New early winter fCO₂ data reveal continuous uptake of CO₂ by the Weddell Sea

Abstract

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_CO2 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 × 10¹³ gC y^-1 (≈ 2.4× 10^-3 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.