Revised budget for the oceanic uptake of anthropogenic carbon dioxide
Tracer-calibrated models of the total uptake of anthropogenic CO 2 by the world's oceans give estimates of about 2 gigatonnes carbon per year 1 , significantly larger than a recent estimate 2 of 0.3-0.8 Gt C yr -1 for the synoptic air-to-sea CO 2 influx. Although both estimates require that the global CO 2 budget must be balanced by a large unknown terrestrial sink, the latter estimate implies a much larger terrestrial sink, and challenges the ocean model calculations on which previous CO 2 budgets were based. The discrepancy is due in part to the net flux of carbon to the ocean by rivers and rain, which must be added to the synoptic air-to-sea CO 2 flux to obtain the total oceanic uptake of anthropogenic CO 2 . Here we estimate the magnitude of this correction and of several other recently proposed adjustments to the synoptic air-sea CO 2 exchange. These combined adjustments minimize the apparent inconsistency, and restore estimates of the terrestrial sink to values implied by the modelled oceanic uptake.