Antarctic sea ice variability and trends, 1979-2010

In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978-December 2010 reveal an overall positive trend in ice extents of 17 100 +/- 2300 km(2) yr(-1). Much of the increase, at 13 700 +/- 1500 km(2) yr(-1), has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has (like the Arctic) instead experienced significant sea ice decreases, with an overall ice extent trend of -8200 +/- 1200 km(2) yr(-1). When examined through the annual cycle over the 32-yr period 1979-2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 +/- 6300 km(2) yr(-1) in February to a high of 24 700 +/- 10 000 km(2) yr(-1) in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but the magnitudes of the two trends differ, and in some cases these differences allow inferences about the corresponding changes in sea ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.