The role of eddies in a laboratory study of the Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) is an eastward flowing current that transports on average 134 Sv around the Southern Ocean, dominating the dynamics of the region. Westerly winds drive the ACC, which roughly follows the path of the maximum westerlies at this latitude, as well as a geostrophic flow component set up by the presence of the Antarctic Polar Front (APF). The APF, characterized by strong density gradients, releases potential energy through baroclinic instabilities that cast off eddies poleward. We investigate the behavior of these instabilities, or eddies, in a laboratory setting by reproducing an idealized ACC system through a combination of mechanical and buoyancy forcing applied in a rotating cylindrical tank. We find that the eddies generated by the baroclinic instability of the buoyant current are important in setting the final stratification of the circumpolar front by determining the depth of penetration and strength of the current at equilibrium. We discuss the implications of our laboratory findings for understanding those processes that contribute to setting the stratification and transport in the ACC.