Eddy Fluxes and Jet-Scale Overturning Circulations in the Southern Ocean

The relationship between the Antarctic Circumpolar Current (ACC) jets and eddy heat and momentum fluxes is investigated using an eddy-resolving model. In ocean sectors where the jets are relatively well defined, there exist jet-scale overturning circulations where sinking motion is located on the equatorward, and rising motion on the poleward flank of the jets. For the 125°E-145°E sector where jets are especially zonal, a spatial and temporal decomposition of eddy heat and momentum fluxes reveals that transient eddies are baroclinic, and act to accelerate the jet with a maximum of eddy momentum flux convergence at its center, but to decelerate the zonal current at the critical latitude along the jet flanks. In contrast to eddy heat flux that drives large-scale overturning circulation encompassing multiple jets, eddy momentum flux is smaller in scale and responsible for the jet-scale overturning circulations. Within these small-scale overturning circulations, the sinking motion is closely associated with the mixed layer, suggesting that in the Southern Ocean, the eddy-driven jet-scale overturning circulation may play an important role for the formation of the mixed layer. The possible role of this overturning circulation on the vertical transport of the zonal momentum is also discussed.