The Antarctic Ocean has been thought to be unimportant for the uptake of CO2 since upwelling of CO2-enriched deep waters would favour outgassing. Here we present the first direct f(CO)2 measurements obtained in early winter under the ice which, combined with estimated entrainment rates, show that the Weddell Sea, an area of intense upwelling manifested by the doming structure of the cyclonic gyre, has the capability to be almost continuously a sink for atmospheric CO2. A flux, effective after the ice cover disappears, is estimated to be -0.74±0.7 mmol m-2 d-1. Combined with a flux estimate in late autumn (-2.0 mmol m-2 d-1) integrated over the area of the central Weddell Gyre, a carbon uptake of 0.24 x 1013 gC y-1 (~2.4 x 1013 GtC y-1 being ~1‰ of global uptake) is computed, which is about a third of the strength of the biological pump of the Weddell Sea.