Changes in the super(13)C/ super(12)C of dissolved inorganic carbon in the ocean as a tracer of anthropogenic CO sub(2) uptake

Measurements of the delta super(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 super(13)C that have occurred due to uptake of anthropogenic CO sub(2). This new ocean-wide delta super(13)C data set (~25,000 measurements) substantially improves the usefulness of delta super(13)C as a tracer of the anthropogenic CO sub(2) perturbation. The global mean delta super(13)C change in the surface ocean is estimated at-0.16 plus or minus 0.02ppt 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 super(13)C disequilibrium in 1995 is estimated at 0.60 plus or minus 0.10ppt with basin-wide disequilibrium values of 0.73, 0.63, and 0.23ppt for the Pacific, Atlantic, and Indian oceans, respectively. The global mean depth-integrated anthropogenic change in delta super(13)C between the 1970s and 1990s was estimated at-65 plus or minus 33ppt m per decade. These new estimates of air-sea delta super(13)C disequilibrium and depth- integrated delta super(13)C changes yield an oceanic CO sub(2) uptake rate of 1.5 plus or minus 0.6 Gt C yr super(-1) between 1970 and 1990 based on the atmospheric CO sub(2) and super(13)CO sub(2) 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 CO sub(2) and its delta super(13)C perturbation indicate that a CO sub(2) uptake rate of 1.9 plus or minus 0.4 Gt C yr super(-1) (1970-1990) explains both the observed surface ocean and depth- integrated delta super(13)C changes. Constraining a box diffusion ocean model to match both the observed delta super(13)C and bomb super(14)C changes yields an oceanic CO sub(2) uptake rate of 1.7 plus or minus 0.2 Gt C yr super(-1) (1970-1990). The oceanic CO sub(2) uptake rates derived from anthropogenic changes in ocean delta super(13)C are similar to rates determined by atmospheric CO sub(2) and O sub(2) budgets [Battle et al. 2000], atmospheric delta super(13)C and CO sub(2) measurements [Ciais et al. 1995], and GCM simulations [Orr et al. 2001].