Transformation of carbon and oxygen in the surface layer of the eastern Atlantic sector of the Southern Ocean

The biogeochemical transformation of carbon, and the exchange of carbon dioxide and oxygen over the sea–air interface were evaluated from measurements of dissolved inorganic carbon, total alkalinity, dissolved oxygen and nitrate in the Atlantic sector of the Southern Ocean. The investigation was carried out along longitude 6°E from December 1997 to January 1998 and was focused on three areas; the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and the Antarctic Polar Front (APF). The method is based on the assumption that differences between preformed and measured concentration of any property, are attributable to biological processes and sea–air exchange. By correcting the deficit of carbon and excess of oxygen observed in the surface mixed layer for the biological activity, the sea–air exchange of carbon dioxide and oxygen is estimated. In the SIE and the APF, a net release of carbon dioxide to the atmosphere of 0.1 and 0.5 mol m−2, respectively, was calculated over a time scale of several months (from austral winter to January). In the WIE a net oceanic uptake of carbon dioxide was calculated, with a sea–air exchange of −0.1 mol m−2. The calculated sea–air exchange of oxygen in the APF indicated an oceanic net release of oxygen to the atmosphere of 1.2 mol m−2. In the SIE and the WIE the sea–air exchange of oxygen was −0.3 and −1.4 mol m−2, respectively, from austral winter to January. Averaging the integrated sea–air exchanges indicated that the entire region acted as a weak oceanic source of carbon dioxide, from austral winter to January. The corresponding oxygen sea–air exchange showed a sink.