We reevaluate the isotopic air-sea disequilibrium of CO2 on the basis of a new high-quality global data set of surface observations of the reduced isotopic ratio (δ13C) of dissolved inorganic carbon (DIC). We find a global mean isotopic air-sea disequilibrium of 0.62±0.10 permil for 1990. Inserting our estimate into an anthropogenic 13C budget for the period from 1985 to 1995 yields an oceanic uptake of 1.5±0.9 Pg C yr−1, within the range of most other estimates. The large uncertainty of this estimate could be reduced with (i) better characterization of the surface ocean variability in δ13C, (ii) improved knowledge of the air-sea gas exchange coefficient, and (iii) a significant reduction in the uncertainty associated with the air-land biosphere disequilibrium.
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