Southern hemisphere ocean CO₂ uptake: reconciling atmospheric and oceanic estimates

Abstract

Using an atmospheric inversion model we investigate the southern hemisphere ocean CO₂ uptake. From sensitivity studies that varied both the initial ocean flux distribution and the atmospheric data used in the inversion, our inversion predicted a total (ocean and land) uptake of 1.65–1.90 Gt C yr⁻¹. We assess the consistency between the mean southern hemisphere ocean uptake predicted by an atmospheric inversion model for the 1991–1997 period and the T99 ocean flux estimate based on observed ΔpCO₂ in Takahashi et al. (2002; Deep-Sea Res II, 49, 1601–1622). The inversion can not match the large 1.8 Gt C yr⁻¹ southern extratropical (20–90°S) uptake of the T99 ocean flux estimate without producing either unreasonable land fluxes in the southern mid-latitudes or by increasing the mismatches between observed and simulated atmospheric CO₂ data. The southern extratropical uptake is redistributed between the mid and high latitudes. Our results suggest that the T99 estimate of the Southern Ocean uptake south of 50°S is too large, and that the discrepancy reflects the inadequate representation of wintertime conditions in the T99 estimate.