Distribution of carbon dioxide partial pressure in surface waters of the Southwest Indian Ocean

Using data from different seasons (July 1984 and February — March 1985), we describe the geographical, annual, and seasonal variability of the partial pressure of carbon dioxide (pCO₂) in sea surface waters of the Southwest Indian Ocean. In Subtropical regions, we observed pCO₂ values almost 45 μatm higher in summer than in winter. This variation is produced principally by the seasonal change of sea surface water temperature. In contrast, in the Subantarctic region, pCO₂ values 25 μatm lower in summer than in winter in response to the predominant seasonal biological activity were observed. This characteristic phase change of the seasonal oceanic surface pCO₂ signal with latitude appears to be a global phenomenon and is mirrored in the northern hemisphere. A comparison with GEOSECS data shows good agreement between our total CO₂ profiles and the earlier observations. In the southern region of the Antarctic convergence, both the measured and calculated pCO₂ values agree with those of the GEOSECS program, and confirm that this region of the ocean is probably a source of CO₂ to the atmosphere throughout the year.