Palaeoceanography. Antarctic stratification and glacial CO2

One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis, which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica. As discussed by Sigman and Boyle, this hypothesis assumes that increased stratification in the Antarctic zone (Fig. 1) was associated with reduced upwelling of deep waters around Antarctica, thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline, which is consistent with Antarctic sediment records. We point out here, however, that the response of ocean eddies to increased Antarctic stratification can be expected to increase, rather than reduce, the upwelling rate of deep waters around Antarctica. The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods.