The Bass Strait water cascade during summer 1981–1982

Abstract

Water in Bass Strait, a shallow extension of the Australian shelf between the Great Australian Bight and the Tasman Sea, is denser than Tasman Sea surface water in winter but of comparable density in summer. Winter downflow of denser water creates high-salinity intrusions along the continental slope, which are carried northward in a narrow undercurrent at 300–400 m depth. This paper gives a detailed description of the summer situation based on cruise data from November 1981. It is found that no downflow from Bass Strait occurred during the cruise. Parcels, intrusions, and filaments of Bass Strait Water were found along the continental slope in the Tasman Sea over a large area. They are interpreted as remnants from the winter downflow. The two-fold structure of the Cascade known from winter observations, with downflow at two closely adjacent but distinctly different density levels, was clearly reflected in the data. Contrary to the winter situation, parcels of Bass Strait Water were found both north and south of the Cascade and both close to, and at distance from, the continental shelf. This suggests that the northward undercurrent may not exist in summer.