The amount of anthropogenic CO2 (Cant) that entered the Weddell Sea between 1992 and 2008 (Cant1992-2008) was assessed using the extended multiple linear regression (eMLR) method. In the Warm Deep Water (WDW) and the Weddell Sea Bottom Water (WSBW), Cant1992-2008 values were insignificant, whereas values as high as 8 μmol kg-1 were observed over the shelf. Cant1992-2008 concentrations in the surface layer varied with latitude between 2 and 11 μmol kg-1. Weak intrusion of anthropogenic CO2 into Weddell Sea Deep Water (WSDW) was demonstrated (C ant1992-2008 yields 1.5-2 μmol kg-1). That more Cant1992-2008 was found in the WSDW than in the WSBW is surprising, but can be explained by intense ventilation of the WSDW originating from east of the Weddell Gyre. The invasion of Cant1992-2008 provokes a shift in the equilibria of the carbonate system, resulting in acidification and reduction of CO32- concentration. The mean decrease of pH in the upper 200 m layer was 0.016. The largest decrease of calcite and aragonite saturation states was observed at the surface. This implies that surface waters might become undersaturated with respect to aragonite in the future while the underlying WDW is still saturated. Results of this analysis suggest that complete undersaturation of surface waters in the Weddell Sea will be reached after the 21st century. Copyright 2010 by the American Geophysical Union.