CO2 in the Weddell Gyre and Antarctic Circumpolar Current: austral autumn and early winter

Abstract

Quasi-continuous fugacity of CO 2 (fCO 2 ) data were collected in the eastern Weddell Gyre and southern Antarctic Circumpolar Current (ACC) of the Southern Ocean during austral autumn 1996. Full depth Total CO 2 (TCO 2 ) sections are presented for austral autumn and winter (1992) cruises. Pronounced fCO 2 gradients were observed at the Southern Ocean fronts. In the Weddell Gyre, fCO 2 regimes appeared to coincide with surface and subsurface hydrographic regimes. The southern ACC was supersaturated with respect to CO 2 , as was part of the northern Weddell Gyre. The southern Weddell Gyre was markedly undersaturated. The great potential of autumn cooling for generating undersaturation and CO 2 uptake from the atmosphere was demonstrated. In the northeastern Weddell Gyre, upwelling of CO 2 - and salt-rich deep water was shown to play a role as the horizontal fCO 2 distribution closely resembled that of the surface salinity. The total uptake of atmospheric CO 2 by the Weddell Gyre in autumn (45 days) was calculated to be 7·10 12 g C. The deep TCO 2 distribution noticeably reflected the different water masses in the region. A new deep TCO 2 maximum was detected in the ACC, which apparently characterizes the boundary between the equatorward flowing Antarctic Bottom Water (AABW) and the Circumpolar Deep Water (CDW). East of the Weddell Gyre, the AABW stratum is much thicker (>2000 m) than more to the west, on the prime meridian (<300 m).