Model sensitivity in the effect of Antarctic sea ice and stratification on atmospheric pCO₂

David E. Archer, Pamela A. Martin, and Carrie Ashendel, Department of Geophysical Sciences, University of Chicago, Chicago, IL, USA

Jose Milovich, Lawrence Livermore National Laboratory, Livermore, CA, USA

Viktor Brovkin, Potsdam Institute for Climate Impact Research, Potsdam, Germany

Gian-Kasper Plattner¹, Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
¹Now at Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California, USA

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 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 (above plus [Elderfield and Rickaby, 2000; Francois et al., 1998; Gildor and Tziperman, 2001; Sigman and Boyle, 2000; Watson et al., 2000]) are walking on thin ice.