Did Antarctic sea-ice expansion cause glacial CO2 decline? -: art. no. 1011

[1] Recently, Stephens and Keeling [2000] have put forward an appealing theory for explaining the decrease in glacial atmospheric CO2. They argue that a compact sea-ice cover extending southward of similar to55degrees S trapped large amounts of CO2 beneath the sea surface, thus accounting for the lower atmospheric concentrations. An atmosphere-ocean box model in which sea-ice area is prescribed allows them to simulate similar to80% of the CO2 drawdown. However, glacial CO2 levels can be attained in their model only when the fraction of ice-covered area southward of the Antarctic Polar Front rises to 99-100%. We present simulations with a coupled sea ice-upper ocean model indicating that ice-area fractions so large might have not prevailed even under rather extreme glacial conditions. The combination of our glacial ice-coverage estimates with the ice area-CO2 relation derived by Stephens and Keeling suggests that CO2 sequestration under sea ice could account for at most 15-50% of the total glacial CO2 decline.