Anthropogenic CO2 in Southern Ocean surface waters:: evidence from stable organic carbon isotopes

We present an approach for tracing the fate of anthropogenic CO2, compiling a large data set of stable organic carbon isotope ratios from surface sediments, plankton, and sinking matter in the Atlantic Ocean. The delta(13)C values of sinking matter are generally lower by 0.5-4.6 parts per thousand compared to the surface sediments. This difference increases with increasing latitude, which is explained by a stronger modern increase in surface water [CO2 (aq)] in the Southern Ocean relative to the Tropical/Subtropical Ocean. Preindustrial dissolved CO2 concentrations in Atlantic surface waters, estimated from the delta(13)C(org) of surface sediments, are compared to recently measured surface water [CO2 (aq)] values taken from literature. We obtain only a slight increase in [CO2 (aq)] at lower latitudes but a significant change of about 7 +/- 2 mu M in high latitudinal surface waters which we attribute to anthropogenic perturbation. Our results suggest that CO2 released by human activities has been stored in Southern Ocean surface waters.