Spatio-temporal variability of air–sea fluxes of carbon dioxide and oxygen in the Bransfield and Gerlache Straits during Austral summer 1995–96

The potential of the Bellingshausen Sea, Bransfield and Gerlache Straits as sinks for atmospheric CO2 was investigated by studying the carbon data obtained during FRUELA 95 (December 95–January 96) and FRUELA 96 (January–February 96) cruises. Air–sea exchange of CO2 and its relation to air–sea O2 fluxes, surface chlorophyll concentration, physical structures, and other environmental variables were also studied. The processes governing the temporal evolution of total inorganic carbon (TIC) between the two FRUELA cruises were assessed by means of a carbon budget. FRUELA 95 the frontal region associated with the Southern Boundary of the Antarctic Circumpolar Current (SbyACC) in the Bellingshausen Sea area presented high undersaturation of surface CO2 content (<200 μatm), in contrast to strong oxygen supersaturation (AOU<−48 μmol kg−1). This was accompanied by the development of a diatom bloom. Therefore, this area acted as a strong CO2 sink and oxygen source, −6.5±6 and 25±29 (mean±STD) mmol m−2 d−1, respectively. However, no phytoplanktonic biomass accumulation was reported for this area in late January 96 (FRUELA 96). The mean increase of 33 μatm in surface pCO2 between both surveys can be explained by seasonal warming and air–sea equilibration. On the other hand, in the Bransfield Strait area remnants of CO2-rich upwelled water caused it to act as a weak source of CO2 (1.3±1.1 mmol m−2 d−1) in early December 95. From this period to late January 96 increasing phytoplanktonic activity reduced surface pCO2 by 30 μatm, leading to a CO2 uptake of –0.9 mmol m−2 d−1. The Gerlache Strait had a mean flux of CO2 and O2 during both FRUELA cruises of –9.6 mmol m−2 d−1 and 19.9 mmol m−2 d−1, respectively. The carbon budget estimated for this area indicated biological processes as the main factor controlling temporal changes between both FRUELAs. Supporting this conclusion, the estimated carbon flux from the euphotic zone in this area was confirmed from measured sediment-trap data. icant linear correlations between air–sea CO2 and O2 fluxes were noted during periods of intensive phytoplanktonic activity during FRUELA 95 and in the Gerlache Strait during FRUELA 96.