Late Pleistocene Leeuwin Current Variability: Multi-Species Foraminiferal Isotope Records from IODP Site U1460, SW Australian Shelf

Australian climate, drought and precipitation, is tightly linked to the position of the Leeuwin Current (LC) and larger scale weather phenomena such as ENSO and the Indian Ocean Dipole, both of which are characterized by sea surface temperature (SST) variations. If the LC is weak, then cooler SST are present along the western shelf and a negative-like phase of IOD on Australia results in drought (Saji et al. 2009). Previous studies of the last 0.5 Myr indicate the LC was present north of the Western Cape, in both glacial and interglacial periods. This study presents a record from south of the Western Cape at IODP Expedition 356 Site U1460 in the northern Perth Basin. 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. Samples were taken at 1.5 m intervals from cores 1F-57F (0-267m), washed (63 µm) and picked for planktonic (G. sacculifer, G. ruber, G. inflata, N. dutertrei) and benthic (Cibicides spp. and U. peregrina) foraminiferal species. Stable isotopes were measured at MARUM, Bremen University using a Finnigan MAT 251 mass spectrometer with a Kiel device, and corrected for species-specific disequilibrium effects. The δ18O values are interpreted as temperature (Spooner et al., 2011); ages are constrained by shipboard biostratigraphy. The surface waters cooled during glacial periods suggesting the Leeuwin Current did not reach south of the Western Cape, or was significantly cooler. The δ18O signals for N. dutertrei and G. inflata, deeper-dwelling species, converge with surface water values during glacial periods, suggesting a deeper thermocline. This may point to a strengthened WAC during glacial periods, although lower sea level may also have influenced thermocline development. The impact of the LC on modern Australian climate provides an opportunity to evaluate climate in SW Australia in the Late Pleistocene. Spooner, M.I., De Deckker, P., Barrows, T.T., Fifield, L.K., 2011. The behaviour of the Leeuwin Current offshore NW Australia during the last five glacial-interglacial cycles. Glob. Planet. Change 75, 119e132. Saji N.H., Goswami B.N., Vinayachandran P.N., Yamagata T., 1999: A dipole mode in the tropical Indian Ocean, Nature, 401, 360-363.