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Circumpolar transport in a quasigeostrophic Southern Ocean

Factors that determine the transport of a wind-driven model Antarctic Circumpolar Current (ACC) are considered. A simple theory is put forth to explain a saturation (transport becoming independent of forcing amplitude) seen for sufficiently strong forcing. The theory is based upon an old idea due to Stommel linking ACC transport to the basin-like (Sverdrup) flow to the north of channel latitudes. It differs from pervious Sverdrup theories of ACC transport in that the vertical structure of the flow plays a crucial role. Robustness of the results to factors such as the strength of a Rayleigh drag parameter and the relative strengths of the wind stress and wind stress curl is also considered. We also consider how simulations assuming realistic topography differ qualitatively from simulations where bottom topography takes the form of an idealised Guassian ridge. The main conclusion is that the `basin-like' dynamics in the region north of Drake Passage latitudes can have a profound influence on the eastward transport --- which is often assumed to be determined principally by channel-dynamics.