Climate Forcing of the Terrestrial Organic Carbon Cycle During the Late Deglaciation: The Himalaya-Bengal Fan Example
Abstract ID: 248259
Christopher J. Hein (hein@vims.edu), Valier Galy (vgaly@whoi.edu), Hermann Kudrass (kudrass@gmx.de), Timothy I. Eglinton (timothy.eglinton@erdw.ethz.ch), Bernhard Peucker-Ehrenbrink (bpeucker@whoi.edu) 1
Decadal OC Reservoir (organic litter)
Sediment cores (117KL, 118KL, 120KL) from channel-levee record last 20 kyrs of sedimentation and OC export from G-B rivers.
bulk biospheric OC
Fig. 2. Ages of components of biospheric OC in sediments collected from G-B rivers. Error bars: 95% confidence interval; errors are within points where absent. C24+ FA & bulk biospheric data from Galy & Eglington (2011); lignin phenol data are unpublished.
High Freshwater 31 Inputs 32
34
iii.
Strong Monsoon -170
-160
BoB Shelf
BoB ChannelLevee System
Modern Rivers
0.72 -14 -16 -18
Modern Rivers
1
3
5
7
9 11 13 15 Age (ka B.P.)
17
19
21
Himalayan Front Rivers
Ganges River
Brahmaputra River
Confluent G-B River
Fig. 4. Sr & Nd isotopic composition of modern & Bengal Fan sediments (modified from Lupker et al., 2013). Channel-levee cores are the same as those used in this study (117KL, 118KL, 120KL). River-sediment analyses compiled, in part, from Galy et al. (1999) and Singh & France-Lanord (2002).
OC exported by each G-B rivers has significantly-distinct composition (Galy & Eglinton, 2011; Galy et al., 2011). Himalayas have unique Sr-Nd-Os signature compared to other local potential sediment sources (Galy et al., 2010). OC in Ganges Basin has shorter average RT & greater contribution of C4 plants than Brahmaputra Basin → need to account for changes in sediment & OC sources. Stable isotopic (Sr & Nd) compositions over 21 kyrs stable & consistent with modern G-B mixing (Fig. 4).
0.09 Reduced Strong Monsoon -200
-150
vi.
-140
-190 -180 -170
Weak Monsoon
-160
Weighted Ave. C24-32 FA
-150
C28 FA
-140
C3 Plants (forest) -29
-130 Weak Monsoon
B) i.
C3 Plants -24.0
-27 -25
-23.0
-23
-22.0
ii.
-21.0
C4 Plants (savanna)
-20.0
C3 Plants (forest) -31
iii.
-19.0
-29
-18.0 C4 Plants
Outlier (?)
-27
Weighted Ave. C24-32 FA
-25
C4 Plants -23 (savanna) High C Loading 0.8 Carbon Loading (TOC, %)
Cores
0.74
εNd
Explanation
0.10
v.
C28 FA
C)
i.
0.6
0.4 Low C Loading
High Loading 6.0
ii.
4.0 2.0
Rapid Deposition 5.0 4.0 3.0 2.0 1.0 0.0 Slow Deposition
0.0 Low Loading
iii.
es utra hna 0 g an ap eg G hm M a er r B ow L
2
4
6
8
12 10 Age (kyr B.P.)
14
16
18
20
Negative correlation between monsoon strength and RT of organic carbon in G-B system.
Trends slighly reversed since mid Holocene.
0.11
Fan Channel-Levee
Plant wax (n-alkanes & fatty acids [C24+FA]) δD record increase in monsoon strength; channel-levee C28 FA (this study) show 45 ‰ shift from H1 to HCO.
0.14 Enhanced
0.12
Bengal Shelf
RT calculated as difference between deposition age of C24+FA (from foram ages or core age model) & calibrated age of C24+FA .
-0.5
0.13
Climate Change Impacts on OC-Export Dynamics (Fig. 6):
BoB salinity decreases (decrease in δ18O of planktonic forams in sediment cores) & weathering in G-B Basin increases.
Shelf & channel-levee records largely similar; shifts smaller in shelf record → possible signal buffering by Indo-Burman inputs to shelf record.
-1.0
iv.
35 Low Freshwater Inputs
Terrestrial Leaf Wax Wt. Ave. C29 & C31 n-alkane δ13C (‰ VPDB)
Late Glacial
BøllingAllerød
-1.5
33
Terrestrial Leaf Wax Fatty Acid δ13C (‰ VPDB)
Sr/86Sr 87
0.76
H1
Younger Dryas
-2.0
0
Sedimentation Rate (mm/yr)
C24+ FA
5.0
Holocene Climatic Optimum
0.78
Younger Dryas BøllingAllerød
4. Sediment Contributions to the Bay of Bengal Since LGM
-2.5
ii.
