[1] We investigate the multidecadal and decadal trends in the flux of CO 2 between the atmosphere and the Southern Ocean using output from hindcast simulations of an ocean circulation model with embedded biogeochemistry. The simulations are run with NCEP-1 forcing under both preindustrial and historical atmospheric CO 2 concentrations so that we can separately analyze trends in the natural and anthropogenic CO 2 fluxes. We find that the Southern Ocean (<35°S) CO 2 sink has weakened by 0.1 Pg C a À1 from 1979-2004, relative to the expected sink from rising atmospheric CO 2 and fixed physical climate. Although the magnitude of this trend is in agreement with prior studie
