Late Quaternary glacial-interglacial variability of the Indonesian Throughflow and Australian summer monsoon: Evidences from clay mineral and grain size records at IODP Site U1483 of northwest Australia

Abstract

Late Quaternary clay mineral assemblages, radiogenic isotope, and siliciclastic grain size records collected from high sedimentation Site U1483 of the International Ocean Discovery Program (IODP), beneath the path of the modern-day Indonesian Throughflow (ITF) and Leeuwin Current of northwest Australia are studied to reconstruct sediments provenance, transport processes and ocean current behavior, and to evaluate the Australian summer monsoon over the last 500 kyr. Clay minerals are primarily composed of smectite (41–70 %), followed by kaolinite (10–28 %), illite (13.5–25 %), and minor chlorite (3–14 %). Our reconstructed model based on the clay minerals source comparison and radiogenic isotope (Sr-Nd-Pb) records suggest the Victoria and Ord rivers of the Kimberley region as the source over the past 500 kyr for Site U1483. Smectite is mainly derived from the mafic volcanic and smectite-rich Bonaparte Gulf, whereas kaolinite and illite are primarily derived from felsic igneous and metamorphic rocks, respectively, found in the drainage areas of these rivers. Chlorite is primarily contributed by the Indonesian Throughflow (ITF), with a minor contribution from the northwest Australian rivers. Variations in the clay mineral assemblages and grain size records indicate strong glacial-interglacial cyclicity, with small grain size, high smectite, and low kaolinite and illite during glacial periods, while interglacial intervals are marked by a relative increase in kaolinite and illite, mean grain size, and decrease in smectite content. (Kaolinite+illite+chlorite)/smectite and kaolinite/smectite ratios are adopted as proxies for the ITF strength and Australian summer monsoon, respectively. High values of kaolinite/smectite and (kaolinite+illite+chlorite)/smectite ratios during the interglacial intervals indicate a wet summer monsoon with high river discharge and a strong ITF and Leeuwin Current, which has the capacity to transport a relatively high percentage of large-size kaolinite and illite sediments to Site U1483. In contrast, during glacials, the low values of kaolinite/smectite and (kaolinite+illite+chlorite)/smectite ratios imply a dry summer monsoon with low sediment discharge and weak ITF and Leeuwin Current, which can majorly carry the small smectite size particles in its suspension. The mean grain size and clay/silt ratio also indicate that the strength of ITF and Leeuwin Current was weak during glacials and gained high strength during the interglacials. The proxy records’ spectral analysis indicates a strong eccentricity period of 100-kyr, an obliquity period of 41-kyr, and a precession period of 23-kyr, implying that the clay mineral input along the northwest Australian margin is influenced by both high-latitude ice sheet forcing and low-latitude tropical processes.