Model sensitivity in the effect of Antarctic sea ice and stratification on atmospheric pCO 2

Several recent papers have demonstrated a decrease in atmospheric pCO 2 resulting from barriers to communication between the deep sea and the atmosphere in the Southern Ocean. Stephens and Keeling [2000] decreased pCO 2 by increasing Antarctic sea ice in a seven‐box model of the world ocean, and Toggweiler [1999] showed a similar response to Southern Ocean stratification. In box models the pCO 2 of the atmosphere is controlled by the region of the surface ocean that fills the deep sea [ Archer et al. , 2000a]. By severing the Southern Ocean link between the deep sea and the atmosphere, atmospheric pCO 2 in these models is controlled elsewhere and typically declines, although the models range widely in their responses. “Continuum models,” such as three‐dimensional (3‐D) and 2‐D general circulation models, control pCO 2 in a more distributed way and do not exhibit box model sensitivity to high‐latitude sea ice or presumably stratification. There is still uncertainty about the high‐latitude sensitivity of the real ocean. Until these model sensitivities can be resolved, glacial pCO 2 hypotheses and interpretations based on Southern Ocean barrier mechanisms (see above mentioned references plus Elderfield and Rickaby [2000], Francois et al. [1998], Gildor and Tziperman [2001], Sigman and Boyle [2000], and Watson et al. [2000]) are walking on thin ice.