Structure of the Subtropical Front in the Tasman Sea

Abstract

The structure of the Subtropical Front (STF) in the southwest Pacific is established via a practical separation observed between the thermohaline properties of the subtropical and subantarctic waters (SAWs) converging at the STF. Previous examinations have been unable to separate waters in and about the STF zone, and could not identify the actual frontal interface of the STF, leaving its structure and properties largely unresolved. Consequently, other fronts in the area have been confused with the STF or misidentified. Away from the land boundaries of Australia and New Zealand, the STF appears as a well-defined zonal trending band, in which subtropical and SAWs over-ride, intrude, and interleave. The zone is bounded by quasi-parallel fronts, each associated with near definitive surface salinity values. The shallower northern front marks the equatorwards limits of surface SAW in the water column, and the deeper southern front represents the polewards limits of subsurface subtropical water (Tasman Sea Central Water). Empirical prescriptions used to approximately locate the STF over the last 70 years are explained and reconciled on comparison with the double frontal structure. Antarctic Intermediate Water (AAIW) at the STF also exhibits a double frontal structure, inside of which is maintained a pool of AAIW with distinctive properties. The AAIW frontal system forms a leaky barrier to northward movement of Southern Ocean AAIW in the eastern Tasman Sea.