FY 2002

Air-sea fluxes of pre-industrial and anthropogenic CO₂ determined by inverse modeling of ocean carbon data

Gruber, N., M. Gloor, R.A. Feely, C. Roedenbeck, C.L. Sabine, and J.L. Sarmiento

In Sixth International Carbon Dioxide Conference, Sendai, Japan, 1–5 October 2001, 1039–1042 (2001)

We estimate the pre-industrial and anthropogenic CO fluxes across the air-sea interface on the basis of an ocean inverse modeling method that uses ocean interior observations of dissolved inorganic carbon (DIC) and associated anthropogenic CO estimates. The inversely estimated pre-industrial air-sea fluxes of CO reveal the expected pattern of CO uptake by the oceans in the mid to high latitudes and release back into the atmosphere in the low latitudes. By contrast, the air-sea flux of anthropogenic CO is found to be into the ocean everywhere, totaling about 1.8 Pg C yr. The present-day air-sea fluxes agree reasonably well with the flux estimates of Takahashi et al. (1999). A strong exception are the subpolar regions in the southern hemisphere (36°S-53°S), where Takahashi et al. estimate a net ocean uptake that is three to five times larger than our inversion estimates. Our smaller ocean uptake in the subpolar Southern hemisphere is in line, however, with recent atmospheric inverse modeling studies by TransCoM and a large number of ocean forward models run as part of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP). The inversion results show a modest cross-equatorial southward carbon transport in the Atlantic, and transport undistinguishable from zero in the other basins. Our inversely estimated pre-industrial air-sea CO fluxes nevertheless produce a significant interhemispheric gradient of atmospheric CO but this gradient is mainly a consequence of an interhemispheric asymmetry in the oceanic source-sink distribution interacting with atmospheric transport.