Surface water carbon dioxide in the southwest Indian sector of the Southern Ocean: a highly variable CO2 source/sink region in summer

Measurements of partial pressure of carbon dioxide (pCO₂), total dissolved inorganic carbon (TCO₂), total alkalinity (TA) and chlorophyll a (Chl a) have been made in surface water in the southwestern Indian sector of the Southern Ocean (20–85°E) in the austral summer (INDIVAT V cruise, January-February 1987). Between Antarctica and Africa, pCO₂ distribution was linked to the oceanic frontal zones and Chi a variations. The pCO₂ spatial structure was very close to that explored in summer 1967 in the same region but the pCO₂ differences between the ocean and the atmosphere were smaller in 1987 than 20 years ago. At all latitudes we found strongly contrasting surface pCO₂ characteristics between eastern (around 80°E) and western (around 25°E) regions; C02 sources were mainly in the west and CO₂ sinks in the east. South of 60°S, the contrast could be due to biological activity. Between 60°S and the Antarctic Polar Front, intensification of upwelling might be responsible for the higher _pCO₂ values in the west.