To compute the depth of the BSR, we used an average p-wave velocity of 1700 km/s for the sediment column down to the BSR depth as determined by a preliminary analysis of one seismic refraction profile of subproject 5. Using the pressure-temperature stability conditions at the base of the gas hydrate zone, the temperature at the BSR depth was estimated.

This, together with the seafloor temperature, yields an average computed thermal gradient of 30 °C/km. This value is in good agreement with published heat flow measurements using a heat flow probe as well as drillhole measurements at DSDP sites (Leg 42B) in the central Black Sea.

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To estimate the possible volume of methane associated with the gas hydrate in the hydrate stability zone and the amount of free gas below it within the study area, we mapped the spatial distribution of gas hydrates using the BSR and assumed an average thickness of the gas hydrate layer as well as the average amount of free gas beneath 1 m3 of gas hydrate published for areas elsewhere. The order of magnitude of this volume is 10 2 km3.

Figure 1: Map showing the depth distribution in mbsf of the BSR (average p-wave velocity: 1700 km/s). Dotted lines indicate seismic tracks where the BSR could be observed. Inset shows the location of the study area.

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Biogeochemical turn over in methane rich sediments at Hydrate Ridge, Cascadia Margin: Quantification using a model approach Luff R., Wallmann K. GEOMAR Research Center for Marine Geosciences, Wischhofstrasse 1-3 D-24148 Kiel, Germany; rluff@geomar.de

At Hydrate Ridge, a part of the Cascadia convergent margin, active venting of fluids and gases from the seafloor (SUESS et al., 2001) and abundant aggregates of bacteria in the sediment (BOETIUS et al., 2000) and bacteria mats on the sediment (SUESS et al., 2001) has been documented. Moreover a large biogeochemical dataset is avaiable from this location. This site is therefore a good example to study the processes in such an extreme environment with a numerical model to qualify and quantify them.

Due to chemical interactions in the upper part of the sediments, only a very small portion of this methane reaches the ocean waters. This is caused by anaerobic methane oxidation in the sediment e.g. (BARNES and GOLDBERG, 1976), (MARTENS and BERNER, 1977), which consumes most of the upwardly diffusing methane, before it can escape the sediments and contribute to water column and finally to the atmosphere (CICERONE and OREMLAND, 1988).The methane from below will be oxidized in this reaction (Formula 1) by a highly specialized archaeal-bacterial consortium (BOETIUS et al., 2000). The reaction occurs in a sharp limited zone near the sediment surface because sulfate from the overlaying seawater, that conduces as electron acceptor for the methane oxidation is present here. A result of this anaerobic reaction is the release of the byproducts sulfid and bicarbonate into the pore water with the consequence of high concentrations of them there.

(1)

The sulfid released from this reaction escapes from the sediment and represents the basis of nutrition for benthic sulfid oxidizing bacteria at the sediment surface, using oxygen and nitrate as electron acceptors. The massive amount of bicarbonate released during the methane oxidation will increase the total alkalinity and supports the precipitation of massive autigenic carbonate/aragonite layers (Formula 2) in the upper sediment centimetres, that has been described by (BOHRMANN et al., 1998).

(2) The numerical early diagenetic model C. CANDI (LUFF et al., 2000) has been used to simulate the biogeochemical processes in the sediments at Cascadia margin to describe the complex system in these specific sediments.

Therefore the model, that originally based on CANDI by (BOUDREAU, 1996) has been enhanced to ensure a realistic description of the thermodynamic processes in this environment. Based on the new method to calculate the thermodynamically controlled acid/base equilibrium and using the individual transport of the species CO2, HCO 3– , CO3 2 – HS – and H2S (LUFF et al., 2001) the model ensures realistic simulation of concentration profiles and therewith fluxes of these species between sediment and bottom water. Moreover the advanced thermodynamic description implemented in the model enables the quantification of carbonate dissolution and precipitation rates, even when sulfid in high concentrations exist.

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Steady state approach Based on the steady state calculations, the carbon budget for this station can be estimated to demonstrate the tremendous turnover in the surface sediment evoked by the advective methane transport from below.

Figure 1 demonstrate the simulated carbon cycle for a cold vent site in general and show the carbon budget at the investigated site at the southern summit of Hydrate Ridge. The picture is divided into a source part on the left and a sink part on the right side. Carbon can reach the sediment at the surface in solid form of particular organic matter (OM) and in form of CaCO3. At the end of the simulated sediment column these species are allowed to leave the area, with the result of a net sink related to the carbon budget. Moreover diffusive and advective fluxes of dissolved carbon species CO2, HCO3-, CO3 2 - and CH4 at the sediment - bottom water interface and also at the end of the sediment column affect the total carbon budget. Espeacilly the advective fluxes of dissolved species from deeper sediment layers represent a huge source of carbon in the surface part of these sediments.

Dissolved organic matter that obviously also exist in nature has been neglected in the model scheme of C. CANDI, all organic matter reach and leave the simulated sediment column in particular form. The general pattern of the carbon budget of the surface sediment at this site, shown in Figure 1 can be pictured out as follows: A strong flux of CH4 from deeper sediments constitute the main source of carbon for the system, while the flux of HCO3– between sediment and bottom water represents the main sink of carbon. The flux of CH4 out of the sediment at the surface is nearly zero. As already mentioned, bacteria in the upper few sediment centimetres will consume the bulk of methane from below. The influx of CH4 and HCO3– from below and the flux out of the sediment at the surface of HCO3 – dominate the complete carbon system at this cold vent site.

The fluxes of the solid species OM that normally force the biogeochemical processes in sediments and CaCO3 do not play a

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significant role in this system (Figure 1). The carbon that reaches this sediment in form of organic matter represents less then 8 percent of the total carbon budget, while the CaCO3 that leaves the sediment at the bottom in form of calcite and aragonite represents about 12 percent.

Non steady state approach The pore water fluxes measured by (TRYON and BROWN, 2001) have been used for a non steady state simulation of this station based on the results of the steady state calculations.

Their in situ fluid flow meter, that measures the flow by determining the degree of dilution of a chemical tracer that is injected in the chamber (TRYON et al., 2001), has been deployed for about 6 weeks on the northern and southern summit. The flow out of the sediment recorded on the southern summit was very high, much higher than typically found on mat sites (Tryon, pers. com.) with maximum values of about 970 cm a– 1. Because of these constrained values we choose the more typically dataset measured on the northern summit for the non steady state forcing of the model. In Figure 2 on top is the forcing for this simulation, interpolated to daily values, shown. To demonstrate the reaction of the sediment to the changes in the fluid flow, the distribution of Ca in the upper 5 cm and SO4 2 – in the upper 3 cm has been choosen. The steady state concentration distributions have been used as starting values for the non steady state simulation. The model time step of this simulation has been chosen to one day.

The moderate increase of the pore water flux during the first 15 days of the simulation is responsible for stronger gradients of the presented concentration distributions in the upper sediment. During this period the depth of the 4 mmol l – 1 isoline decrease of about 1.5 cm and the sulfate penetration depth increase.

The strong increase of the flow up to 240 cm a – 1 between day 15 and 20 forces significantly stronger gradients in the concentrations.

During this period the 4 mmol l – 1 isoline of Ca has been pushed by the flow up to about 1.5 cm sediment depth and the SO42- penetration

depth incerases further on. Weaker fluxes after day 20 from 150 and down to 75 cm a – 1 allow a decrease of the Ca gradients during the rest of the simulation time, while the SO42penetration depth stays relatively constant above 2 cm.

This simulation clearly depicts the strong influence of the pore water velocity to the concentration distributions of the pore water species. Within few days the species concentrations and the gradients in the sediment change significantly only forced by the fluid flow. The strong dependencies between pore

water distributions and fluid flow also can be observed in the concentration profiles Summerizing, the change of the advection velocity has large influence to the concentration distributions of the solute species in the sediment. The concentration profiles of the solid species, espeacilly CaCO3 concentration, that is also directly influenced by the changes in the fluid flow through the concentration of CO32- or alkalinity, are not affected on the simulated short times scales.

Figure 1: Carbonate budget of the first 15 cm of the sediment at this station, presented fluxes are in µmol cm– 2 a – 1 units. The overall carbonate turnover estimated by the steady state approach at this station has been estimated by the model to 1045 µmol cm– 2 a – 1.

Figure 2: Top: Pore water fluxes at the sediment surface [cm a– 1] used as forcing for the non steady state simulation of 44 days to determine the response of the sediment. The fluxes has been measured by (TRYON and BROWN, 2001), the measured values have been interpolated to daily values.

Middle and bottom: Ca and SO42 – concentrations in mmol l– 1 in the upper 5 and 3 cm respectively as a result of the forcing.

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Literature Barnes R. O. and Goldberg E. D. (1976) Methane production and consumption in anoxic marine sediments. Geology 4(297-300).

Boetius A., Ravenschlag K., Schubert C. J., Rickert D., Widdel F., Giesecke A., Amann R., Jorgensen B. B., and Witte U. (2000) A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623626.

Bohrmann G., Greinert J., Suess E., and Torres M. E. (1998) Authigenic carbonates from the Cascadia subduction zone and thier relation to gas hydrate stability. Geology 26(7), 647-650.

Boudreau B. P. (1996) A method-of-lines code for carbon and nutrient diagenesis in aquatic sediments. Computers & Geosciences 22(5), 479-496.

Cicerone R. J. and Oremland R. S. (1988) Biogeochemical aspects of atmospheric methane. Global Biogeochemical Cycles 2, 299-327.

Luff R., Haeckel M., and Wallmann K. (2001) Robust and fast FORTRAN and MATLAB libraries to calculate pH distributions in marine systems.

Computers & Geosciences 27, 157-169.

Luff R., Wallmann K., Grandel S., and Schl端ter M. (2000) Numerical modelling of benthic processes in the deep Arabian Sea. Deep-Sea Research II 47, 3039-3072.

Martens C. S. and Berner R. A. (1977) Interstitial water chemistry of anoxic Long Island Sound sediments. I. Dissolved gases. Limnology and Oceanography 22, 10-25.

Suess E., Torres M. E., Bohrmann G., Collier R. W., Rickert D., Goldfinger C., Linke P., Heuser A., Saling H., Heeschen K., Jung C., Nakamura K., Greinert J., Pfannkuche O., Trehu A., Klinkhammer G. P., Whiticar M. J., Eisenhauer A., Teichert B., and Elvert M. (2001) Sea floor methane hydrates at Hydrate Ridge, Cascadia Margin. Geophysical Monograph 124, 87-98.

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Tryon M., Brown K., Dorman L., and Sauter A. (2001) A new benthic aqueous flux meter for very low to moderate discharge rates. Deep-Sea Research I 48, 2121-2146.

Tryon M. D. and Brown K. M. (2001) Complex flow patterns through Hydrate Ridge and their impact on seep biota. Geophysical Research Letters 28(14), 2863-2866.

Deep microbial ecosystem: biogeochemical characterisation and its potential substrate feedstock (Mallik Research Well 5L-38) Mangelsdorf K., Dieckmann V., Wilkes H., Horsfield B., and the Mallik working group GeoForschungsZentrum Potsdam, PB 4.3, Telegrafenberg, 14473 Potsdam, Germany

For many years conventional wisdom dictated that bacterial processes are restricted to the top tens of metres in sediments, whereas processes in deeper layers and higher temperatures are abiotic (Tissot and Welte, 1984).

Recently, however, microbiologists and geologists have demonstrated that surprisingly large bacterial populations are present at least to hundreds of metres depth, and in this subsurface habitat there is considerable bacterial diversity (Parkes et al., 2000). The discovery of bacteria in both deep marine and deep terrestrial sediments indicates the presence of an ubiquitous and largely unexplored socalled â&#x20AC;&#x153;deep biosphereâ&#x20AC;?. First assessments suggest its biomass to be approximately comparable to that of the Earthâ&#x20AC;&#x2122;s surface, thereby outlining the importance of this widely disseminated hidden world for global geochemical cycles and in this framework especially its role in the formation of gas hydrate deposits and the use of gas hydrates as a potential carbon source.

The Mallik Gas Hydrate Research Well 5L-38, which was drilled in Jan./Feb. 2002 at the northern edge of the Mackenzie River delta (Northern Territories, Canada) provides an exciting and rare opportunity to explore a deep microbial ecosystem in a terrestrial setting near a gas hydrate deposit using organic geochemistry. Our organic geochemical investigations on this subject are addressed to 1) the spatial occurrence and nature of living bacteria in deep ecosystems, and to 2) processes and rates of substrate and nutrient release from the buried organic matter, which can be used as a feedstock for the deep biosphere.

Due to the fact that only a small part of viable microbial communities can be recorded by microbiological methods (Bachofen et al., 1998; Virtue et al., 1996), the use of specific biomarkers, characteristic of those bacterial groups, is an extremely promising tool for identifying and quantifying deep microbial ecosystems. In addition the stable carbon isotopic composition of single biomarkers will be determined to provide crucial information about the carbon source and/or metabolic carbon fixation pathway utilized by its producers. Both sediments and bacterial cultures from the Mallik Gas Hydrate Research Well will come under detailed investigation.

Although it was shown that deep bacterial communities occur in the pore spaces of rocks their carbon/energy sources and the mechanisms of substrate release remain still uncertain. We wish to examine whether small functionalised molecules (carbon dioxide, acetate, methanol etc.) and molecular hydrogen, utilisable by either syntrophs or directly by methanogens, may be generated not only by primary biological processes (as known from near surface environments) but by abiotic reactions in the sub-surface induced by thermal maturation processes. Were this to be the case, deep bacterial activity could become decoupled from the surface biosphere and the biotic primary degradation pathway, its rate being dependent upon the provision of substrate via abiotic chemical transformations and transport processes in the geosphere. To investigate this we will determine the yields of individual generated organic compounds using kinetic and mass balance modelling and

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relating the thermal lability of macromolecular substituents to biological origin using selective degradation followed by kinetic analysis of residues.

Figure 1

Literature Bachofen, R., Ferloni, P., Flynn, I., 1998.

Microorganisms in the subsurface.

Microbiological Research 153, 1-22.

Parkes, R.J., Cragg, B.A., Wellsbury, P., 2000.

Recent studies on bacterial populations and processes in subseafloor sediments: A review.

Hydrogeology Journal 8, 11-28.

Tissot, B., Welte, D.H., 1984. Petroleum formation and occurrence. Springer Verlag, Berlin.

Virtue, P., Nichols, P.D., Boon, P.I., 1996.

Simultaneous estimation of microbial phospholipid fatty acids and diether lipids by capillary gas chromatography. Journal of Microbiological Methods 25, 177-185.

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Acknowledgement We are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support (grant no. MA 2470/1-1).

Structures and processes at methane seeps of the Black Sea Michaelis W., Seifert R., and the shipboard scientific party of the GHOSTDABS cruise Institute of Biogeochemistry and Marine Chemistry , University of Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany

From June 28th to July 22nd the GHOSTDABS– cruise was realized south-west the Crimea peninsula using the Russian RV PROFESSOR LOGACHEV and the German submarine JAGO (Fig. 1). The scientific party comprised participants from the GHOSTDABS project partners (Univ. Hamburg, GEOMAR Kiel, Univ. Göttingen, and FU Berlin), the co-operative projects MUMM (MPI Bremen) and OMEGA (GEOMAR, Kiel), and from international co-operation partners (Moscow, Sevastopol).

At total, 120 stations were carried out during the cruise and allowed to meet the central scientific topics of the GHOSTDABS Project:.

- Localisation and investigation of gas exhalations at the seafloor (vents, seeps, mud volcanoes) and associated structures (carbonates, bacterial mats).

- Inventory of gas hydrate occurrence.

- Gas transfer: gas hydrates – sediment – water column – atmosphere.

- Biogeochemical transformation of gases (methane).

- Microbiological processes related to gas hydrates and methane venting.

Especially the surveys by the submersible JAGO yielded excellent samples and brilliant pictures from the sea floor. Thus we could discover a field of active gas seeps in these anoxic waters at 230 m water depth at a reef of up to 4 m high and 2 m wide structures arising from the sediment (Fig. 2). These structures consist of a cm- to dm-thick microbial mat that is internally stabilized by carbonate precipitates. First results show, that the carbonates, bulk biomass, and particular lipids all incorporate methane carbon as indicated by their strong depletions of 13C. Samples of the microbial

mats could be transferred home alive and are presently object of various detailed investigations performed together with the MUMM project at the MPI in Bremen. They have been found to consist of densely aggregated methanotrophic archaea of the ANME-1 cluster and sulphate reducing bacteria (Desulfosarcina/ Desulfococcus group).

The presence of a Bottom Simulating Reflector (BSR) in the Black sea sediments could be ascertained for the first time by seismic investigation. First estimations of the distribution of gas hydrates and the amount of incorporated methane are realized.

