Sea-ice ridges – key yet understudied component of the coupled Arctic sea-ice system

Sea-ice ridges constitute a large fraction of the Arctic ice pack. However, the few published estimates of the sea-ice fraction in ridges vary from 10 to 70%. Ridges affect key ice-ocean and ice-atmosphere exchange processes and are potential biological hotspots. Nevertheless, we know disproportionally little about the role of ridges in the coupled Arctic sea-ice system. Here recent findings are summarized, including targeted interdisciplinary observations of sea-ice ridges during the year-long MOSAiC drift expedition across the Arctic. The dynamic and seasonally evolving nature of sea-ice ridges is highlighted and the diverse types of habitats they can provide, much more than that in level ice, for ice-associated flora and fauna. Recent observations during the MOSAiC expedition suggest that in summer 80% of ice algal biomass could reside in ridges. While being biological hotspots in Arctic summer, ridge formation in winter could supply organic material to feed the pelagic food web during the polar night. To fully understand the Arctic icescape and the changes occurring, we must not only place much more effort to understand the intricate physical and biological processes occurring in sea-ice ridges but also include these processes in coupled models.