One process that has been proposed to explain the glacial-interglacial change in atmospheric CO2 is a change in the strength of the ocean's biological pump, that is, changes in ocean export bioproductivity. Using a coupled ocean-atmosphere box model that incorporates carbon chemistry and a nutrient budget, we investigate the effect on atmospheric CO2 levels of changes to ocean export productivity in different regions. The primary discovery is the role of water column stratification in controlling the extent to which atmospheric CO2 is affected by regional changes in the biological pump. Stratification manifests itself in two competing ways. On the one hand, increasing stratification causes an increase in atmospheric CO2 sensitivity to export bioproductivity. This results in modeled CO2 being almost an order of magnitude more sensitive to low-latitude bioproductivity changes than it is to high-latitude changes. On the other hand, increasing stratification decreases the rate at which nutrients mix up into the surface layer, thereby setting a limit on the overall magnitude of bioproductivity increase and atmosphere CO2 decrease that is possible in stratified ocean regions. One of the implications of this work is to point to the potential importance of changes in the strength of low-latitude ocean bioproductivity as a cause of the glacial-interglacial atmospheric CO2 change. ¿ 1999 American Geophysical Union