Antarctic Sea Ice History, Late Quaternary

Sea ice results from the freezing of surface sea water. In the Southern Ocean, sea ice surrounds the Antarctic continent and it today covers 20 × 10 km in winter and only 4 × 10 km in summer (Gloersen et al., 1992). This pronounced seasonal cycle strongly affects the climate of the Southern Hemisphere through its impacts on the energy and gas budget, on the atmospheric circulation, on the hydrological cycle, and on the biological productivity (Figure A21). Sea ice also modulates the climate of remote places through its impact on the deep and intermediate oceanic circulations. More details about sea ice formation, seasonal cycle and its importance in the climate and ocean systems can be found in the entry on Arctic sea ice, this volume. Sea ice is a very reactive component of the cryosphere that has experienced drastic changes through time. Whaling ship records (de la Mare, 1997), satellite measurements (Cavalieri et al., 2003), and ice core data (Curran et al., 2003) indicate that Antarctic sea ice underwent a dramatic decrease in maximum extent since the 1950s. Such a reduction may accelerate in the near future because of global warming, and this will in turn have important feedbacks on future climate. However, sea ice is still not well-computed in climate models because of its complicated relationship to climate change over a large range of timescales. One way to ameliorate our understanding of such relationship is to reconstruct sea ice extent over long time periods and certain key periods for which the global climate is reasonably well-known. These reconstructions that started in the early 1980s are still very sparse in numbers and coverage because of the scarcity of good sediment sequences in the Southern Ocean. Three long records from the Atlantic and Indian sectors of the Southern Ocean are presented here to give an idea of sea ice dynamics over the last two climatic cycles, and then present a map of winter and summer sea ice extent at the Last Glacial Maximum (LGM) is also shown to illustrate sea ice distribution under a very different climatic state from the present.