A circulation model of the abyssal Tasman Sea

Abstract

A primitive equation shallow-water model with idealized topography has been used to investigate the dynamics of the abyssal Tasman Sea. The questions addressed relate to the influence of topography on the circulation pattern and the forcing mechanisms. Circulations driven by both inflow of Deep Antarctic Circumpolar Current water and East Australian Current eddies have been considered. The former usually results in upwelling that drives cyclonic flow throughout the basin. Strong flow is mainly restricted to regions of sharp potential vorticity gradients such as the continental rise, while flow over the abyssal plain is generally much weaker. Simulated East Australian Current eddies propagate their influence through Rossby wave generation. Over the abyssal plain, potential vorticity gradients are weak and the resulting low energy waves have little effect on the wider circulation. Eddies over the continental rise are more efficient at generating longer waves which can propagate large distance along geostrophic contours. Those generated in the west (East Australian rise) tend to be strongly scattered by blocked geostrophic contours to the north, resulting in enhanced dissipation and very limited mean flow generation. However, those generated in the east (Lord Howe Rise) propagate into the basin interior and generate strong mean flows along geostrophic contours. The model results suggest that Circumpolar Current forcing can most easily account for available observations.