On the dynamics of wind-driven circumpolar currents

The factors controlling the transport of the Antarctic Circumpolar Current (ACC) have recently been a topic of heated debate. At the latitudes of Drak e Passage, potential vorticity contours are uninterrupted by coastlines, an d large amplitude flows are possible even with weak forcing and dissipation . The relationship between the dynamics of circumpolar currents and inertia l recirculations in closed basins is discussed. In previous studies, Sverdr up balance and baroclinic adjustment theories have both been proposed as th eories of the ACC transport. These theories predict the circumpolar transpo rt as various simple functions of the surface wind stress. A series of expe riments is performed with a simple channel model, with different wind stren gths and different idealized basin geometries, to investigate the relations hip between wind strength and circumpolar transport. The results show that baroclinic adjustment theories do predict transport in the special case of a periodic channel with no topographic variations, or when the wind forcing is very weak. More generally, the transport is determined by a complex int erplay between wind forcing, eddy fluxes, and topographic effects. There is no support for the idea that Sverdrup balance determines the transport thr ough Drake Passage.