0.5
Bulk Organic Carbon δ13C (‰ VPDB)
2.5
-3.0
1.0
Terrestrial OC Loading ([C24+], mg/gSed)
Ganges River suspended sed bedload sed Brahmaputra River suspended sed bedload sed Confluent G-B
1.5
Dry
Last Glacial Maximum (LGM) to Holocene Climatic Optima (HCO): Northern Hemisphere insolation increases → monsoon activity increases → moisture in G-B Basin increases.
i.
Sediment core age models provided by 14C dating of planktic foraminifera (G. ruber & G. sacculifer) (Weber et al., 1997; this study).
-20 Average age (kyrs.)
∆14C (‰)
activ e ch ann el
Sediment & organic carbon delivered to middle & lower fan in Bay of Bengal (BoB) via 2500-km long channel-levee system (Fig. 3).
+100
1.0
10 km
World’s largest fluvial sediment load (~10 t/yr; Galy & France-Lanord, 2001).
Marine Sediments
0.1
East
9
Rivers, Lakes
0
active channel
2.0
A)
Terrestrial Leaf Wax Fatty Acid δD (‰ VSMOW)
Transfer of “Young” Decadal OC to Rivers
2640
Fig. 3. Study area - G-B Basin and Bengal Fan. Red: sediment cores used in study. Seismic-reflection profile from mid-fan channel-levee of Bengal Fan (Weber et al., 1997).
Area of Detail
Approximate Fan Boundary
Age of biospheric OC Exported from G-B Rivers: Bulk biospheric OC (“fresh” + “aged”): 3000 yrs. “Aged” OC: >17 kyrs. - millennial OC “Young” OC: 50-1300 yrs. (decadal OC) - mix of compounds with different relative RTs, such as: ◦ Lignin-derived phenols: < 50 - ~100 yrs. ◦ n-alkanoic (fatty) acids (C24+ FA): ~400 yrs.
lignin phenols
2620
0o
Ganges-Brahmaputra (G-B) Rivers & Bay of Bengal: ~20% of global terrestrial biospheric OC burial (~3.9 x 1011 mol/yr; Galy et al., 2007, 2011).
-400
118KL
West
2. Organic-Carbon Export Dynamics in the Ganges-Brahmaputra Basin
-300
2600
2.5
Preliminary data: ca. 250 yr change in RT per 1 ‰ change in FA δD. Indicates likely mixing of millennial & decadal OC inputs. FA δD → decadal signal buffered by background millennial signal. Wetter climate → higher decadal input → shorter RT.
Vegetation Changes in the G-B Basin since LGM (Fig. 5b): 3 ‰ shift in δ C of bulk OC: transition of vegetation, C4 to C3 dominance, since LGM (Galy et al., 2008). 13
~5 ‰ shift in compound-specific δ13C of channel-levee C28 FA (this study) LGM to HCO. Compound-specific n-alkane (Bengal shelf) & C24+FA (channel-levee system) records show very similar trends. Muted reversal in vegetation type since HCO. Outlier: temporary C3 excursion during Bølling-Allerød? Source effect? Sediment & OC Burial in the BoB since LGM (Fig. 5c): No trends in OC burial or loading since LGM; C24+FA concentrations are consistent with G-B river sediments → high OC burial efficency. Large peaks in sediment burial in channel-levee system during & following Younger Dyras (similar to Goodbred & Kuehl, 2000).
Weak Monsoon -140 Terrestrial Leaf Wax Fatty Acid δD (‰ VSMOW)
Atmosphere
Fig. 1. Conceptual Model. (a) major pathways of carbon exchange between atmosphere, terrestrial vegetation, terrestrial “decadal” and “millennial” OC reservoirs and rivers. (b) simplified box model of OC transfer between atmospheric, terrestrial & marine reservoirs.
-200
117KL
Bengal Fan
Millennial OC Reservoir (soils, floodplains, riverbed, terraces)
-100
2580
Terrestrial Vascular Plants
Atmospheric CO2
Transfer of “Aged” Millennial OC to Export to Marine Rivers Sediments
Shelf
6. Climatic Control of Organic Carbon Residence Time in the G-B Basin
Climate Change in the G-B Basin since LGM (Fig. 5a):
Late Glacial
H1
Chemical Weathering (H2O+/Si*, mol:mol)
Remineralization to Atmosphere
2560
Wet
Holocene Climatic Optimum
δ18O (‰VPDB)
B)
120KL (projected)
120KL
117KL
2540
a
es
20o N
outer levee
hm a r B
Gang
Climate change affects cycling between terrestrial pools and timescales & sources of OC export to other reservoirs.