Figure 1

Figure 2

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HDSD – Hydrate Detection and Stability Determination - A Tool For In-Situ Gas Hydrate Destabilisation Mörz T. (1), Brückmann W. (1), Linke P. (1), Türk M. (1), Poser M. (2) (1) GEOMAR Forschungszentrum für Marine Geowissenschaften, Kiel, Germany (2) Oktopus GmbH, Hohenwestedt/Kiel, Germany

Introduction There are two major limitations in the reserve estimations of near-surface gas hydrates: 1) While seismic images, revealing the location of the BSR, and vent phenomena are good indicators for the occurence of shallow gas hydrate thin sediment covers often prevent a direct observation.

2) The limits of the in-situ PT field derived from theoretical models of the hydrate stability field (e.g. Sloan, 1990, Equiphase Hydrate (software

by DBR International Inc., Edmonton, Alberta) differ considerably for a given hydrate deposit and assumed gas composition. Hence the amount of energy needed to mobilize and extract gas from methane hydrate is only approximately known.

To address these limitations a new device is being developed within SFB 574 "Volatiles and Fluids in Subduction Zones". This new tool, HDSD (Hydrate Detection and Stability Determination) will be capable of identifying and quantifying near-surface hydrate layers through local heating and continuous thermal and resistivity profiling. The unit will be highly flexible in its mode of operation due to a fully modular configuration with easily exchangeable components.

Tool and Operation The device is an add-on to the GEOMAR Benthic Chamber Lander, an established and proven technology for video-guided deployment and recovery of benthic experiments. Initial sea trials of the HDSD will be carried out in Summer and Fall of 2002 during RV SONNE and RV METEOR cruises. The initial HDSD configura-

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tion for the first deployment comprises four principal components: A rectangular in-situ experimenting chamber acting as a limiting thermal shield is slowly pushed into the sediment via a motor-driven spindel to a depth of ~30 cm.

An electric heating unit is mounted on the inner upper face of the experimenting chamber which consists of Konstantan coils embedded in an isolating plastic carrier with an aluminum heat exchanger pointing toward the sediment surface. Typical power ratings are 50-100 W. The heating unit can be preprogrammed to generate a constant thermal field. Energy is provided by conventional onboard batteries with a total capacity of up to 1800 W. allowing operation times of 24-36 hours.

A central sensor carrier (sensor lance, 15 mm diameter) is mounted vertically from the chamber top and is equipped with two rows of miniature temperature and resistivity sensors, arranged in a vertical Wenner Array. The sensor arrays provide a fast and closely spaced vertical control of the migrating temperature signal and the resistivity response of hydrate layers within the experimenting chamber.

A data logging and control unit is located above the experimenting chamber and transfers time stamped sensor data to the flash memory of the control unit.

After deployment in its passive state, the sensor array monitors temperature and resistivity profiles and allows detailed insights in the inhomogeneous structural relationship of sediment and interfingering gas hydrate layers of the uppermost 30 cm below the

seafloor. During this stage thermal equilibration after the insertion of the chamber is documented. After the equilibration phase ambient temperature and resistivity profiles are recorded. These profiles will then be used as references to quantify the time-dependent perturbation of the temperature and resistivity profiles during subsequent heating. In its active stage, the heating unit will be used to generate a steep temperature gradient to allow for monitoring and determining the vertical thermal conductivity in various sediment types and settings including hydrate bearing zones.

Optional gas and fluid flow meters are monitoring and quantifying the amount of gas and fluid released during operation.

Status In early 2002 the HDSD heating unit was successfully tested in an 2.5 m 3 laboratory tank filled with water and artificial sand/ bentonite sediment. During 24h experiments sediment temperature at a depth of ~30 cm was raised by 5.5 째C with a steady state temperature gradient of 30 K/m.

Additionally the vacuum mold and a first cast of the sensor lance including all sensors were completed. Currently the data acquisition and control unit is under development.

The tool will be first deployed in July 2002 during RV SONNE cruise 165 (OTEGA) to Cascadia (Hydrate Ridge), were near-surface gas hydrates are occuring in water depths between 600 and 800 m. Theoretical calculations including real gas compositions and salinities indicate that a temperature increase of 6째C should be sufficient to destabilize these hydrate deposits. This well studied area therefore represents ideal test conditions for the new device.

Later on HDSD will be used during SFB 574 to detect hydrates in the associated with mud volcanoes, vents and pockmarks.

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Detailed Seismic Study of a Gas Hydrate Deposit Offshore Costa Rica (DEGAS) Müller C., Bönnemann C., Neben S. Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany

Introduction Gas hydrates are solid substances composed of water and gas molecules, mainly methane, which form under conditions of low temperature and high pressure usually found in the upper few hundred meters of marine sediments in continental margins and in permafrost regions. In the context of energy resources, climate change and seafloor stability, gas hydrates have recently gained increasing scientific and industrial interest. Anyhow, estimates of the global amount of carbon in gas hydrates, about 10 teratonnes following recent estimates (Kvenvolden, 2001), are based on sparse direct observations from drilling. In seismic sections the base of the gas hydrate stability zone is often associated with bottom simulating reflectors (BSRs). In this regard, the enhanced evaluation of remote sensing methods (e.g. seismic techniques) to map and to quantify gas hydrate and free gas content has the potential to improve quantification of local and global amounts of gas associated with gas hydrates.

Survey Area & New Seismic Data BSRs imaged on reflection seismic lines along the Pacific continental margin of Costa Rica are characterized by diverse rather than uniform occurrence. Southwest of Nicoya Peninsula continuous BSRs are observed between water depths of about 600 m on the upper margin and 4000 m at the Middle America Trench (MAT). North of the so called fracture zone trace, in the area of ODP-Leg 170, no BSRs are observed, presumably related to the unusually low heat flow in this area (Kimura et al., 1997). Southeast of Nicoya Peninsula BSRs are characterized by patchy occurrence. In this region, within a 450 km2 3-

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D reflection seismic survey area (Hinz et al., 1992), which is located about 10 km landward of the MAT, BSRs are imaged in an area of about 20 km2. To investigate the patchy occurrence and to quantify the amount of gas hydrate and free gas present in the sediment, eight 2-D high resolution long offset (5250 m) reflection seismic lines have been acquired in 1999 across the 3-D survey area to provide continuous wide angle data (Fig. 1).

Methods & First Results In these post-stack seismic sections BSRs are imaged at about 300 m below seafloor between water depths of about 600 and 3000 m.

Faults are observed at and below BSR depths providing pathways for vertical migration and accumulation of methane-rich fluids. Analysis of the variation of pre-stack reflection amplitude versus angle of incidence (AVA) is implemented to extract acoustic parameters of gas hydrateand free gas-saturated sediments at the BSR. Prominent variations of post-stack and prestack zero-offset reflection amplitudes are observed along the seismic lines, which presumably reflect varying concentrations of gas hydrate and/or free gas. BSR reflections show a clear phase reversal against the seafloor reflection, and source-receiver offsets that are five times the target depth provide incidence angles up to 70°. Due to the lack of any well control in the immediate vicinity of the main study area, high resolution semblance-based velocity analyses constrains AVA modeling. To restore amplitudes at the BSR, source and receiver directivities are explicitly considered.

Amplitude analyses performed at selected points along seismic lines with high S/N ratio BSR reflections show pronounced class III AVA anomalies with strong negative zero-offset

reflection coefficients that increase with offset.

In combination with forward modeling (full Zoeppritz) a differentiation between locations characterized by the solely presence of hydrate and locations characterized by the solely presence of free gas or free gas associated with gas hydrate (Fig. 2) is indicated. Present differentiation is based on the AVA trend at intermediate angles of incidence (~30°-60°), while curves are hardly distinguishable at lower angles and S/N ratio rapidly decreases at far offsets, due to interference at the BSR reflection.

References Kimura, G., Silver, E., Blum, P., et al., 1997, Proc. ODP, Init. Repts., 170: College Station, TX (Ocean Drilling Program).

Kvenvolden, K.A. and Lorenson, T.D., The Global Occurrence of Natural Gas Hydrate, in Natural Gas Hydrates: Occurrence, Distribution, and Detection, edited by C.K. Paull and W.P. Dillon, pp. 3-18, AGU monograph series, 124, 2001.

Hinz, K., and Scientific Crew: Geoscientific investigation off Costa Rica, Pacomar II, Archiv-Nr. 110148, BGR internal report, 1992.

Figure 1: Wide-angle reflection seismic lines are located across the 3-D survey area offshore Costa Rica to determine acoustic properties at the BSR from AVA analyses.

Figure 2: BSR AVA curve extracted from CMP 4500, line BGR99-60, indicates the presence of free gas (reduced Poisson’s ratio model).

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Massive Structures in the anoxic Black Sea: Biomass and carbonate formation based on the anaerobic oxidation of methane Nauhaus K. (1), Treude T. (1), Gieseke A. (1), Knittel K. (1), Boetius A. (1, 2), Michaelis W. (3), Widdel F. (1) (1) Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany (2) Alfred-Wegener-Institute for Polar and marine Research, 27515 Bremerhaven, Germany (3) University of Hamburg, Institute for Biogeochemistry and Marine Chemistry, Bundesstr. 55, 20146 Hamburg, Germany

Active gas seeps occur at water depths between 35 and 800m on the northwestern shelf of the Black Sea, off the Crimean Peninsula.

This methane seepage into the water column makes this an interesting site for the investigation of methane oxidation, especially the anoxic zone (below approx. 130m water depth) where it is most likely anaerobically oxidized. Using the submersible “Jago” from aboard the Russian research vessel “Professor Logachev”, we explored the seafloor of the area. At the depth of about 230 m at 44°46´N, 31°60´S massive structures of biomass and carbonates were discovered above active methane seeps. The almost pure microbial biomass inside of these structures was up to several centimeters thick and in close association with precipitated carbonates. Experiments with radiotracer were performed on board of the ship. Living samples from the mats were incubated under strictly anoxic conditions and taken to the home laboratory to study the molecular identity of the organisms and the physiology of the anaerobic oxidation of methane (AOM).

Carbon isotopic analysis revealed strong depletions of 13C in the bulk biomass as well as in particular lipids (Michaelis, W. personal communication). Therefore the organisms seem to produce their biomass directly from the strongly depleted methane. 13C depletions in the carbonate structures point towards a close coupling of biological activity and carbonate precipitation.

In short-term incubations sulfate reduction and

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methane oxidation were quantified by radiotracer studies. At high methane concentrations these processes apparently take place at a ratio close to 1:1 (Fig. 1). In long-term incubations with mat samples, methane dependent sulfide production from sulfate was demonstrated. This is the second time that the process of AOM could be shown in vitro (Nauhaus et al. 2002). High sulfide production rates (31 µmol d–1 g–1 dry weight) occurred with methane as the only carbon source and electron donor. In controls without methane no sulfide production occurred (Fig. 2). It is believed that AOM is accomplished by two organisms, one of them being a methanogen operating in reverse (oxidizing the methane) and the second one being a sulfate reducer.

Support of this theory so far has come from molecular studies, which showed that most of the biomass in the mats is composed of archaea (ANME-1 cluster) and sulfate reducing bacteria (Desulfosarcina/Desulfococcus group).

Thermodynamic calculations show that the amount of energy gained by this metabolism is quite low (-24 kJ mol –1 CH4) and has even to be shared between the two organisms. Growth rates are therefore expected to be low.

Nevertheless with the use of radiolabeld methane and a beta-Micro-Imager we were able to show carbon incorporation into microbial biomass.

Figure 1: Stoichiometry of sulfate reduction (SR) and anaerobic oxidation of methane (AOM) determined in radiotracer experiments, using two methane concentrations.

Figure 2: Sulfide production with methane as the only electron donor (filled symbols), control without methane (open symbols) over an incubation period of 60 days.

Columns represent sulfate reduction rates (n=6) with and without methane.

Foundations Samples were optained during the Black Sea cruise within the program GHOSTDABS. Laboratory studies were performed within the program MUMM.

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Biomarker evidence of methane oxidation in sediments of Haakon Mosby Mud Volcano Niemann H., Elvert M., Boetius A. Max Planck Institut für Marine Mikrobiologie, Bremen, Celsius Straße 1, 28359 Bremen, hniemann@mpi-bremen.de

Undisturbed sediment cores recovered during cruise Atalante 2001 at the Haakon Mosby Mud Volcano (HMMV) from four different sites (thermal Center, Pogonophora dominated area, Beggiatoa dominated area and a reference station) were for the first time investigated for biomarker signatures and their associated d13C-- values. Preliminary results demonstrate that anaerobic subsurface sediment samples from the biologically active areas are typically enriched in the overall content of bacterial and archaeal lipids directly indicating a high microbial biomass. Moreover, concentrations of specific fatty acids (cis11C16:1), ether lipids (archaeol, hydroxyarchaeol, sn2hydroxyarchaeol), and hydrocarbons (pentamethyicosane (PMI):4, PMI:5) that are commonly found in environments characterized by anaerobic oxidation of methane (AOM) [1, 2, 3, 4] are approximately 3 to 150-fold higher compared to the reference site. Highest lipid concentrations were encountered at one site where sulfur oxidizing Beggiatoa densely cover the sediment. Iincreased concentration of AOM specific biomarkers in the upper most cm compared to deeper layers of the sediment (Fig.1) show that microbial AOM activity is restricted to the subsurface horizon while the deeper layers remain inactive. Small increments may, however, indicate a second “hot spot” of AOM in deeper layers. In contrast, AOM biomarkers were minor in sediments of the thermal center and the Pogonophora dominated site where lipid analysis suggests the dominance of microbial processes other than AOM, most probably aerobic methanotrophy. In the near future, carbon isotope analyses should provide comprehensive evidence of the dominant

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methanotrophic character at the base of the food web at HMMV. Our findings are in very good agreement with direct counts of AOMperforming syntrophic consortia that consists of archaea and sulfate reducing bacteria [5].

References [1] R. D. Pancost, et al., Applied and Environmental Microbiology 66, 1126-1132 (2000).

[2] K.-U. Hinrichs, R. E. Summons, V. Orphan, S. Sylva, J. M. Hayes, Organic Geochemistry 31, 1685-1701 (2000).

[3] M. Elvert, Ph.D. thesis, Christian-AlbrechtsUniversity of Kiel (1999).

[4] M. Elvert, J. Greinert, E. Suess, M. J. Whiticar, in Natural gas hydrates: Occurrence, distribution, and dynamics C. K. Paull, W. P. Dillon, Eds. (American Geophysical Union, Washington DC, 2001), vol. 124, pp. 115-129.

[5] A. Boetius, et al., Nature 407, 623-626 (2000).

a)

b)

Figure 1: (b enlargement of a): Depth profile of AOM specific biomarkers (alcohols: archaeol, sn2hydroxyarchaeol; hydrocarbons: PMI:4, PMI:5; fatty acids: cis11C16:1)in Âľg/gdw at a Beggiatoa site . Increased concentrations indicate high anaerobic oxidation of methane in the subsurface layer.

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Tectonically induced migration of the sulfatemethane-reaction zone in marine sediments of the Sea of Marmara - a case study Reichel Th. (1), Halbach P. (1), Holzbecher E. (2) (1) Free University of Berlin, Dept. for Geochemistry, Hydrogeology, and Mineralogy, 12249 Berlin, Germany. hbrumgeo@zedat.fu-berlin.de, thomasr@zedat.fu-berlin.de, rmoche@zedat.fu-berlin.de (2) Institute of Freshwater Ecology, Department of Eco-Hydrology, 12587 Berlin, Germany, holzbecher@igb-berlin.de

A common characteristic of many continental margin sedimentary deposits is that sulfate (SO42-) with seawater concentration penetrates several meters to more than 100 meters down into the sediment porewater. The sulfate will be reduced to H2S, in general, by oxidation of organic matter mediated by the activity of sulfate-reducing bacteria [1]. The sulfate concentrations in the sedimentary porewaters show constant or continuously decreasing gradients from the surface down to the sulfatereduction zone where the sulfate pool becomes completely exhausted and methane (CH4) concentrations are high in the underlying pore space. Thus, the anoxic methane oxidation is the basic process which creates the chemical potential for the sulfate reduction [2].

However, changes in this gradient have been

observed several meters below the surface in sediment cores from different locations; anoxic sulfide oxidation in surface layers and nonlocal transport mechanisms of porewater or submarine landslides have been mentioned to be responsible for porewater gradient changes [3, 4]. Our studies of a sediment core from the Marmara-Sea also show a remarkable change in this gradient. The results indicate that a long-term constancy of diagenetic processes cannot be assumed at all times. Methane emanations from the seafloor as observed at other locations along the deeper Ganos Fault give evidence that the sulfate-methanereaction zone (SMRZ) already reached the sediment water interface [5]. We therefore suggest an evolution of a time-dependent transient state for this reaction zone.

Figure 1: An overview of the worklocation in the Marmara Sea (left). The local tectonic situation and the position of core KLG 72 are shown in the picture above.

