Variability of Antarctic sea ice extent over the past 200 years

While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing, the extent of Antarctic sea ice showed a positive trend during 1979-2015, followed by an abrupt decrease. The shortness of the satellite record limits our ability to quantify the possible contribution of anthropogenic forcing and internal variability to the observed Antarctic sea ice variability. In this study, ice core and fast ice records with annual resolution from six sites are used to reconstruct the annual-resolved northernmost latitude of sea ice edge (NLSIE) for different sectors of the Southern Ocean, including the Weddell Sea (WS), Bellingshausen Sea (BS), Amundsen Sea (AS), Ross Sea (RS), and the Indian and western Pacific Ocean (IndWPac). The linear trends of the NLSIE are analyzed for each sector for the past 100-200 years and found to be -0.08°, -0.17°, +0.07°, +0.02°, and -0.03° per decade (≥95% confidence level) for the WS, BS, AS, RS, and IndWPac, respectively. For the entire Antarctic, our composite NLSIE shows a decreasing trend (-0.03° per decade, 99% confidence level) during the 20th century, with a rapid decline in the mid-1950s. It was not until the early 1980s that the observed increasing trend occurred. A comparison with major climate indices shows that the long-term linear trends in all five sectors are largely dominated by the changes in the Southern Annular Mode (SAM). The multi-decadal variability in WS, BS, and AS is dominated by the Interdecadal Pacific Oscillation, whereas that in the IndWPac and RS is dominated by the SAM.