Changes in the 13C/12C of dissolved inorganic carbon in the ocean as a tracer of anthropogenic CO2 uptake -: art. no. 1004

[1] Measurements of the delta(13)C of dissolved inorganic carbon primarily during World Ocean Circulation Experiment and the Ocean Atmosphere Carbon Exchange Study cruises in the 1990s are used to determine ocean-wide changes in the delta(13)C that have occurred due to uptake of anthropogenic CO2. This new ocean-wide delta(13)C data set (similar to25,000 measurements) substantially improves the usefulness of delta(13)C as a tracer of the anthropogenic CO2 perturbation. The global mean delta(13)C change in the surface ocean is estimated at -0.16 +/- 0.02parts per thousand per decade between the 1970s and 1990s with the greatest changes observed in the subtropics and the smallest changes in the polar and southern oceans. The global mean air-sea delta(13)C disequilibrium in 1995 is estimated at 0.60 +/- 0.10parts per thousand with basin-wide disequilibrium values of 0.73, 0.63, and 0.23parts per thousand for the Pacific, Atlantic, and Indian oceans, respectively. The global mean depth-integrated anthropogenic change in delta(13)C between the 1970s and 1990s was estimated at -65 +/- 33parts per thousand m per decade. These new estimates of air-sea delta(13)C disequilibrium and depth-integrated delta(13)C changes yield an oceanic CO2 uptake rate of 1.5 +/- 0.6 Gt C yr(-1) between 1970 and 1990 based on the atmospheric CO2 and (CO2)-C-13 budget approaches of Quay et al. [1992] and Tans et al. [1993] and the dynamic method of Heimann and Maier-Reimer [1996]. Box-diffusion model simulations of the oceanic uptake of anthropogenic CO2 and its delta(13)C perturbation indicate that a CO2 uptake rate of 1.9 +/- 0.4 Gt C yr(-1) (1970-1990) explains both the observed surface ocean and depth-integrated delta(13)C changes. Constraining a box diffusion ocean model to match both the observed delta(13)C and bomb C-14 changes yields an oceanic CO2 uptake rate of 1.7 +/- 0.2 Gt C yr(-1) (1970-1990). The oceanic CO2 uptake rates derived from anthropogenic changes in ocean delta(13)C are similar to rates determined by atmospheric CO2 and O-2 budgets [Battle et al., 2000], atmospheric delta(13)C and CO2 measurements [Ciais et al., 1995], and GCM simulations [Orr et al., 2001].