Polar Cod and Zooplankton
A peek beneath the surface of Arctic sea ice
Sea Ice Algae
Sea ice ridges account for a large proportion of the overall Arctic sea ice volume, yet more attention in research has historically been focused on the thinner level ice. We spoke to Dr Mats Granskog and Dr Oliver Müller about their work in analysing samples from sea ice ridges collected during the MOSAiC polar expedition, with the aim of gaining deeper insights into their role.
A significant proportion of the overall Arctic sea ice volume is comprised of ridges, which can be thought of in a way as a pile of lego bricks, much of which is submerged below the ocean surface. Usually sea ice is formed of a fairly level sheet, but when ice floes collide big blocks are created, which pile up in a large, random maze. “That creates a very different type of ice mass, and potentially a unique habitat for flora and fauna,” says Dr Mats Granskog, a Senior Researcher at the Norwegian Polar Institute. As part of his work in the HAVOC project, Dr Granskog is investigating the importance of these sea ice ridges and the role they play in providing a protective environment for certain iceassociated flora and fauna. “In the project we are primarily interested in what’s happening in the underwater part of sea ice ridges, as that’s the primary habitat for the biology we are looking at,” he outlines. “There’s a kind of maze of ice blocks, with water running in between.”
MOSAiC polar expedition
These sea ice ridges have not really been the focus of much attention in research, as a lot of time and resources are required to investigate them. More studies have been conducted on the level ice, which is relatively thin and homogenous, and so easier to study than sea ice ridges. “The more deformed parts and the sea ice ridges haven’t really been studied as intensively,” says Dr Granskog. This is an imbalance Dr Granskog is working to address in the HAVOC project, in which he and his colleagues are analysing samples collected from sea ice ridge environments during the MOSAiC polar expedition (led by the German Alfred Wegener Institute), which drifted across the central Arctic Ocean (AWI) between September 2019 and October 2020. “The plan with MOSAiC was to collect data in all seasons and so develop a deeper understanding of what’s happening in the Arctic and what’s driving the changes that we’re seeing,” he explains.
The HAVOC project was designed to take part in the MOSAiC expedition, which gave Dr Granskog and his colleagues the opportunity to gather physical and biological samples from sea ice ridges over a longer period. There are only few studies that investigated sea ice ridges, but those few examples suggest that ridges are hot-spots for biological life. “These sea ice ridges create habitats, like water-filled voids between ice blocks, which are protected from the currents,” says Dr Oliver Müller, a postdoctoral researcher working on HAVOC. Researchers collected samples from sea ice ridges at certain time points over the course of the MOSAiC expedition, aiming to build a fuller picture of the flora and fauna which can be found in them at different times of the year. A variety of sampling procedures were used in HAVOC, with researchers gathering not just water and ice samples at different depths of the ridge, but also catching organisms and particles associated with the ridge. “We used sediment traps, which
are cylinders that collect sinking material. If more biological activity is associated with a ridge, you would also expect more things to be released and seep out, like small organisms and organic matter,” explains Dr Müller. “There was a collaborating team from AWI that operated a Remotely Operated Vehicle (ROV). We designed a small sampling device that was taken with the ROV to the ridge to collect biological material. It also used bio-optical sensors to estimate the level of biological activity.” This provides a solid foundation for researchers in the project to investigate sea ice ridges and gain deeper insights into their ecological role. The original hypothesis was that sea ice ridges provide a kind of protective environment for flora and fauna, as they are quite thick and have a more complex structure
working on the biological and physical data that was collected. A lot of post-fieldwork analysis has been conducted and with the lab-based work now largely complete, the current focus of Dr Müller’s attention is on data analysis. “We’re essentially putting these pieces of the puzzle back together, linking physical data with biological processes that we’ve measured,” he outlines. In order to identify and understand the ecological connections, researchers have to first analyse a lot of different types of samples; now Dr Müller is working through the data, which is a big task. “There are huge amounts of data, including some really novel sequencing data. This provides a very detailed, genomic fingerprint of the biological community inside these ridges,” he continues.
“We are primarily interested in what’s happening in the underwater part of sea ice ridges, as that’s the unique habitat for the biology we are looking at. There’s a kind of maze of ice blocks in these ridges, creating pockets of water, protected from the outside.”
than the thinner level ice that melts in summer. “The thinner level ice would melt earlier in the season, and these ridges would then be able to give the ice-associated flora and fauna a refuge,” explains Dr Müller. It is however challenging to monitor the abundance of flora and fauna within sea ice ridges, as these ridges are very heterogenous and it’s difficult to follow the same single ridge for a sustained period. “You might at first find a spot which has a lot of abundance, and then the next time you find a spot which has less, just because of the diverse nature of these ridges. However, there are some indicators that we can measure,” continues Dr Müller.
Data analysis
The MOSAiC expedition itself concluded in October 2020, and researchers are currently
The physical data from the project has also been rigorously analysed, leading to a deeper understanding of how sea ice ridges function and evolve over time. The next step then will be to connect this work to the ecosystem and biological dimension, which Dr Granskog hopes will stimulate further investigation into sea ice ridges. “We hope to help build a research community. There are still many unresolved questions in this area, especially with respect to biological activity and the role of sea ice ridges in the Arctic system,” he outlines. The project’s research could also hold wider relevance to the development of climate models. “Ridges are not very well described in current climate models, yet evidence suggests that they are quite important in this respect,” continues Dr Granskog.
HAVOC
Ridges - Safe HAVens for ice-associated flora and fauna in a seasonally ice-covered Arctic OCean
Project Objectives
To better understand the role of sea ice ridges in the Arctic Ocean, given they might be the last sanctuary for ice-dependent organisms, when the thinner sea ice around the ridges melts away. While ridges constitute a major part of the sea ice volume in the Arctic Ocean, we know very little of their role in shaping the physical environment and as a habitat.
Project Funding
Research Council of Norway, H2020 ARICE DearICE and Hanse Wissenschaftskolleg.
Project Partners
Norwegian Polar Institute (Norway), Norwegian University of Science and Technology (Norway), UiT – The Arctic University of Norway (Norway), University of Bergen (Norway), NORCE Norwegian Research Centre (Norway), Akvaplan-Niva (Norway), The University Centre in Svalbard (Norway), and Alfred Wegener Institute (Germany).
Contact Details
Project Principal Investigator
Mats Granskog, Ph.D, Senior Researcher, Norwegian Polar Institute, Fram Centre, Tromsø, Norway
E: mats.granskog@npolar.no W: https://www.npolar.no/en/projects/havoc/
Dr Mats Granskog
Dr Oliver Müller Salganik, E., Lange, B. A., Katlein, C., Matero, I., Anhaus, P., Muilwijk, M., Høyland, K. V, & Granskog, M. A. (2023). Observations of preferential summer melt of Arctic sea-ice ridge keels from repeated multibeam sonar surveys. The Cryosphere, 17, 4873–4887. https://doi. org/10.5194/tc-17-4873-2023
Dr Mats Granskog is a Senior Research Scientist at the Norwegian Polar Institute. His research interests include the Arctic sea ice mass balance, physical-chemical-biological coupling in Arctic sea ice and upper ocean, and marine optics. He is also a fellow at the HanseWissenschaftskolleg (Delmenhorst, Germany).
Dr Oliver Müller is a post-doctoral researcher in the marine microbiology group at the University of Bergen. Alongside his work on the HAVOC project, he is also investigating the ecosystem of the northern Barents Sea.
