A first estimate of present and preindustrial air‐sea CO₂ flux patterns based on ocean interior carbon measurements and models

The exchange of CO 2 across the air‐sea interface is a main determinant of the distribution of atmospheric CO 2 from which major conclusions about the carbon cycle are drawn, yet our knowledge of atmosphere‐ocean fluxes still has major gaps. A new analysis based on recent ocean dissolved inorganic carbon data and on models permits us to separately estimate the preindustrial and present air‐sea CO 2 flux distributions without requiring knowledge of the gas exchange coefficient. We find a smaller carbon sink at mid to high latitudes of the southern hemisphere than previous data based estimates and a shift of ocean uptake to lower latitude regions compared to estimates and simulations. The total uptake of anthropogenic CO 2 for 1990 is 1.8 (±0.4) Pg C yr −1 . Our ocean based results support the interpretation of the latitudinal distribution of atmospheric CO 2 data as evidence for a large northern hemisphere land carbon sink.