Spatio-temporal distributions of air-sea fluxes of CO 2 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 air-sea 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 50ø S-20ø 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. Iarge-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 50øS-90ø S region only. Compared to observations made in 1992. seasonal sea surface fCO2 distribution is well reproduced. In the band 50ø S-20ø S. reconstructed sea surface fCO2 and climatological gas transtfert coefficient computed from derived climatological winds lead to an annual air-sea CO2 exchange between -0.20 and -0.37 Gt Carbon/year.