Sea surface pCO2 and O2 in the Southern Ocean during the austral fall, 2008

The physical and biological processes controlling surface mixed layer pCO(2) and O-2 were evaluated using in situ sensors mounted on a Lagrangian drifter deployed in the Atlantic sector of the Southern Ocean (similar to 50 degrees S, similar to 37 degrees W) during the austral fall of 2008. The drifter was deployed three times during different phases of the study. The surface ocean pCO(2) was always less than atmospheric pCO(2) (-50.4 to -76.1 mu atm), and the ocean was a net sink for CO2 with fluxes averaging between 16.2 and 17.8 mmol C m(-2) d(-1). Vertical entrainment was the dominant process controlling mixed layer CO2, with fluxes that were 1.8 to 2.2 times greater than the gas exchange fluxes during the first two drifter deployments, and was 1.7 times greater during the third deployment. In contrast, during the first two deployments the surface mixed layer was always a source of O-2 to the atmosphere, and air-sea gas exchange was the dominant process occurring, with fluxes that were 2.0 to 4.1 times greater than the vertical entrainment flux. During the third deployment O-2 was near saturation the entire deployment and was a small source of O-2 to the atmosphere. Net community production (NCP) was low during this study, with mean fluxes of 3.2 to 6.4 mmol C m(-2) d(-1) during the first deployment and nondetectable (within uncertainty) in the third. During the second deployment the NCP was not separable from lateral advection. Overall, this study indicates that in the early fall the area is a significant sink for atmospheric CO2.