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The subject of our study is to show that such changes could be caused by tectonic activity (e.g. earthquakes) if they influence the respective flux of one of the involved reaction partners. For this purpose we present data mainly from one gravity core (72 KLG) which was recovered from the Ganos Fault, a tectonically very active fault zone in the Sea of Marmara (Fig. 1).

The results from this sediment core revealed a porewater pattern which can be subdivided into four different sections (Fig. 2): 1) a relic steady-state diffusion zone in the upper part of the core 2) a transition zone where sulfate decreases with a steeper gradient 3) the sulfate-methane-reaction zone and 4) the methane-supply zone.

Our study starts with a steady-state concentration profile for sulfate, which is then gradually consumed by a front of rising methane caused by an oversupply of this gas. From the sulfate concentrations measured in the upper 3 m of the core (with a high correlation coefficient of 0.98) a linear steady-state profile results which, after extrapolation, reaches zero concentration at a depth of 32.2 m. This is equivalent to a gradient of 0.101 g/l 路 m (0,1 mmol/l 路 dm) for sulfate.

It is assumed that after an extraordinary event (earthquake) the methane flux increased remarkably, reached that toe-point and, reacting with sulfate in the SMRZ, which has gradually been rising upward since that time.

The transport mechanisms within the sediment column for methane is advection, whereas sulfate is transported by diffusion. Implementation of this data-set into a computer based diffusion-advection model estimates a velocity of 1.8 cm/a for the SMRZ-rise. The determined time period for the SMRZ to cover the distance from 32.2 m to the current position (~ 4-5 m) is 1550 years.

Many earthquakes have been reported in the Bosporus region which could possibly have affected the Marmara Sea as well and thus opened new pathways for the rise of methane from the deeper subsurface [6, 7]. One major event within the Marmara Sea is well documented in 447 a.D.; this is almost identical to the initial time of 450 a.D. as calculated by our model. The epicentre of the earthquake lay in the direct vicinity of the site where our core was taken. The remarkable fact that our modelled time frame coincides with the date of a large local earthquake leads the authors to believe that the SMRZ migration can indeed be initiated by tectonic events.

Figure 2: Concentration profiles of SO42- and CH4.

In (1) SSDZ = relic steadystate diffusion zone, TZ = transition zone, SMRZ = sulphate-methanereaction zone, MSZ = methane-supply zone. In (1) the TZ is characterized by a steep decrease of the sulfateconcentration; the methaneconcentrations instead increase drastically within the SMRZ [2].

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References [1] Widdel F. (1988) Microbiology and ecology of sulfate- and sulphur reducing bacteria.

In: Biology of Anaerobic Microorganisms (ed.

Zehnder A.B.J.). Chap. 10, pp. 469-585, John Wiley & Sons, NY. [2] Niewöhner C., Hensen C., Kasten S., Zabel M., Schulz H.D. (1998) Deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the up welling area off Namibia, Geochim.

Cosmochim. acta, 62, No. 3, 455-464.

[3] Fossing H., Ferdelman T., Berg P. (2000) Sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation (South-East Atlantic off Namibia), Geochim. Cosmochim. Acta, 64, No. 5, 897-910.

[4] Zabel M. and Schulz H.D. (2001) Importance of submarine landslides for non-steady-state state conditions in pore water systems - lower Zaira (Congo) deep-sea fan, Marine Geology, 176, 87-99.

[5] Halbach P. , Kuscu I., Inthorn M., Kuhn.T, Pekdeger A., Seifert R. (2001) Methane in sediments from the deep Marmara Sea and is relation to local tectonic structures, in: N.Görür (Ed.), NATO advanced Research Papers: integration of earth sciences research on the 1999 Turkish and Greek earthquakes and needs for future cooperative research, TÜBITAK, Istanbul, (in print).

[6] Ambraseys N.N. and Finkel C.F. (1991) Long-term seismicity of Istanbul and of the Sea of the Marmara Sea region, Terra Nova, 3, 527-539.

[7] Stiros St.C. (2001) The 365 AD Crete earthquake and possible seismic clustering during the fourth to sixth centuries AD in the Eastern Mediterranean; a review of historical and archaeological data, Journal of Structural Geology, 23, 545-562.

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Methane-derived carbonate mineralisation in the northwestern Black Sea Reimer A. (1), Peckmann J. (2), Reitner J. (1) (1) Geowissenschaftliches Zentrum der Universität Göttingen, Abteilung Geobiologie, Goldschmidtstraße 3; D-37077 Göttingen, Germany (2) Postgraduate Research Institute for Sedimentology, University of Reading, Whiteknights, Reading, RG6 6AB, UK

During the GHOSTDABS expedition with RV Logachev in July/August 2001, methane seeps at the shelf and slope of the northwestern Black Sea were investigated. Seep areas close to the Dnepr Canyon were found to be sites of intense carbonate deposition.

In the oxic zone of the shelf and upper slope, carbonate precipitation is confined to the anoxic sediment where layered carbonate crusts and flat plates form. Here, seepage induces intergranular precipitation of microcrystalline high-Mg-calcite and aragonite. The cemented siliciclastic sediments may contain mytiloid or dreissenoid bivalves and carbonate concretions that consist of displacing elongated aragonite crystals.

At about 180 m water depth, in the upper anoxic zone of the slope, widespread large carbonate plates occur. Small irregular chimneylike structures arise from these basal plates.

Carbonate plates are tilted and broken, obviously due to strong erosional forces of coastal currents in this water depth.

Within the deeper permanent anoxic slope, chimney-like build-ups are found that are penetrated by active seepage. During the ‘Jago’ submersible dives down to a depth of 400 m, towers up to 4 m in height have been discovered. The carbonate minerals forming the chimneys are high-Mg-calcite and aragonite.

High-Mg-calcite occurs in a microcrystalline variety (micrite) containing 11 to 14 mol% MgCO3. Aragonite mostly forms fibrous cement crystals as isopachous layers or botryoids (Peckmann et al. 2001). Microcrystalline aragonite is less common. The exterior surfaces of the chimneys mostly consist of aragonite cement, indicating that aragonite preferential-

ly forms in contact with seawater. The chimneys internal fabric is patchy with highly irregular transitions from micrite clusters to aragonite cement. A volumetrically significant portion of the chimneys is represented by irregularly distributed, inter-connected pore space, but no central channel exists. The carbonates are extremely depleted in 13C. Stable isotope analyses yielded δ13C values that range from -27 to –41‰ PDB for high-Mg-calcite and from –26 to –38‰ PDB for samples of aragonite cement. These low δ13C values reveal that the carbonates predominantly derive from the microbial oxidation of methane.

The chimneys exterior surfaces, internal cavity walls, and veins are heavily colonised by the microbial consortium that presumably performs anaerobic methane oxidation.

Features of the exterior surface areas at the top part of many chimneys are hollow spheres.

Their walls consist of a thin, porous layer of aragonite, which is covered by a black microbial mat. Initially hollow spheres in older portions of chimneys tend to be filled by authigenic carbonates from the aragonite wall towards the interior.

When sampled with the submersible, the hollow spheres have been found to be partly filled by gas. Due to the spherical shape, the colonisable surface is maximised. Substratum for microbial metabolism, methane, is provided from the interior of the sphere, and exchange with seawater, which is important for e.g. the supply of sulphate, can proceed most efficiently. δ18 O values of the carbonates, ranging from +2.0 to +0.2‰ PDB, are rather close to δ18 O values of dissolved seawater bicarbonate (Lein et al., 2002), and 87Sr / 86Sr ratios of microcry-

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stalline carbonate (mean 0.70927) and aragonitic cement (mean 0.70918) indicate that Sr is derived from the ambient seawater (mean 0.70917) and not from seepage fluids.

The methane seeps in the northwestern Black Sea are sites of a pronounced biogeochemical cycling of carbon. The carbonates as products of microbially mediated reactions exhibit signatures of both deep-seated and marine sources.

Figure 1: Sketch of a carbonate chimney from the permanent anoxic zone of the northwestern Black Sea slope.

Notice black spherical structures on top of the chimney.

Height of the Chimney is appr. 1.5 m.

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References Peckmann J, Reimer A, Luth U, Luth C, Hansen B T, Heinicke C, Hoefs J, Reitner J (2001) Methane-derived carbonates and authigenic pyrite from the northwestern Black Sea. Marine Geology 177, 129-150.

Lein A Y, Ivanov M V, Pimenov N V, Gulin M B (2002) Geochemical Characteristics of the carbonate constructions formed during microbial oxidation of methane under anaerobic conditions. Microbiology, 71, 1, 78-90.

Translated from Mikrobiologiya, 71, 1, 89-103.

An Introduction to INGGAS: INtegrated Geophysical characterisation and quantification of GAS hydrates.

Reston T. (1), Gajewski D. (2), H端bscher C. (2), Fl端h E. (1), Bialas J. (1), Villinger H. (3), Theilen Fr. (4), and the INGGAS Group (1) GEOMAR Research Centre, Kiel, Germany (2) University of Hamburg, Germany (3) University of Bremen, Germany (4) Christian-Albrechts University, Kiel, Germany

The quantity and the distribution of gas hydrates along the continental margins has important implications for slope stability, for climate change, for offshore engineering and potentially for future energy resources.

However, the main method for remotely determining the presence of gas hydrate remains the imaging of a bottom-simulating reflection (BSR), although this only indicates the presence of hydrate where it is underlain by free gas.

Furthermore, the distribution of hydrate volumes within the sediment has important implications for the shear strength of the sediment. Finally, the fluid flow regime associated with hydrate formation and dissociation remains poorly understood. To address

these issues, the INGGAS project set out to develop geophysical equipment necessary to investigate - the nature, structure, distribution and quantification of gas hydrate fields in all water depths and methane-bearing permafrost soils in shallow water environments.

Questions of interest include the reservoir characteristics of gas hydrate bearing sediments and the underlying free gas zone, the thickness of the transition between them, the rate at which this equilibrates, the amount of free gas present beneath it and how gas hydrates can be identified in the absence of a BSR. - physical properties (P- and S-wave velocities,

Figure 1: Schematic illustration showing how the equipment developed within INGGAS can be used for interdisciplinary investigations of gas hydrates. To avoid confusion, only main links are shown.

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shear moduli) of sediments within and beneath the gas hydrate zone. This has implications for the amount and distribution of gas hydrates and of free gas and also for slope stability.

- the different physical, sedimentological and tectonic environments in which gas hydrates develop and accumulate. Parameters include methane flux, heat flux, water depth, deformation rates and fluid flow rates (hence pore pressure).

INGGAS consists of five integrated Subprojects (Figure 1): 1) INGGAS-HISS. This set out to develop an integrated seismic system for gas hydrate research. The key aspects are the use of ocean bottom sources to generate the shear waves needed to determine, in conjunction with P-waves, the physical properties of the hydrated and the free gas zone. Two different ocean bottom sources were successfully tested during a cruise with the RV Sonne in March 2002. This will reveal the amount and distribution of both gas hydrates and free gas within the sediment, and will allow assessment of the influence of gas hydrate and the underlying gas zone on slope stability. The Subproject also will acquire a high frequency towed source (a watergun) for high resolution investigations of hydrates.

2) INGGAS-OBS This Suproject has constructed and tested the 3-C ocean bottom seismometers needed for multi-component ocean floor seismology, and in particular the recording of S-waves. These will in conjunction with more traditional P-waves, allow the physical properties of the subsurface to be fully characterised, revealing the amount and distribution of gas hydrates within the sediments in the interwell gap. Testing of the instruments has taken place offshore Spitsbergen in two places where gas hydrates are known to exist (one with a BSR, one without), offshore Peru in March 2002, and will further take place off Norway in Summer 2002.

3) INGGAS-DEEP TOW: This Subproject has developed a deep-towed streamer system

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rated for ocean depths. Lowering the streamer to the seafloor, reduces the size of the Fresnel Zone and hence increases the spatial resolution. Previous studies have shown the benefit of such systems for imaging small-scale structures such as faults that are likely to be important fluid conduits, and for revealing the fine structure of the BSR. The streamer has been successfully tested off Peru in March 2002 (see contribution from Breitzke and others). Incorporated within the deep tow system is a navigation system rated for ocean depths, allowing accurate location of the streamer. This navigation system can also be used for the side-scan sonar to be acquired within the OMEGA project.

4) INGGAS-FLUX: This Subproject set out to develop and construct low-cost disposable pore pressure probes and an extended heat flow probe. Both are essential to characterise the fluid flow regime associated with gas hydrates, particularly in regions of active deformation. After data collection, the pore pressure probe will release a data logger to the surface, from where it will transmit the data via satellite link to the lab. The extended heat flow probe (up to 6 m penetration) will improve heat flow measurements needed to determine fluid outflow rates. As gas hydrates form from gas and water rising from depth, understanding the fluid regime of gas hydrates is a pre-requisite for understanding gas hydrate formation.

5) INGGAS-NATLAB: This subproject is concerned with the study of shallow gas-bearing sediments in the Baltic Sea using some of the geophysical techniques similar to those within the rest of INGGAS. In particular, the main objective of the project is the assessment of shear waves in the sea floor under in-situ conditions and the correlation of shear wave velocities with sediment properties. The shear wave velocity measurements are based on Scholte waves, which are also observable in the lower part of the water column and thus assessable by a continuously towed streamer just above the sea floor.

Raman Spectroscopic measurements of gas hydrates Schicks J., Lüders V., Möller P. GeoForschungsZentrum Potsdam, AB 4, Telegrafenberg, 14473 Potsdam, Germany

The knowledge of the conditions for gas hydrate formation, as well as their stability fields and phase boundaries are necessary for their fundamental understanding. The formation of pure gas hydrates under various P-T-xconditions and the phase diagrams of these systems are well known, whereas phase diagrams of mixed gas hydrates based on experimental data have not been published yet. Mixed clathrates behave different from the pure endmembers and calculated phase relationships often deviate considerably from experimental data. Therefore, the aim of our research project is to synthesise and analyse mixed gas hydrates and use the experimental data obtained for the construction of phase diagrams. For these purposes an experimental set-up has been developed, which allows the observation and documentation of the formation, growth and decomposition of mixed gas hydrates as well as the analysis of the gaseous and solid phases under approached equilibrium conditions via Raman Spectroscopy for the determination of the phase composition.

The main item of the experimental device is the pressure cell (Fig. 1), which can be used in the temperature range between –27 °C and + 80 °C and in the pressure range between 0.1 and 10.0 MPa. The small sample volume (0,4 cm3) and the all-around cooling of the sample obviate a gradient of temperature.

A quartz window permits the analysis of the phases by Raman Spectroscopy and the observation of the sample in the cell or the documentation of formation or decomposition processes with a CCD-camera.

Figure 1

For testing the functionality of the experimental set-up the well known system methane-water has been chosen. The shift of the peak position, the split of the band and the broadening of the band enable a clear identification of methane trapped in the clathrate lattice [1].

Preliminary results in the system CH4-CO2-H2O indicate that also CO2 gets incorporated into a hydrate lattice and the bands are broadened and the peak position shifts similarly (Fig. 2).

Figure 2

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Multitudinous measurements under variable conditions are necessary to construct a phase diagram: at constant gas composition and total pressure the temperature is varied and the establishing composition of gas and solid phases are registered. The results obtained for the system methane-water correspond well to literature data [2] (Fig. 3).

Figure 3

In addition to the actual measurements on the system CH4-CO2-H2O the systems CH4-N2-H2O and CH4-H2S-H2O will be studied systematically with the aim to determine the clathrate-solidus as a function of the gas composition, the salinity of the aqueous phase, pressure and temperature.

References [1] Subramanian, S; Kini, R.A.; Dec, S.F.; Sloan, E.D.; Chemical Engineering Science 55; 2000;1981-1999 [2] Sloan, E.D.; Clathrate Hydrates of Natural Gases; Marcel Dekker,Inc.;1997; New York, Basel

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Development of a Methane Biomicrosensor for Deep Sea Applications Schmidt-Brauns J., de Beer D. Max-Planck-Institute for Marine Microbiology, Bremen, Germany

The main objective of this project is to adapt an existing methane biomicrosensor for deep sea applications. Microsensors are needle shaped glass electrodes with a sensitive tip of 1-20 Âľm diameter, depending on the type. In the conventional microsensors, the analyte is specifically and directly detected by amperometric or potentiometric means. In biosensors an extra step is involved: the conversion of the substrate by bacteria immobilised in the sensor tip. Methane detection using a biosensor is based on the co-conversion of oxygen by methane oxidizing bacteria (CH4 + O2 -> CO2 + H2O) and change in oxygen concentration is measured with an integrated oxygen sensor.

The methane biomicrosensor (Fig. 1) consists of three parts: an oxygen microsensor and two glass capillaries. The inner glass capillary serves as oxygen reservoir and the outer capillary contains methanotrophic bacteria.