A)
Tibetan plateau Hima laya a putr
inner levees 118KL
Depth (m below sea level)
Terrestrial organic carbon (OC) reservoir subdivided into 3 pools: (1) “Petrogenic” (bedrock-derived); (2) “Aged” (Millennial) (stored in soils, floodplain, etc.); (3) “Young” (Decadal) (rapid turnover & export to ocean)
outer levee
90o E
Mean Effective Moisture
80o E
2
5. Monsoon Intensity, Paleo-vegetation, and Sediment / OC Burial Since LGM
3. Record Location: GangesBrahmaputra Basin / Bay of Bengal
Atmospheric CO2 affected by small changes in size & residence time (RT) of carbon in other reservoirs (terrestrial, oceans, etc).
4
Department of Physical Sciences, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA, USA; 2Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA USA; 3 MARUM - Zentrum für Marine Umweltwissenschaften Universität Bremen Leobener Straße 28359 Bremen, Germany; 4Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, ETH, 8092 Zurich, SWITZERLAND
Salinity (‰)
1. Climatic Forcing of Carbon Cycle Dynamics
3
Terrestrial Leaf Wax Wt. Ave. C29 & C31 n-alkane δD (‰ VSMOW)
1
2
-145 -150
y = 0.0035x - 177 R2: 0.728
-155 -160 -165 -170
y = 0.0043x - 183 R2: 0.763
-175 -180 -185
-190 Strong Monsoon 0
1000 2000 3000 4000 5000 6000 7000 8000 9000 Residence Time (yr)
Explanation Weighted Average C24-32 FA
C28 FA
C24-32 FA Regression Line
C28 FA Regression Line
Fig. 5. Records of climate changes, vegetation changes, and OC inputs to the BoB since LGM. Errors are within data points if error bars not shown. A) Climate change in the G-B / Bengal Basin since LGM. (i) “Effective moisture” in central Asia (Herzschuh, 2006). (ii) 3-pt. moving average of δ18O of planktonic forams (G.ruber) from BoB channel-levee cores SO93-117KL, 118KL, & 120KL (data: Weber et al., 1997 & Galy et al., 2008). (iii) BoB sea-surface salinity, as derived from foram δ18O record(Kudrass et al., 2001). (iv) Sediment hydration, a proxy for terrestrial chemical weathering, from the Bengal shelf (cores SO93-105KL & 107KL) and channel-levee system (cores SO93-117KL, 118KL, & 120KL) (Lupker et al., 2013). (v) Compound-specific hydrogen isotope compositions (rainfall intensity) of plant wax nalkanes from Bengal Shelf core SO188-342KL, sourced from Indo-Burman (I-B) range with possible contributions from G-B basin (Contreras-Rosales et al., 2014). (vi) Compound-specific hydrogen isotope compositions of plant wax n-alkanoic (fatty) acids from channel-levee cores, sourced solely from G-B basin (this study). B) Paleovegetation in the G-B Basin since LGM. (i) Compound-specific δ13C compositions (vegetation type sources) of plant wax n-alkanes from Bengal Shelf core SO188-342KL (Contreras-Rosales et al., 2014). (ii) 3-pt. moving average of bulk δ13C channel-levee cores (Galy et al., 2008; this study). (iii) Compound-specific δ13C compositions of plant wax n-alkanoic (fatty) acids from channel-levee cores (this study). B) Carbon loading in the Bay of Bengal. (i) Total organic carbon content from channel-levee cores (this study). (ii) Concentration (as a function of sediment mass) of long-chain (C24+ ), terrestrially derived fatty acids from channel-levee cores (this study). (iii) Updated sedimentation rate record for channel-levee core SO93-120KL based on calibrated foram radiocarbon ages (data from Weber et al., 1997; this study).
Fig. 6. Climatic control of OC residence time in the G-B River Basin. Comparison of stable hydrogen isotopic compositions (δD) and RT of terrestrial leaf wax FA. Note: errors within data points if error bars not shown.
7. Implications
Feedbacks: Climate Change & OC-Export Dynamics (Fig. 7): Negative correlation between monsoon strength & OC RT → background millennial contribution with variable decadal contribution. Glacial Period (Fig. 7a): weak monsoon → lower productivity and / or enhanced storage of OC in millennial stores → long OC RT. Holocene (Fig. 7b): warmer & strengthened monsoon → enhanced export of decadal OC (higher percentage of total OC export) & enhanced fixation of decadal OC → decadal OC reservoir increases → increased sequestration of atmospheric CO2 → negative feedback.
