The behaviour of the Leeuwin Current offshore NW Australia during the last five glacial-interglacial cycles

The Leeuwin Current is an anomalous eastern boundary current along the western Australian coast. To investigate its behaviour through time, we studied core MD002361 obtained from below the present-day pathway of the Leeuwin Current offshore the NW tip of Western Australia. Planktonic foraminifera assemblages, sea-surface temperature estimates reconstructed from those assemblages, together with the δ¹⁸O and δ¹³C signals of near-surface dwelling foraminifera (Globigerinoides ruber), were used to reconstruct the vertical structure of the water column for the past 500ka. Our findings indicate that the Leeuwin Current was present along the western coastline of Australia even during glacial periods. During those times, there was a greater influence of South Indian Subtropical Water (STW) and South Indian Central Water (SICW) due to a 3-4° northward migration of the Indonesian Throughflow Water/South Indian Central Water frontal system. This resulted in an overall 6-9°C decrease in SST, paralleled by a thickening and greater homogeneity of the mixed layer. The increased influence of STW and SICW also suggests that the West Australian Current, which presently sits below the Leeuwin Current, was strengthened during the glacial periods and contributed to a weakening of the Leeuwin Current. Conversely, the Leeuwin Current was 'stronger' during interglacial periods due to a thicker component of Indonesian Throughflow Water sourced from the Indo Pacific Warm Pool. This was particularly the case during marine isotope stage 5.5 (MIS) and the 'super' interglacial MIS 11.