Weddell Sea turned from source to sink for atmospheric CO2 between pre-industrial time and present

Using contemporary CO2 data from the subsurface Weddell Sea, the source/sink function of this region against the changing atmospheric CO2 level has been investigated. As in the central Weddell Sea, surface water is supplied by upwelling of subsurface water, the CO2 content is also forced by it. TCO2 data of four cruises were used to determine a robust value for the subsurface Warm Deep Water (WDW). After accounting for biological activity in the surface layer and salinity differences between the subsurface and surface waters, the forcing CO2 partial pressure (pCO(2)) was calculated from the TCO2 of the WDW and the conservative alkalinity as taken from the literature. As the WDW contains negligible anthropogenic CO2, the pCO(2) forcing by the WDW has been prevalent both in the pre-industrial and modem Weddell Sea. The calculated pCO(2) forcing amounts to 300-310 muatm at a minimum in late winter/early spring and possibly 30 muatm more during spring and summer. This figure does not represent the actual pCO(2), but rather the value before air-sea exchange gets effective. Hence, in pre-industrial times when the atmospheric pCO(2) was about 280 muatm, the Weddell Sea must have been a relatively strong source of atmospheric CO2. Because of the steadily rising atmospheric CO2 levels to more than the pCO(2) forcing by the WDW, the Weddell Sea turned into a CO, sink in recent times. The storage of anthropogenic CO2 in the Weddell Sea surface layer is estimated to be 4.1 Mol C m(-2). Applying the WDW forcing method to O-2, a steady state O-2 uptake from the atmosphere of 3.6 mol O-2 m(-2) year(-1) is computed. (C) 2003 Elsevier B.V. All rights reserved.