Variability of the Australian-Indonesian Monsoon during the Mid Pleistocene Transition (IODP 363 Site U1483)

The Australian-Indonesian Monsoon (AIM) extends across the equator to about 15°S and is characterized by the alternation of two main seasonal phases. In austral winter, easterly trade winds bring dry-cool conditions over the continent, while in summer westerly winds carry warm-humid air from the tropics into NW Australia. This monsoon system is highly variable and closely linked to regional and global scale changes in climate/ocean circulation, in particular El Nino-Southern Oscillation and the strength of the Walker and Hadley circulation, which strongly impact sea surface temperature (SST) in the Indo-Pacific Warm Pool. Recently, an extended, continuous sediment succession spanning the Mid Pleistocene Transition (MPT) was recovered at International Discovery Program (IODP) Site U1483 during Expedition 363 "Western Pacific Warm Pool". This key climatic event offers the opportunity to investigate the sensitivity of the AIM to changing mean-state background conditions, in particular ice volume, greenhouse gas concentrationsand the latitudinal thermal gradient. In this study, we analyze changes in radiolarian assemblages using a Modern Analogue Technique to reconstruct variations in winter SST and primary productivity across the MPT. We compare these results with XRF-scanner derived terrigenous runoff proxy records to investigate the dynamic coupling between the summer and winter components of the AIM. Preliminary results indicate that major changes in AIM dynamics (intensity and seasonality of precipitation and of upper ocean mixing by trade winds) occurred at ~1.6, ~1.2, ~0.9 and ~0.6 Ma and were linked to shifts in the position of the ITCZassociated with re-organization of the Hadley and Walker circulation.