The dynamical balance, transport and circulation of the Antarctic Circumpolar Current

TLDR

The Antarctic Circumpolar Current’s circulation is reviewed, illustrated by recent WOCE observations, highlighting the interplay of zonal momentum balance, meridional circulation, diapycnal mixing, and eddy processes. The study aims to elucidate how wind stress and surface buoyancy flux drive the ACC’s dynamical balance and meridional circulation, and to introduce new models linking these forcings to ACC transport and Southern Ocean overturning. The authors analyze form stress on tilted isopycnals and the ocean bottom as key momentum‑balance mechanisms, and develop models that relate wind stress, buoyancy flux, diapycnal mixing, and eddy processes to ACC transport and Southern Ocean overturning. They show that the Sverdrup balance fails in the ACC, with geostrophic contours playing a crucial role in vorticity balance.

Abstract

The physical elements of the circulation of the Antarctic Circumpolar Current (ACC) are reviewed. A picture of the circulation is sketched by means of recent observations from the WOCE decade. We present and discuss the role of forcing functions (wind stress, surface buoyancy flux) in the dynamical balance of the flow and in the meridional circulation and study their relation to the ACC transport. The physics of form stress at tilted isopycnals and at the ocean bottom are elucidated as central mechanisms in the momentum balance. We explain the failure of the Sverdrup balance in the ACC circulation and highlight the role of geostrophic contours in the balance of vorticity. Emphasis is on the interrelation of the zonal momentum balance and the meridional circulation, the importance of diapycnal mixing and eddy processes. Finally, new model concepts are described: a model of the ACC transport dependence on wind stress and buoyancy flux, based on linear wave theory; and a model of the meridional overturning and the mean density structure of the Southern Ocean, based on zonally averaged dynamics and thermodynamics with eddy parametrization.