CT1. Heat, mass and momentum exchanges - The convergence and conversion of heat, mass and momentum at high latitudes is a fundamental component of the global energy budget. In order to reduce uncertainties in sea ice predictions and projections on seasonal to centennial timescales in both the Arctic and Antarctic, we need to better represent the crucial interactions and feedbacks between the OIA and the biological system. One of the key uncertainties is knowledge of the role of snow on sea ice within the OIA system. Snow and sea ice control the surface albedo and energy exchanges between atmosphere and ocean and are thus a critical component of the Earth’s climate system. Especially for snow on sea ice, there is a lack of representative observations, large uncertainties in existing observations, and challenges to represent snow-on-sea-ice processes in models. There are uncertainties in sea-ice related processes, for example the radiative transfer through snow and ice and the turbulent heat and momentum exchanges at the ice-atmosphere and ice-ocean interfaces. Current climate models fail to resolve many known small scale/non-homogeneous sea-ice and snow processes. These processes affect aerosols and clouds (CT2) and biogeochemistry/greenhouse gas exchanges (CT3) which influence coupled system behavior (CT4).

CT3. Biogeochemical cycles/greenhouse gas exchange - Changes in snow and sea ice, and ocean dynamics (CT1) are crucial for biological production and thus marine uptake of anthropogenic carbon at high latitudes and transport of biogeochemical properties into the ocean interior. However, ESMs still have considerable difficulties in reproducing these processes. Further, sea ice and snow are still treated as biogeochemically inert in most large-scale models, while they are now known to play an active role in biogeochemical processes, such as gas exchange. New descriptions of how sea ice/snow affect gas, aerosol (CT2), nutrient and carbon exchange between atmosphere and ocean are needed to make reliable future predictions. Uncertainties in gas transport across polar air-sea interfaces and related processes limit our ability to predict carbon storage, ocean acidification and ocean oxygen content in models. Biogeochemical cycling and greenhouse gas exchanges are interlinked with the physical state of the atmosphere, ice, and ocean (CT1) and are linked to aerosol processes, such as aerosol formation and nutrients delivered through aerosol deposition (CT2). These interlinkages are fully addressed within CT4.