Spatio-temporal distributions of air-sea fluxes of CO₂ in the Indian and Antarctic oceans

Abstract

Sea surface and atmospheric measurements of carbon dioxide fugacity (fCO₂) made during 14 cruises in 1991, 1992 and 1993, are used to describe the seasonal and meridional variation of air-sea CO₂ flux into the antarctic, subantarctic, subtropical and tropical regions of the Indian Ocean. We first estimate seasonal (January to May and May to September) zonal averaged airsea CO₂ fluxes from shipboard measured sea surface and atmospheric fCO₂ as well as observed ship winds. Depending of the gas transfer coefficient used, a sink of – 0.22 or – 0.43 Gt Carbon from January to September is calculated for the band 50°S–20°S. From June to September, the tropical region is a source between 0.04 and 0.08 GtC. From January to May, the southern ocean is a sink between 0.01 and -0.03 GtC. Next, we compare these observed air-sea fluxes CO₂ calculations with reconstructed sea surface fCO₂ distributions obtained from climatological data (SST and wind). By using the in-situ data obtained in 1991, large-scale seasonal relations between sea surface fCO₂ and sea surface temperature (SST) are extracted and applied to the 1992 monthly climatological SST fields in the 50°S–20°S region only. Compared to observations made in 1992, seasonal sea surface fCO₂ distribution is well reproduced. In the band 50°S–20°S, reconstructed sea surface fCO₂ and climatological gas transfert coefficient computed from derived climatological winds lead to an annual air-sea CO₂ exchange between -0.20 and -0.37 Gt Carbon/year.