[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P17] Glacial–interglacial variations in the Leeuwin Current for the last 50,000 years based on Nd isotope records of benthic foraminifers

*Ryota Wako¹, Hideko Takayanagi¹, Shigeyuki Wakaki², Takeshige Ishiwa⁴, Yusuke Yokoyama⁵, Hitomi Uchimura Wakaki³, Tsuyoshi Ishikawa², Yasufumi Iryu¹ (1.Department of earth science, Tohoku university , 2.Kochi Institute for Core Sample Research, JAMSTEC, 3.Center for Advanced Marine Core Research, Kochi University, 4.National Institute of Polar Research, 5.Atmosphere and Ocean Research Institute, University of Tokyo)

Keywords:Neodymium isotope composition, Leeuwin Current, Benthic foraminifera, Glacial-interglacial, Paleoenvironment, IODP

The Leeuwin Current (LC) is a major warm current flowing poleward from the equatorial region along the west coast of Australia. Variations in the air-sea interaction in its surrounding area (e.g., ENSO and wind strength) and the intensity of the Australian monsoon are known to have a strong influence on the strength and pathway of the LC at the seasonal to interannual time scales. However, it is still controversial how the LC responded to paleoclimate and paleoceanographic conditions at the millennial or longer time scales, such as glacial-interglacial climate changes. In this study, we analyzed neodymium (Nd) isotope composition (εNd) of bulk benthic foraminifers from shallow-water to hemipelagic carbonate sediment cores (IODP Exp. 356 sites U1460, U1461, and U1463 from south to north) collected off West Australia to understand water mass exchanges and variations in the strength and pathway of the LC for the last 50,000 years.
Nd isotope results indicate that the coastal current, which flows the surface between the LC and Australian continent, became predominant at least in coastal areas around U1461 in the latest Pleistocene. This may indicate that the pathway of the LC moved slightly offshore at northwestern Australia due to the stronger Australian monsoon and/or thickening of surface to sub-surface water masses during the postglacial period. While, during the last glacial maximum (MIS2), the εNd composition of all sites exhibited more radiogenic values than those of the postglacial period. Our results suggest that, although the εNd values of the studied cores were affected by sea-level changes, the LC region was predominantly influenced by Pacific-origin waters flowing into the Indian Ocean from the northern and southern Pacific Ocean through the Indonesian Through Flow even during the last glacial period.