The sensor is based on a counterdiffusion principle. Methane oxidizing bacteria placed in the outer glass capillary utilize oxygen from the internal oxygen reservoir when methane from the exterior diffuses through the tip membrane.

The external partial pressure of methane determines the rate of bacterial oxygen consumption within the sensor, which in turn is reflected by the signal from the oxygen microsensor. The higher the external partial pressure of methane, the more oxygen the bacteria consume, subsequently a lower signal is measured (Fig. 2).

Figure 2: Functioning principle: The partial pressure of oxygen measured in the two situations is indicated by the arrows. The sensor is exposed to a high (A) or low (B) partial pressure of methane.

Figure 1: Schematic drawing of a methane biomicrosensor.

Left: entire sensor; Right: tip section. From Damgaard and Revsbech, 1997.

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Deep sea (100-1500 m) biosensor manufacture and use will have to account for changes in pressure in temperature.

Pressure will affect mainly the inner gas filled capillary. A new initiative to make this capillary pressure resistant will be to fill the capillary with oxygen saturated silicon oil instead of pure gas.

Low temperatures at working depths will result in a reduced bioreactive sensitivity of most methanotrophic bacteria. A second initiative is to utilize Methylosphera hansonii, a psychrophilic aerobic methane oxidizing species which was isolated from a seawater lake in Antarctica.

Another possibility to overcome the temperature problem is to enlarge the reaction zone inside the biosensor to allow more conversion.

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Simulation of the oceanic gas hydrate removal using the mammoth-pump-principle Schultz H.J., Deerberg G., Schl端ter S., Fahlenkamp H. Fraunhofer-Institut f端r Umwelt-, Sicherheits- und Energietechnik UMSICHT, Essener Str. 99, 46047 Oberhausen, heyko-juergen.schultz@umsicht.fhg.de

Conceptual formulation and goal of this study Within the scope of a financially supported research project (BMBF/Project 03G0550A), the task is to develop a computer-program to describe the destabilsation and controlled extraction of oceanic gas hydrates. The feasibility of controlled upflow of destabilised gas hydrates by the mammoth-pump principle in concentric tube arrangements is the main objective of the study. Basic aspects of gas hydrate destabilisation and flow mechanisms are considered. The feasibility and process safety are points of interest.

The examination is based on realistic data and numerical simulations. A software code will be written for the simulation of the steady state and the dynamic process operation.

Introduction In the last years, the gas hydrate topic is of rising economical and ecological interest. On the one hand, the controlled use of gas hydrates as a ressource could guarantee the worldwide energy supply for a long time. On the other hand, the instability of this ressource depicts an exposure, i.e. an uncontrolled, climate affecting release of gas (hydrocarbons, mainly methane) from gas hydrates has to be avoided. Because of this, the controlled extraction of gas hydrates is not only of economical interest but also of ecological and societal relevance in view of the preventive, climate-saving removal of instable hydrate fields.

controlled and safe upflow of instable oceanic gas hydrates and hydrocarbons, respectively.

The main elements of this approach are: - thermal stimulation of gas hydrates in oceanic sediments with heated sea-water to release hydrocarbons, - concentric tube arrangement for the purpose of transporting heated sea-water in the inner tube and mixtures of water, hydrate particles, sediment and gaseous hydrocarbons in the outer an-nulus by the mammoth-pumpprinciple.

Figure 1 shows a sketch of the principle. Thermal stimulation with heated sea-water to release hydrocarbons from instable gas hydrates, particularly methane, is the method of choice for the technical approach. The main advantages are: - no additional chemicals are required, - the necessary transport of energy to the deposit can directly be integrated in the process.

The mammoth-pump-principle seems to be suitable. Two concentric pipes will be brought down. The warm water will be pumped downwards through the inner tube, while water and released gas will stream upwards through the outer annulus (or vice versa). The flow of downstreaming water will be driven only by the difference of density between the fluids in the inner tube and the outer annulus. This density difference is equivalent to a pressure difference between the head of the inner tube and outer annulus, sufficient enough to pump the warm water all the way down to the deposit.

Description of the extraction apparatus The main research objective is the feasibility of applying the mammoth-pump-principle to the

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 Figure 1: Application of the mammoth-pump-principle to controlled and safe upflow of oceanic gas hydrates

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15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Outer tube, annulus (here: upcomer) Inner tube (here: downcomer) Hydrate reservoir, deposit Head, sea vehicle Sea surface Water, water column Sea floor sediment Fresh water supply Liquid overflow Product (gas) withdrawal Gas-partial flow, energy-generator-feed Energy-generator Hot burning gases, heat transfer medium Offgas, waste heat usage Upcoming gas, product Upcoming solid (sediment, hydrate) Oil Separation apparatus for solid Solid withdrawal Separation apparatus for oil Oil withdrawal Cycle pump (start phase) Solid withdrawal pump Fresh water feed pump Oil withdrawal pump Liquid overflow valve Product (gas) withdrawal valve Gas-partial flow valve Heat exchanger

Reactor simulation The transient implementation of the reactor simulation is realised by a multi-area-cellmodel. Figure 2 shows the 4 areas head, down, upcomer and bottom. Each area can be devided into N area-dependent, ideal mixed cells.

A dynamic balancing for each cell of the reactor areas follows. In this context, the balance equations of components (mass), energy and momentum are obtained as a differential equation system and added by algebraic (approximation) equations. This results in a differential-algebraic-equation-(DAE-)system that can be solved by a numerical solver.

Thus, the simulation provides with time-dependant pressure-, concentration-, temperatureand velocity-profiles. Through dividing the four reactor areas into cells, the profiles are presentable location-dependant, too.

Summary and outlook The goal of this activity is to develop a simulation-program, that describes the destabilisation and controlled extraction of oceanic gas hydrates. Innovative removal technologies are necessary for the safe, environmentally responsible examination of gas hydrate. The study will deliver basic knowledge of a possible recovery technology for (instable) gas hydrates, which might be successfully realised in the near future. With the help of the simulation code, the evaluation of the proposed flow process will be possible. This evaluation consists of two main parts, technical feasibility and process safety / risc evaluation. Parameter studies will give further information about reactor-design adaptations. Hence, beside the technical feasibility and safety considerations, the objective of the study is the estimation of energetic efficiency of the gas hydrate winning process, i. e. the ratio of energy output (energy content of hydrocarbon gas) and energy input (energy loss to surrounding and energy effort for thermal stimulation).

The software code will be founded on a mathematical model of the flow process. This model incorporates the conservation balances of mass, energy and momentum. The derived equation system will be completed by data, assumptions, and models of the investigated single phenomena (bubble flow, etc.). Multiple interactions between relevant physical quantities of the flow process, have to be considered in this context. The simulation program will be a suitable tool for evaluating the described technical approach.

Figure 2: Multi-area-cell-model for the gas hydrate extraction reactor

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Program for the simulation of gas hydrate equilibrium Schultz H.J., Deerberg G., SchlĂźter S., Fahlenkamp H. Fraunhofer-Institut fĂźr Umwelt-, Sicherheits- und Energietechnik UMSICHT, Essener Str. 99, 46047 Oberhausen, heyko-juergen.schultz@umsicht.fhg.de

Conceptual formulation and goal of this study Within the scope of a financially supported research project (BMBF/Project 03G0550A), the task is to develop a computer-program to describe the destabilisation and controlled extraction of oceanic gas hydrates. In order to predict the thermodynamic processes in a gas hydrate deposit or an extraction apparatus, essential knowledge of hydrate formation/ decomposition conditions is required. The knowledge of the hydrate stability is important for the controlled destabilsation inside oceanic deposits as well as for the rebuilding-prevention of gas hydrate in the extraction apparatus (plug-danger). Hence, a thermodynamic module for the calculation of hydrate equilibrium states (single- and multihydrate-formersystems) has been implemented in a first step.

Basics Introduction In the last years, the gas hydrate topic is of rising economical and ecological interest. On the one hand, the controlled use of gas hydrates as a ressource could guarantee the worldwide energy supply for a long time. On the other hand, the instability of this ressource depicts an exposure, i.e. an uncontrolled, climate affecting release of gas (hydrocarbons, mainly methane) from gas hydrates has to be avoided. Because of this, the controlled extraction of gas hydrates is not only of economical interest but also of ecological and societal relevance in view of the preventive, climatesaving removal of instable hydrate fields.

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Used Model The literature provides with results of different calculation programs for the estimation of equilibrium conditions during hydrate formation [1], [2]. For this study it is necessary to implement a thermodynamic program, that can be integrated in a superior program-environment as a sub module.

The developed simulation tool is based upon the fundamental considerations of van der Waals und Platteeuw [3]. Today, extended and improved approaches exist, e.g. for multicomponent-systems.

In a system of equilibrium state, the pressure, the temperature and the chemical potential of all components in the participating phases are equal. The estimation of the thermodynamic equilibrium of the overall sytem is realised by the determination of the chemical potentials of water in the hydrate phase and water in the liquid phase.

The potentials are referred to a common reference state, i.e. the fictive modification β that is thermodynamic unstable and describes a completely empty hydrate lattice. Thus, the equilibrium condition can be written as: (1)

Equation (1) results in: (2)

The potential differences in equation (1) are calculated with further approaches. The development of the referring formulas and correlations can exemplarily be found in [1], [2], [3] and shall not be given here in detail. In the generated thermodynamic simulation program, equation (2) is solved iteratively by giving a temperature value as the equilibrium temperature and computating the associated pressure value.

Simulation results The used model provides the computation of single- but also of multi-component gas hydrate equilibrium states with high accuracy. The model parameters (component dependent Kihara-parameters) are mainly fitted to the extensive experimental data of Nixdorf [2].

First, the respective parameters were fitted to one-component-systems. These parameters showed good results for multi-componentsystems, too. To demonstrate the computation results in an example, the simulation for pure methane-hydrate is compared to the experimental data of Nixdorf in figure 1. The mean deviation for the shown range is 0,56%.

During the equilibrium calculations, the Langmuir-constant is computed. In the implemented simulation program, the Langmuirconstant can be computed by three different methods, i.e.: - a potential-function (Kihara-interactionpotential) [3], [2], [4], - an approximation function with constant-

data by Parrish and Prausnitz [4] - an approximation function with constantdata by Munck, Skjold-JĂśrgensen and Rasmussen [5].

According to this, a comparison between the three methods is possible.

Summary and outlook Within the scope of a research project for the development of a simulation-program, that describes the destabilisation and controlled extraction of oceanic gas hydrates, a modular, thermodynamic program (â&#x20AC;&#x153;HYDRATPACKâ&#x20AC;?) for the computation of one- and multi-component gas hydrate equilibrium systems has been implemented. Through this, component data can be calculated by different equations of state and the Langmuir-constant, necessary for the equilibrium considerations, can be computed by three different selectable methods. The parameter fitting took place with the aid of extensive experimental data of Nixdorf [2] and other researchers. The simulation tool delivers good results with the computation of gas hydrate equilibrium data.

Further laboratory experiments concerning hydrate formation, inhibitor-influence etc. will lead the developed simulation tool HYDRATPACK to predict the formation conditions in gas pipelines. HYDRATPACK represents a contribution to the rising interest in the gas hydrate topic. The poster will show further comparisons between experimental and simulation data, also for multi-component-

Figure 1: Comparison between experiment and simulation for methane-hydrate.

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systems. Additional to this, a comparison between different methods of calculating the Langmuir-constant will be given.

Literature [1] Sloan, E. D. Jr.: Clathrate Hydrates of Natural Gases, Marcel Dekker Inc., New York 1998 [2] Nixdorf, J.: Experimentelle und theoretische Untersuchung der Hydratbildung von Erdgasen unter Betriebsbedingungen, Dissertation TH Karlsruhe, 1996 [3] Waals, J. H. van der; Platteeuw, J. C.: Clathrate Solutions, Adv. in Chemical Physics, In-terscience Publishers Inc., New York 1958 [4] Parrish, W. P.; Prausnitz, J. M.: Dissociation pressures of gas hydrates formed by gas mixtures, Ind. Eng. Chem. Proc. Des. Develop. 11 (1972) 1, S. 26-35 [5] Munck, J.; Skjold-Jรถrgensen, S.; Rasmussen, P.: Computations of the Formation of Gas Hydrates, Chem. Eng. Sci. 43 (1988) 10, S. 2661-2672

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Gases and dissolved carbon compounds in the north-western Black Sea – concentrations and isotopic compositions (I+II) Seifert R. (1), Blumenberg M. (1), Pape T. (1), Peterknecht K. (1), Thiel V. (1), Schmale O. (1), Sültenfuß J. (2) , Rhein M. (2), Michaelis W. (1) (1) Institute of Biogeochemistry and Marine Chemistry, University of Hamburg, Bundesstraße 55, 20146 Hamburg (2) Institute of Environmental Physics/Oceanography, University of Bremen, Kufsteiner Str. 1, 28359 Bremen

For a comprehensive investigation of gashydrates and gas/fluid seeps of the northwestern Black Sea the German research Project GHOSTDABS (Gas Hydrates: Occurrence, Stability, Transformation, Dynamics, and Biology in the Black Sea) in cooperation with Rumanian, Russian and Ukrainian scientists was founded. A research cruise using the Russian RV “Professor Logachev” was performed in summer 2001. Deploying a rosette water sampling system more than 100 water samples were taken from the water column (0 – about 2.070 m water depths). Additionally, a unique set of sediment push cores as well as near bottom water and gas samples were taken with the German submersible “JAGO” between 65 and 325 m water depths.

The secluded ecosystem of the Black Sea represents an extraordinary research area. As a result of the particular geo- and hydrological settings of the Black Sea basin the ventilation of deeper water masses is restricted and a permanently anoxic zone has evolved during the last 7000 - 9000 years (Boudreau and Leblond, 1989).

The downward flux of particulate organic matter from the brackish surface waters leads to an accumulation of reduced inorganic and gaseous end products (e.g. NH4+, HS –, CH4 , H2 ) and highly reduced organic compounds in the deeper, more saline parts of the water column (Karl and Knauer, 1991). Especially at the north-western continental slope a great number of distinct methane-rich seeps supplying enormous amounts of gas were observed (Egorov et al., 1998). Moreover, recent studies

in the central Black Sea and off the Crimea Peninsula provide clear evidence for the occurrence of mud volcanoes. For the first time gas hydrates were illustrated at the studying area.

To classify the sources of gases and carbon coumpounds in waters of the Ukrainian shelf area numerous analyses of C1 – C4 hydrocarbons, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and stable carbon isotopic signatures (δ13C) of methane were performed. Furthermore, contents of noble gases were determined for selected water samples.

In general extremely elevated amounts of hydrocarbons were found in all anoxic sediment and water samples. Moreover, for concentrations and isotopic compositions of methane interesting distribution patterns were observed in these environments.

In a permanently anoxic non-seep related sediment sample (320 m water depth, Fig. 1) CH4 concentrations increased with depth. At the sediment-water transition zone 21,5 [µmol CH4 L–1 sediment] were measured. Preliminary results of stable carbon isotopic measurements revealed continuous relative enrichments of 13 CH4 with decreasing sediment depth most probably due to AMO between 13 and 1 cm. δ13CH4 values of five near bottom water samples from different water depths typically ranged from -51,5 to -57,2‰. In contrast, gas bubbles venting at same locations were relatively depleted in 13CH4 (- 58,5 up to -68,2‰).

Concentrations of methane in anoxic water samples decreased with decreasing water

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depth. Highest values (> 18 µmol L– 1) were observed at 1.700 m water depth and δ13 CH4 measurements indicate diverse microbial processes within the water column. Relative enrichments in 13CH4 of different water depths within the anoxic zone are most probably due to varying communities of methane oxidizing microorganisms.

Results for dissolved noble gases revealed supersaturation with respect to atmospheric equilibrium in deeper waters (Fig. 2). This enrichment of He and especially Ne might be related to seep activity or gas hydrate formation in the sediments.

Figure 2: Concentrations of noble gases in waters of the Ukrainian continental slope (water samples stations 65+66); (dots = δ3He, squares = δHe* (δHe, Ne corrected) and triangles = δNe).

Another objective of our field studies are the concentration and isotopic compositions of specific noble gases within the water column. XXX water samples were analyzed for 3He, 4He and Ne

Literature Boudreau B. and Leblond P.H. (1989) A simple evolutionary model for water and salt in the Black Sea. Paleoceanography 4, 157-166.

Figure 1: Concentrations and carbon isotopic signature of methane in a permanently anoxic sediment (1-19 cm depth) on the Ukrainian continental slope; (squares = concentrations, dots = δ13CH4).

Egorov V.N., Luth U., Luth C. and Gulin M.B. (1998) Gas seeps in the submarine Dnieper Canyon, Black Sea: acoustic, video and trawl data. In: Methane gas seep explorations in the black Sea (MEGASEEBS), Projekt Report (U. Luth, C. Luth and H. Thiel, eds.). Ber. Zentrum Meeres- u. Klimaforsch. Univ. Hamburg, Reihe E, 14, 11-21.

