Changes of the Thickness and Extent in the Sea-Ice:
In recent years, the sea ice that covers large parts of the Southern Ocean and of the Arctic Ocean has evolved in strikingly different ways. In the Arctic, the volume of sea ice has decreased substantially, in particular in summer. Both thickness and extent have decreased by about 50 % throughout the past decades. In the Antarctic, however, there seems to be even a small increase in sea-ice coverage.
These differences come about by the different geographic setting. In the Arctic Ocean, the ice is largely trapped by the surrounding land masses. Hence, its extent depends primarily on air temperature. In the Southern Ocean, sea ice instead free to drift. There, its extent depends primarily on wind patterns and oceanic temperature.