Vertical Eddy Fluxes in the Southern Ocean

The overturning circulation of the Southern Ocean has been investigated using eddying coupled ocean–sea ice models. The circulation is diagnosed in both density–latitude coordinates and in depth–density coordinates. Depth–density coordinates follow streamlines where the Antarctic Circumpolar Current is equivalent barotropic, capture the descent of Antarctic Bottom Water, follow density outcrops at the surface, and can be interpreted energetically. In density–latitude coordinates, wind-driven northward transport of light water and southward transport of dense water are compensated by standing meanders and to a lesser degree by transient eddies, consistent with previous results. In depth–density coordinates, however, wind-driven upwelling of dense water and downwelling of light water are compensated more strongly by transient eddy fluxes than fluxes because of standing meanders. Model realizations are discussed where the wind pattern of the southern annular mode is amplified. In density–latitude coordinates, meridional fluxes because of transient eddies can increase to counter changes in Ekman transport and decrease in response to changes in the standing meanders. In depth–density coordinates, vertical fluxes because of transient eddies directly counter changes in Ekman pumping.