Karl D.M. and Knauer G.A. (1991) Microbial production and particvle flux in the upper 350 m of the Black Sea. Deep-Sea Research 38 (Suppl. 2) S921-S942.

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Biomarkers and biogeochemical activity in methane fed microbial mats of the Black Sea. Seifert R. (1), Nauhaus K. (2), Thiel V. (1), Blumenberg M. (1), Widdel F. (2), Michaelis W. (1) (1) Institute of Biogeochemistry and Marine Chemistry , University of Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany (2) Max Planck Institute for Marine Microbiology, Celsiusstrasse, 28539 Bremen, Germany

During the GHOSTDABS–cruise in July 2001, we could recover samples of massive microbial mats from the sea floor of the Black Sea using the German submarine ‘JAGO’ operated from onboard the Russian R.V. ‘PROFESSOR LOGACHEV’. The sampling location south-west the Crimea peninsula was at 230m water depth, where huge microbial reefs thrive within the anoxic water body at active methane gas seeps. These reefs are composed by an assemblage of individual structures emerging up to 4m from the sea floor and composed of cm- to dm-thick microbial mat which are internally stabilized by carbonate precipitates (Fig. 1).

The unique sample set of almost sediment free massive microbial mats performing combined anaerobic methane oxidation (AMO) and sulphate reduction (SR) allowed detailed biogeochemical studies not possible so far.

Lipid analyses of the macroscopically different types of microbial mats (Fig. 1) – carbonate associated brownish green mat (type I); massive pink mat (type II); gray to black colored outer layer (type III) – revealed substantial differences between these three features regarding both their lipid composition and the carbon isotope signature of individual compounds.

To obtain information on the biochemical processes, we incubated living microbial mat in vitro under strictly anoxic conditions in a defined mineral medium and with 13C-enriched methane as the sole organic substrate (16 mM SO42-, 1.6 mM CH4). The microbial mats reduced sulphate rapidly and produced sulphide. Moreover, the incorporation of methane derived 13C into the biomass could be observed for the bulk mat as well as for individual lipids.

Figure 1: Schematic cross section of a microbial formation discovered in the Black Sea.

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A novel benthic chamber for long-term in situ observation and experiments (LOTUS) Sommer, S. (1), Pfannkuche, O. (1), Linke, P. (1), Gust, G. (2), Gubsch S. (2) (1) GEOMAR, Research Center for Marine Geosciences, 24148 Kiel, Germany (2) Ocean Engineering 1, Technical University Hamburg-Harburg, 22305 Hamburg, Germany

There is growing necessity to conduct longterm benthic observations and manipulative experiments under in situ conditions. During the LOTUS project (www.gashydrate.de) within the German gas hydrate research initiative a novel benthic chamber to be integrated into the GEOMAR Lander was designed to identify biogeochemical processes controlling the composition and decomposition of surficial gas hydrates. During long-term in situ measurement series in gas hydrate containing sediments i. variability of benthic carbon turnover, ii. variability of fluxes of oxygen, methane and sulphide across the sediment water interface and iii. pathways of benthic carbon transfer will be determined.

The sampling area of the new circular chamber (Figure 1) amounts 706.5 cm2 to obtain a large volume of sediment for latter on-board analy-

sis, to account for mesoscale heterogeneity, and to provide a large area through which fluid and gas flow across the sediment water interface is possible.

In order to record long-term variability of benthic turnover in semi-closed chamber systems it is of crucial importance to maintain the oxygen supply at natural levels and to avoid severe oxygen depletion. Thus, to compensate for the total oxygen consumption of the enclosed sediment community a gas exchange system (Figure 1) was designed. This system facilitates oxygen transfer from a reservoir (approx. volume 35 l) containing saturated seawater into the benthic chamber across silicone membranes.

Figure 1: Scheme of the benthic chamber and the gas exchange system.

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The design of this system is based on the counter-current principle as realised in gills of e.g. fish, where oxygen enriched blood and oxygen depleted blood flows counter-currently along a membrane, which is permeable for oxygen.

Oxygen transfer is mediated along a concentration gradient via diffusive transport. The gas exchange system tested possesses five membranes with a total gas exchange area of 392.7 cm 2, however more membrane stacks can be integrated into the system. The thickness of the membrane is 0,125 mm. Water flow within the chamber- and reservoir circuits is facilitated

by Seabird pumps.

For tests two chambers were integrated into a lander, a control chamber without a gas exchange system and a chamber fitted with such a system. The oxygen concentration in both chambers and the reservoir was surveyed in water samples obtained by an automatic syringe water sampler at defined time intervals (Figure 2). The silicone membrane of the gas exchange system is not only permeable for oxygen but also for methane and probably for other gases. Thus, this system in combination with the reservoir might be promising for the determination of diffusive fluxes of gases such as CH4 and CO2 across the sediment water

interface.

Advective and diffusive transport rates of solutes and micro-particulates across the sediment water interface are highly susceptible to variations of the hydrodynamic regime. Thus, for the accurate determination of material flux it is essential to either simulate the external flow regime inside the chamber or to set specific flow patterns for experimental purposes. This is accomplished by a mesocosm system. The ambient water flow is detected by current meters. Their signal is transformed into a respective rotating speed of the mesocosm disc. This rotation in combination with an outward directed water flow through the center of this disc generates a homogeneous flow field above the sediment.

An injector allows the introduction of particles (e.g. algae for food pulse experiments) or solutes into the chamber. This injector was already successfully employed during food pulse studies 4850 m deep at the Porcupine Abyssal Plain.

Microsensors (O2 , H2S, pH) (Unisense, DK) and an oxygen optode (Aanderaa, NO) will monitor the water body overlying the sediment. Within the next months a profiling system with microsensors inside the chamber will be developed.

Figure 2: Time course of the oxygen concentration in a chamber equipped with a gas exchange system in comparison with a control chamber not fitted with a gas exchange system and the reservoir during two tests.

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Physical Properties of Hydrate Bearing Sediments Spangenberg E., Kulenkampff J. GeoForschungsZentrum, Department of Petrophysics and Geothermics, Telegrafenberg, F222, 14473 Potsdam, Germany, erik@gfz-potsdam.de, hannes@gfz-potsdam.de

Introduction In addition to seismic data, geophysical information from wireline logs can be valuable in the detection and evaluation of gas hydrate intervals. In the focus of interest are the sonic velocities and electric resistivities because they are more strongly effected by the presence of gas hydrate than other physical properties. For example downhole measurements of electrical resistivity and sonic velocity are used to derive gas hydrate saturations Sh based on Archie’s equation and Wyllie’s time average relation.

These are semi-empirical equations which relate the measured physical value to volumetric properties as porosity and water saturation SW. Not only the volumetric content but also the varying modes of the occurrence of this substance, e.g. disseminated as pore filling material, nodular, layered, or massive, strongly influences the physical sediment properties. The influence of disseminated, nodular, and layered gas hydrate on electric and seismic properties is studied. In some cases the results are significantly different from what the Archie equation with the standard cementation and saturation exponent and the time average relation would predict. However, up to now little is known about the physical properties of gas hydrate bearing sediments and more data from bore hole investigations and laboratory studies are urgently needed to get a better understanding of gas hydrate reservoirs, to improve the existing interpretation methods, and to develop new models.

Electrical Properties To determine the amount of hydrate in the pore space from in situ measurements of electrical properties different author suggest

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the use of Archie’s equation.

(1a) Sw: water saturation; φ: porosity; σw: conductivity of the pore filling brine; σ: conductivity of the rock; a,m,n: empirical parameters For practical applications equation (1a) is often used with the resistivity index RI,

(1b) which is the ratio of rock conductivities when the rock is fully and partially saturated.

Following this suggestion the fraction of the total pore space occupied by gas hydrates has been estimated from resistivity measurements in gas hydrate research wells (ODP Leg 164 site and Mallik 2L-38). The empirical saturation exponent in both studies was chosen to n=1.9386. Our theoretical investigations on the electrical properties of hydrate bearing loose sediments show that the Archie’s saturation exponent depends on the form of hydrate occurrence, the properties of the host sediment, and that the saturation exponent depends on saturation itself. If we take surface effects into account, we found for pore space hydrate that the saturation exponent depends also on grain size. The theoretical findings could be proved by experiments on glass bead samples (see. Figure 1).

Figure 1: Saturation exponent n as a function of water saturation from experiments with glass beads and modelling. The ratio r/L is the ratio of the grain size with the bound water layer (r ) and without the bound water layer (L). Assuming a constant bound water layer this ratio characterizes the grain size.

Elastic Properties To study the influence of hydrate on the elastic properties of loose sediments we used the same geometrical models as for the modelling of the electrical properties. The results show significant differences to the time-averagerelation and its derivates. The geometrical model we used for pore space hydrate is a cubic sphere pack. Taking into account that water is the wetting phase, the hydrate forms apart from the grains in the pore space and does not act as a grain cement. For hydrate saturations greater 15% the model predicts the formation of a hydrate skeleton within the pore space of the host sediment. The hydrate skeleton entraps the sand grains and produces a consolidated sediment. The transition from the unconsolidated to the consolidated state of the sediment does not result in a clear change in the dependence of seismic wave velocity on hydrate saturation . To prove the theoretically predicted transition from the unconsolidated state to the consolidated at hydrate saturations greater 15% we carried out an experiment with loose sand, water, and different THF-hydrate saturations. The experiment showed the transition in the predicted hydrate saturation range (see Figure 2).

Figure 2: Comparison between the time-average-relation, the timeaverage-relation adjusted for unconsolidated sediments, and our sphere pack model. The model predicted area of unconsolidated conditions is shown together with a photograph of sand samples with different THF-hydrate saturation.

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Imaging of the internal structure of fluid upflow zones with detailed digital Parasound echosounder surveys Spieß V., Zühlsdorff L., von Lom-Keil H., Schwenk T. Fachbereich Geowissenschaften, Universität Bremen, vspiess@uni-bremen.de

Sites of venting fluids both with continuous and episodic supply often reveal complex surface and internal structures, which are difficult to image and cause problems to transfer results from local sampling towards a structural reconstruction and a quantification of (average) flux rates. Detailed acoustic and seismic surveys would be required to retrieve this information, but also an appropriate environment, where fluid migration can be properly imaged from contrasts to unaffected areas. Hemipelagic sediments are most suitable, since typically reflectors are coherent and of low lateral amplitude variation and structures are continuous over distances much longer than the scale of fluid migration features.

During R/V Meteor Cruise M47/3 and R/V Sonne Cruise SO 149 detailed studies were carried out in the vicinity of potential fluid upflow zones in the Lower Congo Basin at 5°S in 3000 m water depth and at the Northern Cascadia Margin in 1000 m water depth.

Unexpected sampling of massive gas hydrates from the sea floor as well as of carbonate concretions, shell fragments and different liveforms indicated active fluid venting in typically hemipelagic realms.

The acoustic signature of such zones includes columnar blanking, pockmark depressions at the sea floor, association with small offset faults (< 1m). A dedicated survey with closely spaced grid lines was carried out to image the spatial structure of the upflow zones with the Parasound sediment echosounder (4 kHz), which data were digitally acquired with the ParaDigMA System for further processing and

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display. Due to the high data density, amplitudes and other acoustic properties could be investigated in a 3D volume and time slices as well as reflector surfaces were analyzed. Pronounced lateral variations of reflection amplitudes within a complex pattern indicate potential pathways for fluid/gas migration and occurrences of near-surface gas hydrate deposits, which may be used to trace detailed surface evidence from side scan sonar imaging down to depth and to support dedicated sampling.

Northern Cascadia Margin During R/V Sonne Cruise SO 149 (August 2000) a small scale seismoacoustic survey was carried out in the vicinity of recent gas hydrate findings on the sea floor. A dense grid of 2550 m line spacing was measured with digital sediment echosounder (Parasound/ ParaDigMA) and multi-channel seismics to reconstruct spatial patterns in potential fluid upflow zones.

Digital Parasound data are presented in traditional profiles and as time slices averaging amplitudes over a depth range of 5 meters.

Automatic algorithms were applied for despiking, navigation correction and smoothing.

First arrival automatic picks were used to produce a bathymetric chart for comparison with Hydrosweep swath bathymetry.

An elongated low reflectivity zone in contrast to higher reflective layered sediments of hemipelagic turbiditic origin could be traced to depth. Gas hydrates were found near locations of lower surface reflectivity indicating active methane release. At depth, spatial reflectivity patterns seem to indicate parallel bands of reflecitivity, which may belong to a complex

fault system, lacking, however, a clear surface expression.

Lower Congo Basin During R/V Meteor Cruise M47/3 sea floor depressions observed during previous GeoB research cruises to the area were investigated in some detail to search for active venting and asscociated phenomena. In two sea floor samples (gravity cores) gas hydrates were found and brought in large amounts up to the sea surface.

Bathymetric charting indicated several pockmarks with depressions on the order of 10-30 m and diameters of 500-2000 meters. Most of these were visited during the cruise and indication of active venting had been found. A fine scale morphology of single pockmarks could not be derived from swath sonar data due to high variability of sounding data, which may be attributed to the extremely soft sediment of high water content and low surface reflectivity.

Therefore digital Parasound data had been analyzed to precisely determine water depth through application of a first arrival pick algorithm including despiking, editing and smoothing steps as well as navigation processing. The result is a digital Parasound bathymetry. The morphology of the pockmark is clearly visible in greater detail revealing a depression deeper than 15 m and internal structuring.

In the vicinity of Site GeoB 6520, where gas hydrates had been collected from the sea floor and at ~4 m sub-bottom depth, high reflection amplitudes were observed. AT locations with low surface reflectivity, gas hydrates were absent, but indicators for fluid venting as mussles or carbonates were present. Hence, high amplitudes may be indicative for massive hydrates in high concentration, causing sufficient changes in acoustic impedance to increase reflection coefficients. Accordingly, we assume that also at depth high amplitudes may be related to gas hydrate accumulations, which in turn allows quantification of near-

surface hydrate from spatial Parasound surveys.

Results and Conclusions Digital echosounder data are suitable to produce through signal processing and automatic picking of first arrivals a high-resolution bathymetry. Data quality and accuracy is superiour to swath sounder bathymetry derived from currently installed systems on R/V Meteor and R/V Sonne, since only sea floor reflections are used lacking energy scattered over a longer time periods.

- Digital echosounder were used to generate a spatial image of fluid upflow zones including detailed variations in surface topography and reflectivity as well as internal amplitude distributions and identification of faults and columnar blanking zones.

- Amplitude maps in time slices allow to trace upflow zones, indicated by low amplitudes and absence of layering and related to complex structural patterns.

- At the Northern Cascadia Margin lateral amplitude variations seem to be controlled by structural disturbances (absence of layering) rather than impregnation by hydrates.

Columnar zones widen with depth and follow a planar surface - In the Lower Congo Basin high reflectivity zones were identified both in the vicinity of gas hydrate findings at the sea floor as well as near the assumed gas/fluid upflow, which indicates the presence of gas hydrates as the main cause for high reflection amplitudes. Due to the low wet bulk density, normal reflection coefficients are very low, and high amplitudes therefore may indicate the presence of elements of anomalous physical properties, mainly of higher velocity. High amplitudes found around a 'chimney' of low reflectivity may indicate the gas supply chimney, and hydrate growth zones at its rim.

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Formation Kinetics of Porous Gas Hydrates Staykova D.K. (1), Goreshnik E. (1), Salamatin A.N. (2), Kuhs W.F. (1) (1) GZG Abt. Kristallographie, Georg-August-Universität Göttingen, 37077 Göttingen, Germany (2) Dept. of Applied Mathematics, Kazan State University, Kazan 420008, Russia

Clathrate hydrates form when water molecules get into contact with gas molecules at the high pressure- low temperature conditions of stability of the hydrate phase. The understanding of the formation process is important for a number of cases in geology and chemical engineering. Unfortunately, our present understanding of the physico-chemical processes controlling the formation and decomposition kinetics is rather poor. We present here results of in situ diffraction experiments focused on the formation of CH4 and CO2 gas hydrates at variable pressure and temperature. The rates of transformation of spherical grains (Fig. 1a) of deuterated ice Ih to gas hydrate were measured using neutron and X-ray time-resolved powder diffraction at the high-flux diffractometer D20 at ILL, Grenoble and the high-energy synchrotron beamline BW5 at HASYLAB, Hamburg respectively. A number of reactions were followed over a period of 10 to 20 h.

Data were analysed in an automated way using the Rietveled refinement program GSAS. Quantitative information on the amount of the formed gas hydrate was obtained as a function of time. A comparison of the results from the different formation runs leads to the following conclusions: - All reactions showed an initial fast and nonlinear development followed by a slower linear behaviour with time.

