Ocean circulation in the Great Australian Bight in an eddy-resolving ocean reanalysis: The eddy field, seasonal and interannual variability

Abstract

The ocean circulation in the Great Australian Bight (GAB) is dominated by the surface-intensified Leeuwin Current (LC) over the outer continental shelf, and the Flinders Current farther offshore. In the GAB, the LC flows eastwards and varies seasonally, with strongest currents of up to 0.8 m/s (at 130.5°E), bringing warm and salty waters as far east as western Tasmania. The Flinders Current flows westwards, as an undercurrent at depths of around 500 m over the continental slope and at the surface offshore of the LC. Off the shelf, the GAB is rich in mesoscale eddies, with surface-intensified currents of up to 0.4 m/s that are coherent over the full water depth (getting weaker with depth). Within deep-water eddies, isotherms are displaced vertically by up to 200 m. Eddies in the eastern GAB are most energetic in austral winter and spring - coincident with the seasonal weakening of the LC. The eastern-most “penetration” of GAB eddies occurs in austral winter - when the LC starts to weaken. We hypothesise that the horizontal shear associated with the LC generates eddies in the eastern GAB. The volume transport of the LC at the head of the GAB is typically between 1 and 7 Sv, with a clear seasonal cycle, and the interannual variability of LC transport is up to 2 Sv.