Aridity record from the western Australia across the Early-Middle Pleistocene Transition

Australian aridity is primarily governed by large-scale atmospheric circulation and by the influence of the Australian-Indonesian monsoon (AIM). Regional climate variability is further modulated by coupled ocean-atmosphere modes, including the El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), and the Southern Annular Mode (SAM), whose interactions regulate moisture supply and hydroclimatic variability across the Australian continent. Western Australia has experienced pronounced hydroclimatic variability through time, characterized by arid glacial intervals and more humid interglacials, highlighting a strong regional sensitivity to insolation forcing, large-scale atmospheric circulation, and changes in Indo-Pacific climate modes. However, Australian hydroclimate responses during intervals of major climatic reorganization, such as the Early-Middle Pleistocene Transition (EMPT), remain poorly constrained. The EMPT (~1.2-0.6 Ma) marks a fundamental reorganization of the climate system, characterized by intensified glacial-interglacial cycles and a shift toward a ~100-kyr periodicity.

Here, we present a grain size record from IODP Site U1460 spanning the EMPT, reflecting changes in aridity within western Australia. Using a grain-size end-member unmixing model, we aim to distinguish relative changes in the proportions of fine-grained material and coarser-grained sediment as proxies for shifts between humid and arid intervals. Furthermore, we are developing a specialized method to remove biogenic silica from marine sediment, as the site contains a high concentration of sponge spicules. These spicules are particularly challenging to remove due to their chemical resilience. This method is critical to prevent interference with sedimentological measurements and to ensure the accuracy of our grain size end-member modelling and hydroclimatic interpretations. Our grain size record will not only provide a refined biogenic silica removal method but also offer new insights into the evolution of Australian arid environments and the mechanisms linking regional hydroclimate to global climate reorganization during the Pleistocene. These findings will serve as critical analogues for understanding hydroclimatic sensitivity under sustained anthropogenic forcing.