- The pressure dependence of the rate of iceto-methane hydrate transformation was found to be different at T=272.15K and at low temperature T=230K. - A clear difference between carbon dioxide and methane in the gas-hydrate formation kinetics was established. The reaction of CO2 was distinctly faster than for CH4 at similar excess of fugacity (f-f0)/f0 (f0 -‚fugaci-

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ty at the decomposition pressure). A maximum conversion of ice Ih to type I gas hydrate of 22% and 56% was obtained for CH4 and CO2 respectively. It seems probable that this observation is connected to the smaller pores sizes observed in CO2 hydrates (Kuhs et al. 2000) but we have no detailed understanding of the molecular processes involved at present.

- CO2 hydrate forms a transient type II crystal structure in coexistence with the usual type I hydrate reaching a maximum of 5% of total volume after 5h of reaction. The initial growth is rapid and appears to be preferred over a type I hydrate. This may indicate that it is somewhat easier to form the small cages of a hydrate structure (which are more numerous in a type II hydrate) in agreement with suggestions by Sloan and Fleyfel (1991) and experimental evidence obtained by Pietrass et al (1995). The subsequent re-growth of the type II hydrate into the thermodynamically more stable type I hydrate appears to be a very slow process.

The data were further analysed using a phenomenological mathematical model (Salamatin & Kuhs, 2002). It is based on the electron microscopic evidence for a submicron porous microstructure of gas hydrates as observed by Kuhs et al. (2000). The model describes the principal stages and rate-limiting processes that control the kinetics of the porous gas hydrate crystal growth from ice powders. It separates three stages of which the first two could be observed in our experiments. The model assumes an initial stage of hydrate film spreading over the ice surface and a second stage, limited by the clathration reaction at the ice-hydrate interface (and not by the gas transport to the ice/hydrate interface via the

sub-micron pores). This later stage prevails after the ice grain coating. Our electron microscopic pictures from a forming methane hydrate (Fig.1b) show that after 5h the ice surface is not fully covered with porous hydrate.

The model assumes that initially the hydrate formation from the ice powder is controlled by wS, the rate of the clathrate film spreading over the ice surface directly exposed to the ambient gas phase. The total degree of the transformation a develops with time as given in equation (1):

only a lower bound as the measurements at higher temperature may be affected by a partial ice recrystallisation during the ongoing clathration reaction with some fusing of adjacent grains, a process for which we can find some evidence in our electron microscopic observations. A full version of the paper will be presented at the ICGH-2002 meeting in Yokohama (Staykova at al., 2002)

(1)

where t is the time. A, B are functions of ice grain and initial hydrate film parameters and could be regarded as constants. The parameter wS can be determined from eq. (1) when it is applied as a fitting function f(t) to the experimental data of the hydrate mole fraction (Fig.2a).

The data treatment showed no appreciable difference in wS for the different kinetic runs; in all cases the obtained value is around 0.014 min– 1. This could suggest that the pressure and temperature conditions in the system do play only a minor role in the coating process.

The model assumes that after the end of the ice grain coverage with a hydrate shell the dominating rate-limiting process is the reaction on the ice/hydrate interface. Equation (2) is valid for this stage:

Figure 1: FE-SEM pictures of (a) the ice spheres used as starting material and (b) an ice grain after a 5 h reaction with CH4 gas at 60 bar and –1 °C showing a partial coverage with porous gas hydrate.

(2) It can be used to obtain parameters A and B from a linear fit (Fig. 2b) of each data plot (1-α)1/3 = f(t>400min) in the time region of validity of (2). Our data analysis gave us an estimation of 5.8 kcal/mol for the activation energy necessary for the clathrate formation reaction after the end of hydrate film covering process of the ice surface. As this second stage of the reaction is not well developed at lower temperatures due to the time limitations of our first runs, this number must be considered as preliminary and indicative only. It is most likely

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Sloan, E.D. & Fleyfel, F. (1991). A molecular mechanism for gas hydrate nucleation from ice. American Institute of Chemical Engineering Journal, 37, 1281-1292.

Staykova, D.K., Hansen, Th. , Salamatin, A. N. & Kuhs, W.F. (2002). Kinetic diffraction experiments on the formation of porous gas-hydrates. Proceedings of the 4th International Conference on Gas Hydrates, Yokohama, Japan.

Figure 2: Results from a fit of data (a) of the methane hydrate formation reaction at P = 60 bar, T = 268 K with equation (1) of ice coverage stage and linear fits (b) of the second stage data obtained for a reaction of CH4 hydrate at P = 60 bar and temperatures 230 and 268 K.

References Kuhs, W.F., Klapproth, A., Gotthardt, F., Techmer, K. & Heinrichs, T. (2000). The formation of meso- and macroporous gas hydrates.

Geophysical Research Letters 27 (18), 29292932.

Pietrass, T., Gaede, H.C., Bifone, A., Pines A., and Ripmeester, J.A. (1995). Monitoring Xenon Clathrate Hydrate Formation on Ice Surfaces with Optically Enhanced 129Xe NMR. Journal of American Chemical Society, 117, 7520-7525.

Salamatin, A. N. & Kuhs W.F. (2002).

Formation of Porous Gas Hydrates.

Proceedings of the 4th International Conference on Gas Hydrates, Yokohama, Japan.

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Experimental and theoretical concepts to quantify deep-sea environments in an Autoclaved Experimental Chamber (AEC) Steffen H., Gust G. Ocean Engineering 1, Technical University Hamburg-Harburg, 22305 Hamburg, Germany

The design of the autoclaved experimental chamber (AEC) of the BMBF gas hydrate research project OMEGA SP5 has been completed and the system is under construction. AEC is a mobile, compact experimental system suitable for on- and offshore as well as ship operations to investigate natural and artificial gas hydrate/sediment samples under a wide range of chemical, thermodynamic, hydrodynamic and biological aspects. Cores are introduced decompression-free from a transfer chamber via an adapter/pressure lock.

The essential elements of the AEC, being the pressure vessel (working pressure: up to 55 MPa, interior dimensions: Ă&#x2DC;300x1400 mm, weight: 1.5 to, volume: 99 l) and the pressure adapter/lock with all peripheral components are integrated into a seaworthy, certified 20ft-container.

To couple the autoclave coring unit carrying decompression-free sediment samples as part of the laboratory transfer chamber (LTC, OMEGA SP1 of TU Berlin) to the AEC necessitated special modifications to the laboratory container such as integration of a crane and a hatch. Sediment cores (Ă&#x2DC;100x700 mm) are transferred from the LTC into the AEC without loss of the original in-situ pressure and temperature conditions (within acceptable error mar-gins). LTC transfer chamber and AEC are coupled via an adapter/lock-chamber which removes (under pressure) the seal at the bottom of the LTC and guides the sediment core through an opened port into the AEC. Upon completion of the transfer, the sediment core is exposed in the AEC to an adjustable, controlled deep-sea environment representing

the in-situ conditions or conditions selected by the user as to pressure, temperature, chemical surrounding and boundary layer hydrodynamics.

In addition to optical surveillance via pressure proof spy glasses and TV, a wealth of investigations are performed using sensors and different sub-sampling devices mounted within the pressurized volume. The handling of the sediment core (rotation and axial movement) and of all other kinetic tasks in the interior is carried out by mechanic, hydraulic and electric interfaces to the outside. Pressurized water and/or gas of defined conditions from a 40-l reservoir is used for establishing settings which represent boundary layer flow with fluid movement through the core; a simulation of deep-sea sediments with and without gas hydrates and venting fluids. By measurement of the associated pressure differences, the z-component of the resistance-tensor may thus be determined. An alternative use of the reservoir is to provide a controlled source-sink feed through system for the fluid. Core exposure is not only feasible for natural sediment samples under defined thermodynamic/hydrodynamic/biogeochemical conditions, but also for artificial hydrate-containing samples generated inside the AEC and subsequently destabilized. Investigations of destabilization with such a â&#x20AC;&#x2DC;standardised hydrate core' permit to determine quantitatively the influence of environmental parameters such as pressure, temperature, chemical constituents and hydrodynamics with high repeatability and accuracy for subsequent experiments with natural samples. Exposure of

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the core (both surface and pore space) to almost natural hydrodynamics is an important and unique feature of the AEC concept. It is implemented by a technology developed and patented by the MT1/TUHH research group. A numerical evaluation of the interfacial bottom stress for various operational conditions is under way, together with comparisons with existing experimental data and an alternative analytical assessment. This aspect is of particular importance, since we postulate the following working hypothesis concerning the influence of hydrodynamics on the destabilization of natural marine gas hydrates: - The shear generated by the movement of water near the bed enlarges the effective surface with active methane diffusion and consequently increases the destabilization rate.

- Stronger turbulent boundary-layer flows increase the vertical flux of methane and consequently the destabilization rate.

- Increasing bottom stress enhances the destabilization rate through removal of microscopically sized, intact hydrate cage segments.

These hypothesis will be verified or falsified in upcoming experiments in the AEC. It is expected that from the experiments under preparation for the AEC both answers and new questions on the role of gas hydrates in the geosystem will arise. The presentation provides selected aspects of final design solutions, a video of the ongoing containerAEC system integration, and numerical results of the hydrodynamics established in the AEC.

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NATLAB: Seismic Parameters and Physical Properties of Marine Sediments Theilen Fr., Klein G., Thießen O., Schmidt M., Bohlen T. Institut für Geowissenschaften der Christian-Albrechts-Universität zu Kiel

Introduction The main objective of the NATLAB-project is focussed on the assessment of shear waves in the sea floor under in-situ conditions and the correlation of shear wave velocities with sediment properties. The dynamic shear moduli are very sensitive parameters with respect to shear strength and the stiffness of sediments, so that they allow an easy access to sea floor stability and offshore engineering problems.

The shear wave velocities are obtained using dispersion analysis of Scholte waves, which are also observable in the lower part of the water column and thus assessable by a continuously towed streamer just above the sea floor. This method promises a higher efficiency for the investigation of sea areas in comparison with ocean-bottom-seismometers. Furthermore, seismic parameters such as seismic reflectivity of gas containing layers and seismic velocities are evaluated for comparison with physical sediment properties investigated with geological and geochemical methods on core samples.

Three cruises have been performed in 2001 on RV ”Poseidon” and RV ”Alkor” in the Arkona Basin and Kiel Bay for the acquisition of the geophysical and geological data.

Results from Sea Experiments Sediment properties in the Arkona Basin During the cruise no. 266 of RV “POSEIDON” 7 cores were recovered in the Kiel Bay area and in the Arkona Basin. The maximum core gain was 11,2 m. Recent and subrecent green muddy sediments (recent to litorina-age), postglacial gray clay and silt and late glacial reddish silty clays were sampled in the Arkona Basin. Sediments are characterized by different

gas contents indicated by zones with "seismic turbidity" or with clear structured seismic reflectors. The sedimentation boundaries detected in the cores could well be correlated with the seismic reflectors.

Directly after the end of the cruise, selected sections of the cores were investigated in the core logger of the GEOMAR Institute for Marine Research with respect to the magnetic susceptibility, bulk density, and compressional (P-) wave velocity. The P-wave velocities showed reduced values of about 1150 m/s in the recent near surface layers, whereas unconsolidated water saturated sediments are characterized by values of 1450-1480 m/s. The velocity increases to 1400 m/s in the transition zone from subrecent muddy sediments to subglacial clays which show values of up to 1550 m/s (Fig. 1). The shear strength, measured with a mechanical probe, increases with depth from 0,4 kg/cm2 up to about 1.5 kg/cm2.

In the deeper sediment sections these values vary between 0,8 g/cm2 and 1,6 g/cm2 and amount up to 2,4 kg/cm2 in silt enriched layers.

The bulk density increases in the same way from 1,2 g/cm3 to 1,8 g/cm3.

Geochemical investigations have been performed on various cores sampled in the Arkona Basin.

Sediment and pore water will be sedimentologically and geochemically characterized. Beside grain size measurements, density determination, organic and inorganic carbon content measurements the determination of the gas content and composition in the sediments is a major goal of the investigations. The mean concentration of gas from pore water which is an important parameter for modelling the P-wave velocity structure, was about 150 ml/l.

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Figure1: Results of the analysis of core Po266-SL07 in the central Arkona Basin.

Note the low P-velocity in the near surface due to high gas content.

Figure 2: a) Reflection seismic section from the south east rim of the Arkona Basin, Baltic Sea. The section shows the firstchannel at about 30m distance from the 0.1 l airgun, both at 5 m tow depth. Refracted first arrival occur due to the shallow water depth, dominantly nearby the location marked by the arrow. b) The p-f-domain spectra of a shot section near shot no. 9700 reveals the dispersive mode with phase slowness corresponding to 400-800 m/s. c) Forward modeling of a model derived from the reflection seismics and initial guesses for shear wave velocities.

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Nitrogen, methane and carbon dioxide were found to be the main components. Hydrogen sulfide was proven as well as trace component in near surface layers. Moreover, gases (hydrocarbons) adsorbed on grain surfaces from grain size fraction <63_m has been measured. Gas saturation conditions are calculated for the various cores and sedimentological and geochemical data will be used for further seismic modelling.

Another important feature was observed in single channel high frequency reflection seismic sections acquired with a boomer. The spectra of this source covers mainly a frequency range of about 800 â&#x20AC;&#x201C; 2600 Hz, which are normally observed on reflectors in gas free sediments. The reflections from gas-containing layers are characterized by broad spectra covering a frequency range of up to 6500 Hz. The high frequencies are obviously caused by backscattering from the gas bubbles in the subsurface. It can be assumed that size of the bubbles and free gas content in the sediments correlate with the seismic spectra. This effect is strongly dependent on frequency. Frequencies lower than 500 Hz produce a strong reflection with inversed wavelet resulting in a negative reflection coefficient. This observation gave rise to the idea to perform modelling calculations in order to get information on quantitative relationships between the gas content and the reflectivity patterns. This is probably an important tool for the evaluation of BSRâ&#x20AC;&#x2122;s.

Scholte boundary wave experiments with a deep towed reflection seismic system in the Arkona Basin The geophysical investigations focus on the evaluation of the seismic data and test measurements on Scholte waves at selected sites of the Arkona Basin. A reflection single channel seismic section of the area where dispersive interface waves such as Scholte waves have been recorded is shown in Fig. 2a.

It is characterized by a weak sea floor reflection underlain by a series of stronger horizons dipping slightly to the east. Especially

the strong reflector at 0.11 s TWT in the range of shot no. 9700 is remarcable, since it seems to strongly affect the generation of the dispersive interface waves. This section yields the basic subsurface structure for the derivation of a start model to calculate the theoretical dispersion spectra as shown in Fig. 2c in the frequency range between 2 and 20 Hz. The Scholte wave experiments have been performed on this profile using airguns with volumes of 2,5 l and 1,2 l and a 200 m long streamer, both towed about 8 - 10 m above the sea floor. The corresponding dispersion spectrum is shown in Fig. 2b. Note, that the dispersion mode is resolved within the frequency of 5 to 12 Hz, but resolution is poor otherwise. The inversion of the dispersion curves with respect to shear wave velocities as a function of depth by fitting the dispersion curves requires the identification of the order of the mode and is ambiguous in case of strong band limitation. Inversion methods which include information from the amplitude distribution of the spectra may help to reduce the ambiguity. Therefore forward modelling under consideration of the geological structure and the P-wave velocity structure derived from reflection seismic sections as shown in Fig. 2a was used to produce an estimate of a velocity model such as shown in Fig. 2c.

In general, the experiments have shown, that it is possible to acquire dispersive interface waves which reveal information on the shear wave velocity of the subsurface with a deep towed reflection seismic system. However, the frequency band showing clearly visible dispersion curves is very limited, which implies that the use of a more sophisticated inversion method including information on the amplitude distribution in the f-p spectra is favourable.

This method has yet to be adapted for the prevailing marine environments.

The Scholte wave experiments show clearly, that the seismic sources should be operated near the sea floor. Furthermore, experiments with ocean bottom seismometers showed that

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Scholte waves are very slow in muddy sediments so that a special data acquisition geometry is required allowing close shot and receiver distances.

Ackowledgements This project is funded by the BMBF under contract number 03G0564D. Thanks are also due to the captains and crews of of RV “Poseidon” and RV “Alkor” for their excellent cooperation.

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Anaerobic oxidation of methane above gas hydrates Treude T. (1), Boetius A. (1, 2), Knittel K. (1), Rickert D. (3) (1) Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany, Phone: ++49 421 2028 648, Fax: ++49 421 2028 690, Email: ttreude@mpi-bremen.de (2) Alfred Wegener Institute for Polar and Marine Research, 27515 Bremerhaven, Germany (3) GEOMAR Research Center for Marine Geosciences, 24148 Kiel, Germany

Introduction Aim of this study was to investigate rates of anaerobic oxidation of methane (AOM) and sulphate reduction (SR) in methane-rich surface sediments at Hydrate Ridge (Cascadian Margin, off Oregon). At this site methane is oxidized with sulphate by a consortium of methane-oxidizing archea and sulphate reducing bacteria (Boetius et al., 2000) via the following net equation:

Sites with distinct microbial mats (Beggiatoa) and clams (Calyptogena) were sampled to investigate the coupling of sulphate and methane cycles. The presence of Beggiatoa and Calyptogena indicates a high production of hydrogen sulphide in the surface sediment as these organisms use sulphide as an energy source. The production of sulphide at Hydrate Ridge is directly coupled with SR and therefore possibly as well with AOM. Close-by sites without Beggiatoa or Calyptogena covering were sampled to obtain reference data.

