Having meanwhile lost almost half of its summer sea ice extent, the Arctic Ocean seems to continue its transition towards a seasonally ice-free ocean. The sustained ice reduction evokes speculations about the reaction of the Arctic system as a whole. The past decades showed also extraordinarily freshening of the upper ocean and very warm inflow from the Atlantic and Pacific oceans. 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 other international programmes have enhanced the data flow from ice and ocean observations and contributed to improving modeling 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. 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. Discussion of future scenarios of the Arctic system is welcome.