| The Leeuwin Current (LC), a deep and slender surface current, brings warms waters from the Pacific to the Indian Ocean through the Indonesian Throughflow (ITF) and results in a thermocline that can be weak or strong. The LC is stronger during the Austral winter (Pearce and Pattiaratchi, 1999) and conversely weak during the Austral summer due mostly to seasonal variations in wind stress. If the LC is weak, then cooler Sea Surface Temperature (SST) is present along the western shelf of Australia (Creswell and Golding, 1980). Australian climate is tightly linked to the position of the Leeuwin Current [and larger scale weather phenomena such as the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole, both of which are characterized by SST variations]. The impact of the LC on modern Australian climate provides an opportunity to evaluate climate in SW Australia in the Late Pleistocene.;Previous studies of the last 0.5 my indicate the LC was present north of the Northwest Cape, in both glacial and interglacial periods. This study presents a record from IODP Expedition 356 Site U1460 south of the Western Cape at in the northern Perth Basin. The goal of this study is to determine when the LC penetrated south of the Western Cape and its persistence through the late Pleistocene. Hemipelagic Site U1460 (27.4°S; 112.9°E; 214 m. w.d.) is under the influence of both the LC and the Western Australian Current (WAC) and impacted by strong westerly winds and associated winter rains. Benthic and planktonic foraminifera from the upper 50 meters were measured for stable isotope ratios of oxygen and carbon.;Variation in the benthic foramifera U. peregrina were used to determine the stratigraphy within the constraints of shipboard biostratigraphy. Temperatures were calculated from planktonic foraminiferal 18O and used to reconstruct the water column. Surface waters cooled during glacial periods suggesting either the Leeuwin Current did not reach south of the Northwest Cape then or was significantly cooler. The delta18O paleotemperatures for N. dutertrei and G. inflata, deeper-dwelling species, converge with surface water values, G. ruber , during glacial periods, suggesting a well-mixed thermocline. This may point to a strengthened WAC during glacial periods, although lower sea level may also have influenced thermocline development. |