Materials and Methods Samples were obtained by a video-guided multicorer. Radioactive tracers of methane (14CH4) and sulphate (35SO4) were injected separately into subcores and incubated for 24 h at in situ temperature to measure AOM and SR. After incubation, the upper 10 cm of the sediment cores were split into 1 cm intervals and fixed to stop the microbial activity. In the home laboratory the ratio of 35S-sulphate to formed 35 S-hydrogen sulphide and of 14C-methane to

formed 14C-carbon dioxide respectively was measured.

Results and Discussion The rates of AOM measured at Hydrate Ridge are some of the highest ever found in cold marine sediments (Fig.1). At the Calyptogenasite the rates reached up to 2.7 Âľmol/ccm/d in single samples. Integrated over 0-10 cm sediment depth, the rates were highest at the Calyptogena-site (49.8 mmol/m2/d) followed by the Beggiatoa-site (4.3 mmol/m2/d). Lowest rates (1.1 mmol/m2/d) were measured at the Reference site. A close to 1:1 stoichiometry of AOM and SR (as claimed in eqn 1) was found at the Calyptogena-site. At the Beggiatoa-site AOM was about one order of magnitude lower compared to SR, indicating that sulphate reducers in the depth of AOM activity used also other electron donors than methane.

AOM and SR followed the same pattern at both high-sulphidic sites with subsurface peaks between 4 and 6 cm sediment depth. In correspondence, sulphate is rapidly depleted in the depth of high SR activity. At the Reference site methane oxidation and SR were not coupled. Methane oxidation was highest at the sediment surface, indicating that the process might be aerobic. The SR profile is more typical for organic rich sediments with increasing activity beneath the oxic layer.

Counts of consortium aggregates by fluorescence microscopy revealed highest numbers (up to 1.5^108/ccm) at the sulphidic sites compared to rather low numbers (0.2^108/ccm) at the Reference site. At the Beggiatoa-site highest aggregate abundance (1.3^108/ccm)

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was found in the depth of the AOM and SR peak.

Figure 1: AOM, SR and sulphate in three types of surface sediments at Hydrate Ridge.

References Boetius, A., Ravenschlag, K., Schubert, C.J., Rickert, D., Widdel, F., Giesecke, A., Amann, R., Joergensen, B.B., Witte, U., Pfannkuche, O. (2000). A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623-626.

Acknowledgments The fieldwork was done during Sonne expedition SO 148-2, which was performed as part of the BMBF program TECFLUX. Laboratory studies were performed within the Geotechnologien program MUMM.

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INGGAS-Flux: New tools for energy and fluidflux: pore pressure and thermal gradient probes Villinger H., Gennerich H.-H., Grevemeyer I., Kaul N. Fachbereich Geowissenschaften, Universität Bremen, Postfach 330 440, 28213 Bremen, Germany

Two different tools are designed and tested within this INGGAS subproject: 1. a 6m long heat flow probe to expand measurement capabilities from deep sea environments to shallow water (continental margins) in order measure reliable sediment temperature gradients in the presence of bottom water temperature variations 2. a pore pressure tool to measure in situ pore pressures in sediments in order to quantify fluid flow. This second tool is split into two units: a) the data acquisition unit and b) an autonomously operating data transmission buoy.

1 Heat flow probe The new heat probe is capable to measure temperature gradients and in situ thermal conductivity in sediments to determine terrestrial heat

flow. The large penetration depth of 6m, twice as deep as normally used instruments is necessary to get reliable results in water depth of less than 2000m where varying bottom water temperatures create transient temperature disturbances in the subsurface. This is very often the case for heat flow surveys over gas-hydrate bearing sediments at continental margins. The mechanical design of the probe follows the violin bow concept and is adapted in size and material strength to the desired maximum penetration depth. Numerical modeling of the dimensions of sensor string and strength member assisted in the final design. The data acquisition in the instrument is normally under realtime control from a deck unit on board the research vessel but can also be operated in a completely autonomous way if no suitable cable is available on board.

Data acquisition unit (in heat probe at seafloor)

Data logger for • Signal conditioning of analogue temperature signal • A/D conversion with 22 bit resolution • Data storage • Control of heat pulse for in situ thermal conductivity measurement • Data acquisition and storage of penetration monitoring sensors (pressure, tilt, acceleration, altimeter) • Real-time communication with deck unit through coax deep sea cable • Temperature range of –2 to 70 °C • Temperature resolution of < 1mK from –2 ° to 12 °C • Battery and storage capacity allow continuous operation for 3 days • Operational up to 6 km water depth

Deck unit (on board research vessel)

PC for: • Data capture and storage on hard disk • Control of the instrument at the seafloor • Communication with the instrument at the seafloor through coax deep sea cable • Real-time graphical display of data

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The data acquisition system including the communication package is designed and built by an industry partner according to our specifications. The complete mechanical system is shown in Figure 1. A first sea trial will take place during M54/2 off Costa Rica in August/September 2002.

2 Pore pressure tool The goal is to detect vertical fluid flow within seafloor sediments with rates as low as 1 mm/a. This will be achieved by measuring pore pressures in the sediments at various depths for a maximum period of two month with a minimal time resolution of 10 minutes to monitor tidal and other low frequency effects.

We decided to employ one differential pressure transducer and three subsurface pressure ports using a hydaulic multiplexer. Operation of the hydraulic multiplexer has been tested in the laboratory and under deep ocean pressure condition in a pressure chamber as well. After free-falling to the seafloor the instrument records pressures over a preset time window and the data are transfered to the satellite communication unit. This unit will surface after the end of the measurement period and send the data to shore via an IRIDIUM satellite link.

The complete system is designed as expendable system to save additional ship time cost for recovery of the data. A sketch of the system design is shown in Figure 2.

Data acquisition unit (pore pressure measurement)

Data logger for • Signal conditioning of analogue differential pressure signal • A/D conversion with 22 bit resolution • Data storage • Data acquisition and storage of environmental parameters (tilt, temperature) • Data transmission to satellite communication unit • Battery and storage capacity allow continuous operation for 2 months • Operational up to 6 km water depth

Satellite communication unit

• • • •

Storage of pressure and environmental data Timing release Data compression Transmission of complete data set through IRIDIUM satellite link

The satellite communication system is designed and built by an industry partner according to our specifications. The complete mechanical system is shown in Figure 2. A first sea trial will take place at the end of March 2002 in the Baltic Sea. A second test is scheduled for October 2002.

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Figure 1: New heat probe with total length of 8,1 m and a minimum total weight of ca. 900kg.

Figure 2: Sketch of the expendable differential pore pressure probe. The data transmission unit is a self-contained satellite data transmission link.

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Fluid-geochemistry of active mud volcanoes in the Black Sea (OMEGA) Wallmann K., Bohrmann G., Drews M., Suess E. GEOMAR Research Center for Marine Geosciences, Wischhofstrasse 1-3, 24148 Kiel, Germany

During cruise M52-1, sediment cores were taken from the active Dvurechenskii mud volcano situated in the Sorokin Trough, Black Sea. Recovered sediments contained finely dispersed gas hydrates and fluids with an unusual composition. Thus, the dissolved chloride concentration increased to 850 mM, a value twice as high as the average chloride content of Black Sea bottom waters. This strong chloride enrichment could be caused by the dissolution of evaporite rocks, by formation of gas hydrates, by phase separation at high temperatures (>350 °C) or might point to the presence of ancient formation waters formed via evaporation of seawater.

Surprisingly, the δ18O values of the recovered brines (-2‰ SMOW) were very close to ambient bottom waters so that hydrate formation and seawater evaporation could be discounted as sole mechanisms of fluid formation. In contrast, both evaporite dissolution and phase separation at high-temperatures might enhance the chloride content of fluids without affecting the isotopic composition.

Currently, the fluids are further analyzed to decipher the possible formation mechanisms.

Initial results indicate very high dissolved Ba, B and Li concentrations and low Mg values. This chemical signature suggests very high temperatures in the source region and might therefore confirm the occurrence of phase separation at depth. If true, the studied mud volcano would be associated with hydrothermal processes which are usually driven by magmatic processes. Further in depth studies are needed to confirm or discount this proposition.

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Mallik 2002: An In-situ Gas Hydrate Laboratory Weber M.H. and the Mallik working group GeoForschungsZentrum Potsdam, AB2, Telegrafenberg, 14473 Potsdam, Germany

From December 2001 to March 2002 fieldwork was conducted on a new gas hydrate research well program at the northeastern edge of the Mackenzie Delta, Northwest Territories, Canada (Fig. 1 top). The Mallik research well program of 2001/2002 includes the drilling of a 1200 m deep main production research well (Mallik 3L-38) and, for the first time, two 1150 m deep scientific observation wells offset 40 m from the main well (Fig.) for geophysical monitoring of the main well. The science and engineering research objectives for the production research well focus on the assessment of the production properties of gas hydrates, and the determination of the stability of continental gas hydrates.

After a long review process the drill site near Imperial Oil Mallik L-38, an industry exploration well drilled in 1972 (Bily and Dick 1974), was selected for the location of the gas hydrate research well program. This site located at the edge of the Mackenzie Delta, in Canadaâ&#x20AC;&#x2122;s Arctic was chosen as it offered favorable logistics and has the thickest known gas hydrate occurrences in the region. Detailed geologic, geophysical and engineering data were available from the original industry well and from a Mallik 2L-38 (Fig.) a research well program conducted in 1998 (Dallimore et al. 1999).

Well log interpretations and core samples from the 1998 research well revealed a strong lithological control on gas hydrate occurrences at Mallik. For the most part, gas hydrate occurred within coarse-grained sandy sediments that were typically interbedded with non-gashydrate-bearing, or very low gas hydrate content, fine-grained silty sediments. On the basis of the well log interpretations, more than 110 m of well defined gas-hydrate-bearing sands and silty sands were found between 897 and 1110 m (Collett et al. 1999). Quantitative

well-log-derived estimates suggest that in situ gas hydrate concentrations are very high with greater than 60% pore saturation throughout most gas hydrate layers, and in many cases more than 80% pore saturation. Within the cored interval from 886 to 952 m, visible forms of gas hydrate occurred as pore fillings and coatings on grain surfaces. In some sands and pebbly sands there were thin veins <1 mm thick and nodule-like gas hydrate up to 1 cm in diameter. In at least one interval of sandy conglomerate the gas hydrate actually formed a matrix, which supported the pebble clasts.

A wide ranging research program is being conducted at Mallik 3L-38 with extensive research in geophysics, core studies and the application of several new technologies to monitor in situ formation conditions. Full-scale field experiments, which for the first time also use two additional observation wells, monitored the physical behavior of the gas hydrate deposits and enclosing sediments to depressurization and thermal production stimulation. A substantially expanded science program for this research well program has been enabled through the acceptance of a research proposal submitted by the authors of this article as an International Scientific Continental Drilling Program (ICDP) project and it involves over 100 researchers from more than 30 research institutes.

The project leaders are the Japan National Oil Corporation (JNOC), the GeoForschungsZentrum Potsdam, Germany (GFZ), the Geological Survey of Canada (GSC), the United States Geological Survey (USGS), the United States Department of the Energy (USDOE), the India Ministry of Petroleum and the Natural Gas (MOPNG)1 and the Chevron-BP- Burlington joint venture group1. On behalf of the project

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leaders, Japex Canada Ltd. coordinates drilling operations and the Geological Survey of Canada coordinate scientific studies.

For further information see: http://www.gashydrate.com and http://icdp.gfz-potsdam.de.

References Bily, C., and Dick, J. W. L., 1974: Natural occurring gas hydrates in the Mackenzie Delta, Northwest Territories; Bulletin of Canadian Petroleum Geology, v. 22, no. 3, p.

340-352.

Collett, T. S., Lewis, R., Dallimore, S. R., Lee, M. W., Mroz, T. H., and Uchida, T., 1999: Detailed evaluation of gas hydrate reservoir properties using JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well down hole well-log displays; in Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate Research Well, Mackenzie Delta, Northwest Territories, Canada, (ed.) S. R. Dallimore, T. Uchida, and T. S. Collett; Geological Survey of Canada, Bulletin 544.

Dallimore, S.R., Uchida, T., and Collett, T.S., eds., 1999, Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate Research Well, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada Bulletin 544, 403 p.

Figure 1: Top - Location map showing site of the Mallik gas hydrate research well program, the winter ice roads and the drill roads.

Bottom - Detailed site layout showing surface conditions and locations for main well (Mallik 3L-38) and the two scientific observation wells.

1

Partnership under negotiation

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Real-time mud gas monitoring at Mallik 4L-38 and 5L-38 wells Wiersberg T., Zimmer M., Schicks J., Dahms E., Erzinger J., and the Mallik working group GeoForschungsZentrum Potsdam, AB 4, Telegrafenberg, 14473 Potsdam, Germany

In order to investigate the composition and depth distribution of gases occuring in the permafrost sedimentary setting of Mallik, we have analyzed in real time the mud gas during drilling of the research wells Mallik 4L-38 and 5L-38 as well as the gas liberated during a thermal production test. Gases dissolved in the drill mud were extracted using a gas separator which was installed at the mud pipe outlet (Fig. 1). The liberated gas was led through a heated teflon tube (~ 25 m) into a laboratory trailor. The gas was analysed for N2, O2, Ar, He, CO2, H2 and CH4 with a quadrupole mass spectrometer, for 222Rn activity with an alpha-spectrometer and for hydrocarbons (C1-C4) with a gas chromatograph. Gas and drilled solid hydrate samples were taken routinely for further detailed investigations in the GFZ laboratories.

The depth distribution of gases was similar in both wells. High methane concentrations in the drill mud were found in shallow layers of the permafrost (106 m), at the bottom of the

permafrost (650 m), between permafrost and gas hydrate bearing zone (770 m, 840 m) and in gas hydrate layers (890 m - 1100 m). Most layers can also be distinguished by their helium and radon concentrations and the C1/(C2+C3) ratio.

A key question is whether the sedimentary section penetrated had the potential to generate the observed gas occurrence in situ, or whether the gases migrated to their present location from deeper sources. Biogenic and thermogenic hydrocarbons differ in their C1/(C2+C3) ratios about several orders of magnitude, which helps to clarify the origin of the hydrocarbons.

In addition to the results of the mud gas monitoring, isotopic investigations will give further indications about origin and genesis of the gas. In the future we plan to study the noble gas and stable isotopes composition of gas samples as well as the composition and thermodynamic properties of gashydrate bearing sediments.

Figure 1: Experimental set-up

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Multi-Frequency Seismic Data in the Vicinity of a Gas Hydrate Site at the Northern Cascadia Accretionary Prism Zühlsdorff L. (1), Spieß V. (1), Schwenk T. (1), Chapman N.R. (2), Riedel M. (2), Hyndman R.D. (2, 3) (1) Dept. of Geosciences, University of Bremen, P. O. Box 330440, 28334 Bremen, Germany (2) University of Victoria, School of Earth and Ocean Sciences, P. O. Box 3055, Victoria, BC, Canada (3) Geological Survey of Canada, Pacific Geoscience Centre, P. O. Box 6000, Sidney, BC, Canada

During two research cruises of the German R/V Sonne in 1996 and 2000 (Cruises SO 111 and SO 149 – ImageFlux), a dense grid of high resolution multi-channel seismic and hydroacoustic lines was collected at the northern Cascadia margin close to ODP Leg 146 Sites 889 and 890. Detailed images of seafloor bathymetry provide information about sediment distribution, mass flow, and the effects of regional tectonics (Fig. 1).

Echosounder (Parasound) and 3D multichannel seismic data are combined with supplementary single channel seismic and deep-tow seismic data collected during two Canadian cruises on R/V J. P. Tully (1997/1999).

All data sets show a number of narrow, vertical blank zones and are compared near coring sites, where massive gas hydrates were sampled (Blank Zone 1, Fig. 2). If details like diffraction and high amplitude rims at the edges of the blank zones as well as the completeness of blanking are considered, the seismic signatures of both depositional structures and gas hydrates at or close to the seafloor are different for the different seismic systems, depending on source type, frequency range, and lateral and vertical resolution.

Assuming that active fluid transport is required to form gas hydrate, which is often indicated by the presence of a bottom-simulating reflector (BSR) in seismic data, mapping of BSR topography and BSR distribution on the basis of SO 111 seismic data reveals information about the regional distribution of permeability.

