Figure 4: Air–sea fluxes over the Southern Ocean.

a, The mean zonal wind stress, τ_x (see colour scale) for the period 1980–2000 from the National Centers for Environmental Prediction (NCEP) reanalysis. Subantarctic and polar fronts are marked in orange as in Fig. 2. The winter ice edge is marked by the black line and the 27.6 kg m⁻³ outcrop by the white line. b, The National Centers for Environmental Predication mean net (radiative+sensible+latent) air–sea heat flux for the same period, including contributions from evaporation and precipitation expressed as a pseudo-heat flux. Blue indicates regions where the heat flux is out of the ocean, and yellow–orange represents regions where it is directed into the ocean. As in a, the black and white lines mark the position of the winter ice edge and the 27.6 kg m⁻³ outcrop. c, An estimate of the freshwater flux contribution from sea-ice manufacture and export: red shading indicates buoyancy gain by the ocean and blue shading indicates buoyancy loss. The position of the summer and winter sea-ice edge is marked in black. The area within the summer ice edge is shaded in white. The subantarctic and polar front positions are again marked in orange. Data sources and methods are described by Li and colleagues¹⁰¹. d, Circumpolar zonal average of temperature (T) and salinity (S) (scales on right) from the CARS2209 atlas (courtesy of the Commonwealth Scientific and Industrial Research Organisation) with density contoured in black. The vertical white lines indicate the thickness of the density layers. The black arrow marks the sense of the eddy-induced upwelling.