The Arctic summer sea ice continues declining, with the third-lowest extent in satellite record reached in September 2010. This sustained reduction evokes predictions and speculations about the fate of the Arctic sea ice cap and the Arctic system as a whole. The past decade showed also extraordinarily high ocean temperatures due to very warm inflow from the Atlantic and Pacific oceans accompanied by a substantial freshening of the upper ocean. The intriguing coincidence of these evolutions raises the question of interactions or common causes. Possible reasons for current changes are seen in large-scale circulation changes with partly unclear connection to the ongoing global warming. The efforts of the International Polar Year 2007-2008 and international programmes as DAMOCLES, SEARCH and others have enhanced the data flow from ice and ocean observations and contributed to improving modelling abilities from local to regional and global scales. The models are also progressing through increased model resolution and improved model physics. All these advance our understanding of the Arctic system. For this session we encourage presentations on observed and simulated changes in the Arctic ocean, atmosphere and ice, on their mutual interaction and on the interaction with the global processes. We are interested in studies concerning decadal scale as well as in short time scale. Discussion of future scenarios of the Arctic system are welcome.