Ridges - Safe Havens for ice-associated Flora and Fauna in a Seasonally ice-covered Arctic Ocean (HAVOC)

The HAVOC project aims to understand the role of sea-ice ridges, that is sea ice that has been pushed together and formed deep keels and high sails from blocks of ice, as a habitat for the sea-ice associated ecosystem in the central Arctic Ocean. With younger and thinner sea ice, a larger fraction of sea ice will melt every summer, and the last remnants of the ice that can survive summer melt, will be composed of thicker parts of the ice cover, often ridges. Ridges may thus be the last remnant of the sea ice pack that can be used by species that are dependent on sea ice for survival. Ridges are the least studied component of the sea ice cover, in part due to difficulties in the field. The international MOSAiC expedition took place from September 2019 to early Oct 2020 and replicated the drift of the Fram by Nansen in 1893-1896. However, this time the ice drifted much faster than in Nansen's time. The project participated in the drift during two periods (Dec 2019 - Feb 2020 and June-Aug 2020), and this provided a unique opportunity to study the evolution of sea-ice ridges, their physical impact on the surroundings, and how they function as a habitat. The first results from analysis of data shows that the ridges are different from the surrounding level ice in several ways, and there are some signs that the physical environment in ridges contributes to a different biogeochemistry. We also have unique data that that suggest that ridges rapidly consolidate in summer due to snow meltwaters infiltrating the ridges, while the rest of the ice pack is melting, this again might affect their mechanical strength and how they survive summer melt. The work also suggests thatwinter the accumulation of snow into nearby leads can result in rapid consolidation of ridge keels, a mechanisms that has not been suggested before, when otherwise ridge keels would consolidate very slowly.

This project will fill critical knowledge gaps on the functioning of the sea-ice associated ecosystem in the central Arctic Ocean. Our understanding of the key processes is simply outdated for us to fully understand the current conditions and to predict the future. A better process understanding is required to improve climate models and thus our ability to forecast the future. To date, essential information on the impact of ocean warming on ice ecosystems especially with regard to seasonal variations is lacking, which is largely related to the difficulties of conducting such observations over time periods relevant for understanding all the interactions in the Polar climate system. For improved process understanding annual time series are pivotal to understand these interactions and feedbacks. MOSAiC, an extensive international ice drift experiment, will study the central Arctic over full year cycle in 2019/2020, giving an unprecedented opportunity to understand the processes in a thinner ice pack. MOSAiC will provide unique insights on the atmosphere-ice-ocean system and add important knowledge on the processes in the Arctic ecosystem especially during seasons that are under-sampled so far (late autumn, winter, and early spring). Our work will examine the role of sea-ice ridges, one of the least studied features of the ice pack, to better understand their role in sea-ice cover that has become seasonal and melts in summer. Ridges may provide the last habitat and optimal refuge for organisms that are dependent on sea ice, while the ice otherwise would melt in summer. Thus ridges become a key component for ice-associated organisms to survive and a hot spot for diversity. Data we collect throughout a full-year cycle is used to improve representation of these processes in coupled-ice ocean and ecosystem models that contribute to an improved capacity to predict future conditions. This will be an essential contribution for the management of the Norwegian Arctic.