Abstract
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 ∼55° 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 ∼80% 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.
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