The influence of antarctic sea ice on glacial-interglacial CO₂ variations

Ice-core measurements indicate that atmospheric CO₂ concentrations during glacial periods were consistently about 80 parts per million lower than during interglacial periods. Previous explanations for this observation have typically had difficulty accounting for either the estimated glacial O₂ concentrations in the deep sea, ¹³C/¹²C ratios in Antarctic surface waters, or the depth of calcite saturation; also lacking is an explanation for the strong link between atmospheric CO₂ and Antarctic air temperature. There is growing evidence that the amount of deep water upwelling at low latitudes is significantly overestimated in most ocean general circulation models and simpler box models previously used to investigate this problem. Here we use a box model with south of 55 °S to investigate the deep-water upwelling confined to glacial-interglacial linkages between Antarctic air temperature and atmospheric CO₂ variations. We suggest that low glacial atmospheric CO₂ levels might result from reduced deep-water ventilation associated with either year-round Antarctic sea-ice coverage, or wintertime coverage combined with ice-induced stratification during the summer. The model presented here reproduces 67 parts per million of the observed glacial- interglacial CO₂ difference, as a result of reduced air-sea gas exchange in the Antarctic region, and is generally consistent with the additional observational constraints.