• sea ice;
  • Antarctic;
  • climate;
  • passive microwave;
  • Southern Ocean

[1] The principal characteristics of the variability of Antarctic sea ice cover as previously described from satellite passive microwave observations are also evident in a systematically calibrated and analyzed data set for 20.2 years (1979–1998). The total Antarctic sea ice extent (concentration >15%) increased by 11,180 ± 4190 km2 yr−1 (0.98 ± 0.37% (decade)−1). The increase in the area of sea ice within the extent boundary is similar (10,860 ± 3720 km2 yr−1 and 1.26 ± 0.43% (decade)−1). Regionally, the trends in extent are positive in the Weddel Sea (1.4 ± 0.9% (decade)−1), Pacific Ocean (2.0 ± 1.4% (decade)−1), and Ross (6.7 ± 1.1% (decade)−1) sectors, slightly negative in the Indian Ocean (−1.0 ± 1.0% (decade)−1), and strongly negative in the Bellingshausen-Amundsen Seas sector (−9.7 ± 1.5% (decade)−1)). For the entire ice pack, ice increases occur in all seasons, with the largest increase during fall. On a regional basis the trends differ season to season. During summer and fall the trends are positive or near zero in all sectors except the Bellingshausen-Amundsen Seas sector. During winter and spring the trends are negative or near zero in all sectors except the Ross Sea, which has positive trends in all seasons. Components of interannual variability with periods of about 3–5 years are regionally large but tend to counterbalance each other in the total ice pack. The interannual variability of the annual mean sea ice extent is only 1.6% overall, compared to 6–9% in each of five regional sectors. Analysis of the relation between regional sea ice extents and spatially averaged surface temperatures over the ice pack gives an overall sensitivity between winter ice cover and temperature of −0.7% change in sea ice extent per degree Kelvin. For summer some regional ice extents vary positively with temperature, and others vary negatively. The observed increase in Antarctic sea ice cover is counter to the observed decreases in the Arctic. It is also qualitatively consistent with the counterintuitive prediction of a global atmospheric-ocean model of increasing sea ice around Antarctica with climate warming due to the stabilizing effects of increased snowfall on the Southern Ocean.