Northern boundary currents and adjacent recirculations off southwestern Australia



Full-depth hydrographic and velocity measurements along 115°E south of Australia (WHP section I9S) reveal an active northern boundary current regime within 200–300 km of the Australian continental shelf and an offshore recirculation regime within the South Australian Basin. In the upper ocean an oft-described westward-flowing northern boundary current, the Flinders Current, extends through the thermocline and the salinity minimum strata of Antarctic Intermediate Water, with an opposing eastward recirculation to its south. The new data shows that beneath the Flinders Current, an eastward-flowing deep northern boundary current transports water of subtropical Indian Ocean origin supplied by southward deep flow along the western continental slope of Australia in the Perth Basin. Between these northern boundary currents and the Antarctic Circumpolar Current, thermocline and deep geostrophic shears indicate weak recirculations, eastward at thermocline levels and westward in the deep water. Lowered Acoustic Doppler current profiler data reveal stronger organized recirculations to both the Flinders Current and the deep northern boundary current, with the westward deep recirculation exceeding the eastward transport of the deep northern boundary current and thus representing a net supply of deep water to the Perth Basin.