This project will develop a delta13C-based approach for separating the roles of air-sea CO2 exchange and ocean circulation as controls on the uptake and distribution of anthropogenic CO2 to the global ocean. First it will determine anthropogenic CO2 uptake rates in the S. Atlantic, Pacific and Indian Oceans as the Repeat Hydrography delta13C data become available. Second, it will compare the measured anthropogenic delta13C and DIC changes with predictions from ocean GCMs. It determine the relative contributions that air-sea exchange and large-scale transport make towards the anthropogenic CO2 accumulation in each ocean basin based on the measured delta13C change and air-sea delta13C disequilibrium. The modeling efforts will focus on determining whether the regional uptake characteristics of GCMs are realistic as compared to observations, with the overall goal of identifying strategies for using data constraints to evaluate model skill in simulating regional ocean CO2 uptake.