a) Significance

Near-future climate change is predicted to have its strongest impact in polar regions due to direct changes in surface area of polar oceans and ice sheets and to subsequent feedback processes. At both poles, climate change is already apparent in reduced sea ice extent. In the Antarctic, reductions in sea-ice cover are observed in the Bellingshausen/Amundsen seas (Cavalieri and Parkinson 2008). In the Arctic region, both ice extent and thickness are reducing rapidly, with a record low summer ice extent in 2007. The observed reductions appear to be ahead in time of current model forecasts (Perovich and Richter-Menge 2009), illustrating both the rapidity of the observed change and the difficulty of understanding and modeling all the feedbacks involved in the change. Current global models include the seasonal wax and wane of sea ice, but restrict associated properties to only a few physical features. In such models, sea ice’s main impact is on Earth’s radiative balance through its albedo, on deepwater formation and on air-sea-exchange processes of gases. The latter impact refers to sea ice as a “cap ” on the ocean surface (Stephens and Keeling 2000). Emerging views indicate, however, that sea ice itself plays an important role in the biogeochemical cycling and exchange of climate gases. A better understanding of these processes is warranted in order to improve climate change models and associated feedbacks. It is important t