The Indonesian Throughflow regulated Australian summer monsoon across the Mid-Brunhes Event

The Mid-Brunhes Event (MBE; at ∼450 ka) represents a global climate shift associated with warmer conditions, higher sea levels and smaller ice volume during the interglacials since Marine Isotope Stage (MIS) 11 and is of critical importance for comprehending global climate dynamics. To date, the sensitivity of the Indonesian Throughflow (ITF) and the Asian-Australian monsoon dynamics to changing MBE climate have not been well documented. Here, we investigated clay mineral, grain size and radiogenic isotopic records of the International Ocean Discovery Program (IODP) Site U1483 from the eastern Indian Ocean off northwest Australia over the last 795 kyr. This study provides crucial insights into the sediment source, long-term variability of the ITF and its influence on the Australian summer monsoon and the oceanic and atmospheric systems interplay across the MBE. Clay minerals and Sr-Nd-Pb isotopes suggest that the sediments of Site U1483 are primarily from the Kimberley region of northwest Australia with minor contributions from the Timor region carried by the ITF. Kaolinite/smectite ratio coupled with mean grain size were adopted to indicate variability in the intensity of the ITF and Australian monsoon. High values of kaolinite/smectite and mean grain size during interglacials indicate a strong ITF, which may have contributed to maintaining the humid Australian summer monsoon with high river discharge over the last 795 kyr. In contrast, low values imply a weak ITF, which might have been one of the major amplifying factors resulting in dry conditions over northwest Australia during glacials. Spectral and wavelet analyses of the proxy records display the concentration of power on 100-kyr, 41-kyr and 23-kyr bands, implying jointly effects of sea level variations associated with the global ice volume and expansion/contraction of the Intertropical Convergence Zone on the paleoclimate and clay minerals sedimentation along northwest Australia. The long-term variations of clay minerals, grain size and their relevant proxy records from Site U1483 display a remarkable shift at an earlier stage of MIS 12, coinciding with the MBE. We attribute this shift to the submergence of sediment source areas and enhanced ITF due to sea-level rise in recent interglacials. Our findings provide insights into the line of evidence that the ITF and Australian monsoon became increasingly forced by the global sea level change and the MBE was a global phenomenon influencing both the monsoonal and oceanic systems. • NW Australian rivers and to a minor extent the Timor region contributed clay minerals to the NW Australian shelf. • The ITF regulated the Australian summer monsoon during glacial-interglacial cycles. • The Mid-Brunhes Event resulted in intensification of the ITF due to sea-level rise along northwest Australia.