Sensitivity of Australian monsoon to changing climate boundary conditions across the Mid-Pleistocene Transition

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The Australian Monsoon (AM) subsystem is a highly sensitive monitor of tropical hydroclimate variability, due to its location at the southern edge of the largest amplitude seasonal swing of the Intertropical Convergence Zone within the large-scale Asian-Australian monsoon system. However, the sensitivity of the AM to changing climate boundary conditions such as ice volume and greenhouse gas concentrations and the interhemispheric coupling with other monsoonal subsystems remain highly enigmatic due to our limited understanding of its past variability. During an IODP Expedition, an extended (sedimentation rate: ~10 cm/kyr), undisturbed Pleistocene hemipelagic sediment succession was retrieved for the first time off NW Australia (Site U1483, 13°5.24ʹS, 121°48.25ʹE, water depth: 1733 m). This carbonate- and clay-rich sequence provides an ideal archive to monitor the intensity and variability of the AM through different mean-states of Earth’s climate and to better constrain its sensitivity to changes in radiative forcing. Our project will focus on the Middle Pleistocene Transition (MPT, ~1.2-0.6 Ma), which registered fundamental changes, as Earth’s climate transitioned from an overall warmer phase with a reduced interhemispherical thermal contrast to a high-amplitude, quasi-periodic (~100 kyr) mode of glacial-interglacial variability. We will compare X-ray fluorescence (XRF) scanner derived terrigenous runoff (elemental ratios and accumulation rates) and paleoproductivity records (XRF-scanner derived biogenic silicon, carbon accumulation rates and carbon isotope gradients) in relation to temperature and ice volume variations (derived from foraminiferal oxygen isotopes and Mg/Ca). In combination with a high-resolution benthic oxygen isotope stratigraphy, the U1483 records of precipitation (altering salinity and terrigenous runoff during austral summer) and monsoonal wind (driving upwelling and productivity during austral winter) will shed light on the timing of major re-organizations in Southern Hemisphere tropical climate, linkages of high- and low-latitude climate change and the interhemispheric coupling of the AM with other monsoon subsystems. In particular, we will test the hypotheses that 1) humid conditions, characterized by year-round rainfall, prevailed in the warmer "41 kyr world", whereas rainfall seasonality increased with the emergence of high-amplitude, glacial-interglacial ~100 kyr cycles and that 2) major climate transitions at ~1.6, ~1.2, ~0.9 and ~0.6 Ma prior to and across the MPT coincided with changes in AM dynamics (intensity and seasonality of precipitation and of upper ocean convective mixing related to monsoonal winds).