Antarctic sea ice variability and trends, 1979-2006

Analyses of 28 years (1979-2006) of Antarctic sea ice extents and areas derived from satellite passive microwave radiometers are presented and placed in the context of results obtained previously for the 20-year period 1979-1998. We present monthly averaged sea ice extents and areas, monthly deviations, yearly and seasonal averages, and their trends for the Southern Hemisphere as a whole and for each of five sectors: the Weddell Sea, the Indian Ocean, the western Pacific Ocean, the Ross Sea, and the Bellingshausen/Amundsen seas. The total Antarctic sea ice extent trend increased slightly, from 0.96 +/- 0.61% decade(-1) to 1.0 +/- 0.4% decade(-1), from the 20- to 28-year period, reflecting contrasting changes in the sector trends. The eight additional years resulted in smaller positive yearly trends in sea ice extent for the Weddell Sea (0.80 +/- 1.4% decade(-1)), the western Pacific Ocean (1.4 +/- 1.9% decade(-1)), and the Ross Sea (4.4 +/- 1.7% decade(-1)) sectors, a lessening of the negative trend for the Bellingshausen/Amundsen seas (-5.4 +/- 1.9% decade(-1)) sector, and a shift from a negative trend to a positive trend for the Indian Ocean ( 1.9 +/- 1.4% decade(-1)) sector. The trends for the Southern Hemisphere as a whole and for the Ross Sea sector are significant at the 95% level, whereas the trend for the Bellingshausen/Amundsen seas sector is significant at the 99% level. A similar pattern of yearly trend changes for the two periods is also apparent in the sea ice area time series.