Since a clear BSR is present, diffuse fluid

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migration is inferred for the pervasively fractured sediments of the accretionary wedge.

In contrast, low-permeable bedded deposits appear to inhibit vertical flow and a BSR may only form below bedded deposits or in the vicinity of faults, where gas is locally provided at sufficient rates. An elevation of the BSR is interpreted as a local disturbance of the thermal gradient, which is related to an increase in hydraulic conductivity within tectonically deformed sediments and a subsequent guided rise of warm fluids. Thus, the generally diffuse seepage of fluids within the study area is superimposed by events of confined fluid release.

Since massive gas hydrate was sampled at Blank Zone 1, fluid flow at this site also appears focused rather than diffuse, assuming that the presence of gas hydrate is coupled to vertical fluid flow. If the seismic blanking within Blank Zone 1 is related to the presence of gas hydrate or free gas, then there is no significant transition zone between the blank zone and hydrate or gas free sediments.

However, although hydrate was sampled, it is still difficult to conclude which kind of seismic signatures are to be expected from massive gas hydrate or sediments hosting gas hydrate. It is expected that combining echosounder, swathsounder, and seismic data sets for a joint analysis and interpretation will provide a unique opportunity to understand hydrate forming processes as well as the required depositional and tectonic framework in greater detail.

Figure 1: 3D image of ImageFlux swatch sounder data (Hydrosweep)

Figure 2: Comparison of ImageFlux data (Parasound, water gun, GI-Gun#2) and R/V J.P. Tully data (DTAGS, airgun). Massive gas hydrate was sampled at Blank Zone 1. a) stacked SCS airgun data, b) stacked MCS GI-Gun data, c) migrated MCS GI-Gun data, d) stacked DTAGS deep-tow data, e) stacked MCS water gun data, and f) Parasound narrow beam echosounding data.

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Index

A Abegg, F. . . . . . . . . . . . . . . . . 8, 21, 23 Aloisi, G.. . . . . . . . . . . . . . . . . . . 21, 33 Amann, H. . . . . . . . . . . . . . . . . . . . . . 9 Amann, R. . . . . . . . . . . . . . . 19, 67, 79 Andreassen, K. . . . . . . . . . . . . . . . . . 29 Artemov, Y.. . . . . . . . . . . . . . . . . 21, 83 B Bauer, K. . . . . . . . . . . . . . . . . . . . . . . 11 Baumert, J. . . . . . . . . . . . . . . . . . . . . 14 Becker, H.J. . . . . . . . . . . . . . . . . . . . . 46 Beer, D. de . . . . . . . . . . . . . . . . 19, 111 Behain, D. . . . . . . . . . . . . . . . . . . . . . 17 Bialas, J. . . . . . . . . . . . . . . . 21, 25, 107 Blinova, V. . . . . . . . . . . . . . . . . . . . . 21 Blumenberg, M. . . . . . . . . . . . 119, 121 B旦nnemann, C. . . . . . . . . . . . . . 17, 96 Boetius, A.. . 19, 67, 72, 79, 98, 100, 137 Bohlen, T. . . . . . . . . . . . . . . . . . . . . 133 Bohrmann, G.. . . 8, 21, 23, 35, 65, 142 Breitzke, M. . . . . . . . . . . . . . . . . . . . 25 Broser, A. . . . . . . . . . . . . . . . . . . . . . 21 Br端ckmann, W. . . . . . . . . . . . . 8, 28, 94 B端nz, S. . . . . . . . . . . . . . . . . . . . . . . 29 C Chapman, N.R. . . . . . . . . . . . . . . . . 146 Conze, R. . . . . . . . . . . . . . . . . . . . . . 81 D Dahms, E. . . . . . . . . . . . . . . . . . . . . 145 Deerberg, G.. . . . . . . . . . . . . . 113, 116 Dieckmann, V.. . . . . . . . . . . . . . . . . . 91 Drews, M.. . . . . . . . . . . 21, 31, 33, 142

148

E Eisenhauer, A. . . . . . . . . . . . . . . . . . . 35 Elvert, M. . . . . . . . . . . . . . . . . . 19, 100 Eppelin, A. . . . . . . . . . . . . . . . . . . . . 72 Erbas, K. . . . . . . . . . . . . . . . . . . . . . . 53 Erzinger, J. . . . . . . . . . . . . . . . . 36, 145 F Fahlenkamp, H.. . . . . . . . . . . . 113, 116 Feeser, V.. . . . . . . . . . . . . . . . . . . . . . 46 Fischer, H. . . . . . . . . . . . . . . . . . . . . . 38 Fl端h, E. . . . . . . . . . . . . . . . . . . . . . . 107 Fouchet, J.-P.. . . . . . . . . . . . . . . . . . . 21 Freitag, J. . . . . . . . . . . . . . . . . . . . . . . 8 G Gajewski, D. . . . . . . . . . . . . . . . . . . 107 Gennerich, H.-H.. . . . . . . . . . . . 41, 139 GHOSTDABS cruise . . . . . . . . . . . . . . 93 Gieseke, A. . . . . . . . . . . . . . . . . . . . . 98 Goreshnik, E. . . . . . . . . . . . 59, 74, 128 Greinert, J. . . . . . . . . . . . 21, 44, 78, 83 Grevemeyer, I.. . . . . . . . . . . . . . 41, 139 Grupe, B. . . . . . . . . . . . . . . . . . . . . . 46 Gubsch, S. . . . . . . . . . . . . . 49, 78, 122 Gunkel, T. . . . . . . . . . . . . . . . . . . . . . 23 Gust, G. . . . . . . . . 31, 49, 78, 122, 131 Gutt, C. . . . . . . . . . . . . . . . . . . . . . . 14 H Haeckel, M. . . . . . . . . . . . . . . . . . . . 52 Halbach, P. . . . . . . . . . . . . . . . . 56, 102 Harris, J.M. . . . . . . . . . . . . . . . . . . . . 11 Heidersdorf, F.. . . . . . . . . . . . . . . . . . 21 Heinrich, T. . . . . . . . . . . . . . . . . . . . . 23

Index

Henninges, J. . . . . . . . . . . . . . . . . . . 53 Hensen, C. . . . . . . . . . . . . . . . . . . . . 63 Hoffmann, K. . . . . . . . . . . . . . . . . . . 46 Hohnberg, H.-J. . . . . . . . . . . . . . . . . . 9 Holscher B. . . . . . . . . . . . . . . . . . 31, 49 Holzbecher, E. . . . . . . . . . . . . . . . . . 102 Horsfield, B. . . . . . . . . . . . . . . . . . . . 91 Hübner, A. . . . . . . . . . . . . . . . . . . . . 56 Hübscher, C. . . . . . . . . . . . . . . . . . . 107 Huenges, E. . . . . . . . . . . . . . . . . . . . 53 Hyndman, R.D. . . . . . . . . . . . . . . . . 146 I Itoh, H. . . . . . . . . . . . . . . . . . . . . 59, 74 INGGAS working group . . . . . . 25, 107 Ivanov, M. . . . . . . . . . . . . . . . . . . . . . 21 J Janssen, S. . . . . . . . . . . . . . . . . . . . . 14 Jørgensen B.B. . . . . . . . . . . . . . . . . . 19 K Kasten, S. . . . . . . . . . . . . . . . . . . . . . 63 Kaul, N. . . . . . . . . . . . . . . . . . . 41, 139 Keir, R. . . . . . . . . . . . . . . . . . . . . . . . 44 Kipfstuhl, S. . . . . . . . . . . . . . . . . . . . . 8 Klages, M. . . . . . . . . . . . . . . . . . . . . 79 Klapproth, A. . . . . . . . . . . . . . . . 59, 74 Klaucke, I.. . . . . . . . . . . . . . . . . . 21, 65 Klein, G. . . . . . . . . . . . . . . . . . . . . . 133 Knittel, K. . . . . . . . . 19, 67, 79, 98, 137 Konerding, P. . . . . . . . . . . . . . . . . . . 85 Krastel, S. . . . . . . . . . . . . . . . 21, 69, 83 Kreiter, S. . . . . . . . . . . . . . . . . . . . . . 46

Krüger, M. . . . . . . . . . . . . . . . . . 19, 72 Krysiak, F. . . . . . . . . . . . . . . . . . . . . . 81 Kuhs, W.F. . . . . . . . . . . 23, 59, 74, 128 Kukowski, N. . . . . . . . . . . . . . . . . . . 36 Kulenkampff, J.. . . . . . . . . . . . . 76, 124 L Laframboise, R. . . . . . . . . . . . . . . . . . 81 Leder, T. . . . . . . . . . . . . . . . . . . . . . . 21 Lemke, A. . . . . . . . . . . . . . . . . . . 19, 67 Liebetrau, V. . . . . . . . . . . . . . . . . . . . 35 Linke, P. . . . . . . 23, 28, 35, 78, 94, 122 Lom-Keil, H. von . . . . . . . . . . . 83, 126 Lösekann, T. . . . . . . . . . . . . . . . . 19, 79 Löwner, R.. . . . . . . . . . . . . . . . . . . . . 81 Lüders, V. . . . . . . . . . . . . . . . . . 36, 109 Lüdmann, T. . . . . . . . . . . . . . . . . . . . 85 Luff, R. . . . . . . . . . . . . . . . . . . . . . . . 87 M Mallik working group . . . . . . . 11, 53, 81, 91, 143, 145 Mangelsdorf, K. . . . . . . . . . . . . . . . . 91 Meyer, H. . . . . . . . . . . . . . . . . . . . . . 17 Michaelis, W. . . . . . . . 93, 98, 119, 121 Mienert, J. . . . . . . . . . . . . . . . . . . . . 29 Mörz, T. . . . . . . . . . . . . . . . . . . . 28, 94 Möller, P.. . . . . . . . . . . . . . . . . . 36, 109 Müller, C. . . . . . . . . . . . . . . . . . . 17, 96 Müller, V. . . . . . . . . . . . . . . . . . . . . . 49

149

Index

N Nadalig, T.. . . . . . . . . . . . . . . . . . . . . 79 Nauhaus, K. . . . . . . . . . 19, 72, 98, 121 Naumann, R.. . . . . . . . . . . . . . . . 36, 76 Neben, S. . . . . . . . . . . . . . . . . . . 17, 96 Niemann, H. . . . . . . . . . . . . . . . 19, 100 O P Pape, T. . . . . . . . . . . . . . . . . . . . . . . 119 Peckmann, J.. . . . . . . . . . . . . . . . . . 105 Peterknecht, K. . . . . . . . . . . . . . . . . 119 Pfannkuche, O. . . . . . . . . . . . . . 78, 122 Polikarpov, I. . . . . . . . . . . . . . . . . . . . 21 Poser, M. . . . . . . . . . . . . . . . 28, 78, 94 Pratt, R.G. . . . . . . . . . . . . . . . . . . . . . 11 Press, W. . . . . . . . . . . . . . . . . . . . . . . 14 Q R Reichel, Th. . . . . . . . . . . . . . . . . . . . 102 Reimer, A. . . . . . . . . . . . . . . . . . . . . 105 Reitner, J. . . . . . . . . . . . . . . . . . . . . 105 Reston, T. . . . . . . . . . . . . . . . . . . . . 107 Rhein, M. . . . . . . . . . . . . . . . . . . . . 119 Richter, K.-U.. . . . . . . . . . . . . . . . . . . 38 Rickert, D.. . . . . . . . . . . . . . 23, 52, 137 Riedel, M. . . . . . . . . . . . . . . . . . . . . 146 S Saburova, M. . . . . . . . . . . . . . . . . . . 21 Salamatin, A.N. . . . . . . . . . . . . . . . . 128

150

Sauter, E. . . . . . . . . . . . . . . . . . . . . . 79 Savidis, S. . . . . . . . . . . . . . . . . . . . . . 46 Schellig, F. . . . . . . . . . . . . . . . . . . . . . 21 Schicks, J. . . . . . . . . . . . . . 36, 109, 145 Schlüter, M. . . . . . . . . . . . . . . . . . . . 79 Schlüter, S. . . . . . . . . . . . . . . . 113, 116 Schmale, O. . . . . . . . . . . . . . . . 21, 119 Schmaljohann, R. . . . . . . . . . . . . . . . 33 Schmidt, J. . . . . . . . . . . . . . . . . . . . . 19 Schmidt, M. . . . . . . . . . . . . . . . . . . 133 Schmidt-Brauns, J. . . . . . . . . . . . . . 111 Schneider, R. . . . . . . . . . . . . . . . . . . . 63 Schrötter, J.. . . . . . . . . . . . . . . . . . . . 53 Schultz, H.J. . . . . . . . . . . . . . . 113, 116 Schupp, J. . . . . . . . . . . . . . . . . . . . . . 46 Schwenk, T. . . . . . . . . . . . . . . 126, 146 Seifert, R. . . . . . . . . . . . . . 93, 119, 121 Shimizu, S. . . . . . . . . . . . . . . . . . . . . 11 Sommer, S. . . . . . . . . . . . . . . . . 78, 122 Spangenberg, E. . . . . . . . . . 36, 76, 124 Spieß, V. . . 21, 44, 63, 69, 83, 126, 146 Staykova, D. . . . . . . . . . . . . . . . . . . 128 Steffen, H. . . . . . . . . . . . . . . . . . . . 131 Suess, E. . . . . . . . . . . . . . . . 23, 52, 142 Sültenfuß, J. . . . . . . . . . . . . . . . . . . 119 T Techmer, K. . . . . . . . . . . . . . . . . . . . . 23 Teichert B.M.A. . . . . . . . . . . . . . . . . . 35 Theilen, Fr. . . . . . . . . . . . . . . . 107, 133 Thiel, V.. . . . . . . . . . . . . . . . . . 119, 121 Thießen, O. . . . . . . . . . . . . . . . . . . . 133 Treude, T. . . . . . . . . . . . 19, 72, 98, 137 Tse, J. . . . . . . . . . . . . . . . . . . . . . . . . 14 Türk, M. . . . . . . . . . . . . . . . . . . . 28, 94

Index

U V Viergutz, T. . . . . . . . . . . . . . . . . . . . . 49 Villinger, H. . . . . . . . . . . . . 41, 107, 139 Volkonskaya, A. . . . . . . . . . . . . . . . . 21 W W채chter, J. . . . . . . . . . . . . . . . . . . . . 81 Wallmann, K. . . 23, 31, 33, 52, 87, 142 Weber, M.H. . . . . . . . . . . . . . . 11, 143 Weinrebe, W. . . . . . . . . . . . . . . . 21, 65 Widdel, F. . . . . . . . . . . . 19, 72, 98, 121 Wiersberg, T.. . . . . . . . . . . . . . . . . . 145 Wilkes, H. . . . . . . . . . . . . . . . . . . . . . 91 Witte, U.. . . . . . . . . . . . . . . . . . . . . . 19 Wong, H.K.. . . . . . . . . . . . . . . . . . . . 85 X Y Z Zillmer, M.. . . . . . . . . . . . . . . . . . . . . 21 Zimmer, M. . . . . . . . . . . . . . . . . . . . 145 Zuehlsdorff, L.. . . . . . . . . . 69, 126, 146

151

Notes

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In Germany, the national gas hydrate programme “Gas Hydrates in the Geosystem” has been initiated in 2000 as part of the new R&D programme GEOTECHNOLOGIES, financed by the Federal Ministry for Education and Research (BMBF) and the German Research Council (DFG). The gas hydrate programme promotes a better understanding of the nature of hydrates, hydrate-bearing sediments, and the interaction between the global methane hydrate reservoir and the world’s oceans and atmosphere. Research projects covering a wide spectrum of science and technology, including geology, biogeochemistry, geophysics, physical chemistry and mechanical engineering. These are carried out in close collaboration between various national and international partners from academia and industry. Field studies are underway at the Cascadia Margin off western North America, in the Black Sea, the Mackenzie Delta of the northwestern Canadian Arctic, and off-shore Central-America and Central-Africa.

This abstract volume contains the presentations given during four topical sessions of the first status seminar “Gas Hydrates in the Geosystem” held at the GEOMAR Research Centre in Kiel, Germany. The abstracts reflect the multidisciplinary approach of the programme and provides an excellent overview of where current gas hydrate research in Germany stands.

Science Report GEOTECHNOLOGIEN

Natural gas hydrates as a potential (i) energy resource, (ii) factor in global climate change and (iii) trigger of submarine geohazard have received wide international attention in the past years.

Gas Hydrates in the Geosystem

Gas Hydrates in the Geosystem

GEOTECHNOLOGIEN Science Report

Gas Hydrates in the Geosystem Status Seminar GEOMAR Research Centre Kiel 6-7 May 2002

Programme & Abstracts

The GEOTECHNOLOGIES programme is financed by the Federal Ministry for Education and Research (BMBF) and the German Research Council (DFG)

No. 1

ISSN: 1619-7399

No. 1