Meridional transport of dissolved inorganic carbon in the South Atlantic Ocean


J. Holfort, , K.M. Johnson, B. Schneider, G. Siedler, and D.W.R. Wallace


The meridional oceanic transports of dissolved inorganic carbon and oxygen were calculated using six transoceanic sections occupied in the South Atlantic between 11°S and 30°S. The total dissolved inorganic carbon (TCO2) data were interpolated onto conductivity-temperature-depth data to obtain a high-resolution data set, and Ekman, depth-dependent and depth-independent components of the transport were estimated. Uncertainties in the depth-independent velocity distribution were reduced using an inverse model. The inorganic carbon transport between 11°S and 30°S was southward, decreased slightly toward the south, and was -2150±200 kmol s-1 (-0.81±0.08 Gt C yr-1) at 20°S. This estimate includes the contribution of net mass transport required to balance the salt transport through Bering Strait. Anthropogenic CO2 concentrations were estimated for the sections. The meridional transport of anthropogenic CO2 was northward, increased toward the north, and was 430 kmol s-1 (0.16 Gt C yr-1) at 20 °S. The calculations imply net southward inorganic carbon transport of 2580 kmol s-1 (1 Gt C yr-1) during preindustrial times. The slight contemporary convergence of inorganic carbon between 10°S and 30°S is balanced by storage of anthropogenic CO2 and a sea-to-air flux implying little local divergence of the organic carbon transport. During the preindustrial era, there was significant regional convergence of both inorganic carbon and oxygen, consistent with a sea-to-air gas flux driven by warming. The northward transport of anthropogenic CO2 carried by the meridional overturning circulation represents an important source for anthropogenic CO2 currently being stored within the North Atlantic Ocean.