Estimates of anthropogenic carbon in the Indian Ocean with allowance for mixing and time-varying air-sea CO2 disequilibrium

[1] We apply to the Indian Ocean a novel technique to estimate the distribution, total mass, and net air-sea flux of anthropogenic carbon. Chlorofluorocarbon data are used to constrain distributions of transit times from the surface to the interior that are constructed to accommodate a range of mixing scenarios, from no mixing ( pure bulk advection) to strong mixing. The transit time distributions are then used to propagate to the interior the surface water history of anthropogenic carbon estimated in a way that includes temporal variation in CO2 air-sea disequilibrium. By allowing for mixing in transport and for variable air- sea disequilibrium, we remove two sources of positive bias common in other studies. We estimate that the anthropogenic carbon mass in the Indian Ocean was 14.3 - 20.5 Gt in 2000, and the net air- sea flux was 0.26 - 0.36 Gt/yr. The upper bound of this range, the no-mixing limit, generally coincides with previous studies, while the lower bound, the strong-mixing limit, is significantly below previous studies.