A)
Glacial Conditions
B)
Atmosphere Terrestrial Vascular Plants
Fig. 7. Climate / carbon-cycle feedbacks Simplified box models showing negative feedbacks between monsoon strength and terrestrial OC storage.
Decadal OC Reservoir (organic litter)
Holocene Conditions Atmosphere
Enhanced OC Storage in decadal Reservoir
Terrestrial Vascular Plants Decadal OC Reservoir (organic litter)
Millennial OC Reservoir (soils, floodplains, riverbed, terraces)
Millennial OC Reservoir (soils, floodplains, riverbed, terraces)
Ganges-Brahmaputra River
Ganges-Brahmaputra River
Bay of Bengal
Bay of Bengal
8. References Contreras-Rosales, L.A., Jennerjahn, T., Tharammal, T., Meyer, V., Lückge, A., Paul, A., Schefuß, E., 2014. Evolution of the Indian Summer Monsoon and terrestrial vegetation in the Bengal region during the past 18 ka. Quaternary Science Reviews, v. 102, p. 133-148. Galy, A., France-Lanord, C., 2001. Higher erosion rates in the Himalaya: geochemical constraints on riverine fluxes. Geology, v. 29, p. 23–26. Galy, A., France-Lanord, C., Derry, L.A., 1999. The strontium isotopic budget of Himalayan rivers in Nepal and Bangladesh. Geochimica et Cosmochimica Acta, v. 63, p. 1905-1925. Galy, V., Eglinton, T.I., 2011. Protracted storage of biospheric carbon in the Ganges-Brahmaputra basin. Nature Geoscience, v. 4, p.843-847. Galy, V., France-Lanord, C., Beyssac, O., Faure, P., Kudrass, H., Palhol, F., 2007. Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system. Nature, v. 450, p. 407–410. Galy, V., François, L., France-Lanord, C., Faure, P., Kudrass, H., Palhol, F., Singh, S.K., 2008. C4 plants decline in the Himalayan basin since the last glacial maximum. Quaternary Science Reviews, v. 27, p. 1396–1409. Galy, V., France-Lanord, C., Peucker-Ehrenbrink, B., Huyghe, P., 2010. Sr-Nd-Os evidence for a stable erosion regime in the Himalaya during the past 12 Myr. Earth and Planetary Science Letters, v. 290, p. 474-480. Galy, V., France-Lanord, C., Beyssac, O., Lartiges, B., Rhaman, M., 2011. Organic Carbon Cycling During Himalayan Erosion: Processes, Fluxes and Consequences for the Global Carbon Cycle. in: Lal, R., Sivakumar, M.V.K., Faiz, S.M.A.M.A., Mustafizur Rahman, A.H.M.H.M.M., Islam, K.R.R. (eds.), Climate Change and Food Security in South Asia. Netherlands: Springer, p. 163-181. Goodbred, Jr., S.L., and Kuehl, S.A., 2000. Enormous Ganges-Brahmaputra sediment load during strengthened early Holocene monsoon. Geology, v. 28, p. 1083-1086. Herzschuh, U., 2006. Palaeo-moisture evolution in monsoonal Central Asia during the last 50,000 years. Quaternary Science Reviews, v. 25, p. 163-178. Kudrass, H.R., Hofmann, A., Dosse, H., Emeis, K.-C., Erlenkeuser, H., 2001. Modulation and amplification of climatic changes in the Northern Hemisphere by the Indian summer monsoon during the past 80 k.y. Geology, v. 29, p. 63-66. Lupcker, M., France-Lanord, C., Galy, V., Lave, J., and Kudrass, H., 2013. Increasing chemical weathering in the Himalayan system since the Last Glacial Maximum. Earth and Planetary Science Letters, v. 365, p. 243-252. Singh, S., France-Lanord, C., 2002. Tracing the distribution of erosion in the Brahmaputra watershed from isotopic compositions of stream sediments. Earth and Planetary Science Letters, v. 252, p. 645-662. Weber, M.E., Wiedicke, M.H., Kudrass, H.R., Hübscher, C., Erienkeuser, H., 1997. Active growth of the Bengal Fan during sea-level rise and highstand. Geology, v. 25, p. 315-318.
9. Acknowledgments
This work was funded by NSF OCE Grants 133826 (Virginia Institute of Marine Science), 1333387 (Woods Hole Oceanographic Institution; WHOI), and 0928582 (WHOI). C. Hein was partially funded by the WHOI Coastal Ocean Institute Postdoctoral Scholar program. Significant analytical contributions and laboratory assistance were provided by X. Philippon, C. Johnson, S. Sylva & K. Fornace of WHOI & A. McNichol & the staff of the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS).