Air-sea CO.sub.2 flux in the Pacific Ocean for the period 1990--2009

• Published in: Biogeosciences 2014-02, Vol.11 (3), p.709
• Main Authors: Ishii, M, Feely, R. A, Rodgers, K. B, Park, G.-H, Wanninkhof, R, Sasano, D, Sugimoto, H, Cosca, C. E, Nakaoka, S, Telszewski, M, Nojiri, Y, Mikaloff Fletcher, S. E, Niwa, Y, Patra, P. K, Valsala, V, Nakano, H, Lima, I, Doney, S. C, Buitenhuis, E. T, Aumont, O, Dunne, J. P, Lenton, A, Takahashi, T
• Format: Article
• Language: English
• Subjects: Oceans; Southern oscillation
• ISSN: 1726-4170; 1726-4189

Air-sea CO.sub.2 fluxes over the Pacific Ocean are known to be characterized by coherent large-scale structures that reflect not only ocean subduction and upwelling patterns, but also the combined effects of wind-driven gas exchange and biology. On the largest scales, a large net CO.sub.2 influx into the extratropics is associated with a robust seasonal cycle, and a large net CO.sub.2 efflux from the tropics is associated with substantial interannual variability. In this work, we have synthesized estimates of the net air-sea CO.sub.2 flux from a variety of products, drawing upon a variety of approaches in three sub-basins of the Pacific Ocean, i.e., the North Pacific extratropics (18-66° N), the tropical Pacific (18° S-18° N), and the South Pacific extratropics (44.5-18° S). These approaches include those based on the measurements of CO.sub.2 partial pressure in surface seawater (pCO.sub.2 sw), inversions of ocean-interior CO.sub.2 data, forward ocean biogeochemistry models embedded in the ocean general circulation models (OBGCMs), a model with assimilation of pCO.sub.2 sw data, and inversions of atmospheric CO.sub.2 measurements. Long-term means, interannual variations and mean seasonal variations of the regionally integrated fluxes were compared in each of the sub-basins over the last two decades, spanning the period from 1990 through 2009. A simple average of the long-term mean fluxes obtained with surface water pCO.sub.2 diagnostics and those obtained with ocean-interior CO.sub.2 inversions are -0.47 ± 0.13 Pg C yr.sup.-1 in the North Pacific extratropics, +0.44 ± 0.14 Pg C yr.sup.-1 in the tropical Pacific, and -0.37 ± 0.08 Pg C yr.sup.-1 in the South Pacific extratropics, where positive fluxes are into the atmosphere. This suggests that approximately half of the CO.sub.2 taken up over the North and South Pacific extratropics is released back to the atmosphere from the tropical Pacific. These estimates of the regional fluxes are also supported by the estimates from OBGCMs after adding the riverine CO.sub.2 flux, i.e., -0.49 ± 0.02 Pg C yr.sup.-1 in the North Pacific extratropics, +0.41 ± 0.05 Pg C yr.sup.-1 in the tropical Pacific, and -0.39 ± 0.11 Pg C yr.sup.-1 in the South Pacific extratropics. The estimates from the atmospheric CO.sub.2 inversions show large variations amongst different inversion systems, but their median fluxes are consistent with the estimates from climatological pCO.sub.2 sw data and pCO.sub.2 sw diagnostics. In the South