Several recent papers have demonstrated a decrease in atmospheric pCO₂ resulting from barriers to communication between the deep sea and the atmosphere in the Southern Ocean. Stephens and Keeling [2000] decreased pCO₂ 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 pCO₂ 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 pCO₂ 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 pCO₂ 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 pCO₂ 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.