Air‐sea exchange of carbon dioxide in the Southern Ocean and Antarctic marginal ice zone

Abstract Direct carbon dioxide flux measurements using eddy covariance from an icebreaker in the high‐latitude Southern Ocean and Antarctic marginal ice zone are reported. Fluxes were combined with the measured water‐air carbon dioxide partial pressure difference (Δ p CO 2 ) to compute the air‐sea gas transfer velocity ( k , normalized to Schmidt number 660). The open water data showed a quadratic relationship between k (cm h −1 ) and the neutral 10 m wind speed ( U 10 n , m s −1 ), k open = 0.245 U 10 n 2 + 1.3, in close agreement with decades old tracer‐based results and much lower than cubic relationships inferred from previous open ocean eddy covariance studies. In the marginal ice zone, the effective gas transfer velocity decreased in proportion to sea ice cover, in contrast with predictions of enhanced gas exchange in the presence of sea ice. The combined open water and marginal ice zone results affect the calculated magnitude and spatial distribution of Southern Ocean carbon flux.