We compare the sensitivity of the partial pressure of CO2 in the warm surface ocean and atmosphere to the influence of the ocean's cold water outcrops in a wide spectrum of models. While in simple box models the cold ocean dominates, in three-dimensional ocean general circulation models, this influence is considerably smaller, suggesting that exchange processes between the warm and cold regime in the real ocean are extremely important in determining the distribution of chemical properties. ¿ 1999 American Geophysical Union