Middle Pleistocene re-organization of Australian Monsoon

The sensitivity of the Australian Monsoon to changing climate boundary conditions remains controversial due to limited understanding of forcing processes and past variability. Here, we reconstruct austral summer monsoonal discharge and wind-driven winter productivity across the Middle Pleistocene Transition (MPT) in a sediment sequence drilled off NW Australia. We show that monsoonal precipitation and runoff primarily responded to precessional insolation forcing until similar to 0.95 Ma, but exhibited heightened sensitivity to ice volume and rho CO2 related feedbacks following intensification of glacial-interglacial cycles. Our records further suggest that summer monsoon variability at the precessional band was closely tied to the thermal evolution of the Indo-Pacific Warm Pool and strength of the Walker circulation over the past similar to 1.6 Myr. By contrast, productivity proxy records consistently tracked glacial-interglacial variability, reflecting changing rhythms in polar ice fluctuations and Hadley circulation strength. We conclude that the Australian Monsoon underwent a major re-organization across the MPT and that extratropical feedbacks were instrumental in driving short- and long-term variability.

Automated summary

The sensitivity of the Australian Monsoon to changing climate boundary conditions remains controversial, but this study reveals that it primarily responds to precessional insolation forcing and later exhibits heightened sensitivity to ice volume and CO2 related feedbacks. The variability of the summer monsoon is closely related to the thermal evolution of the Indo-Pacific Warm Pool and the strength of the Walker circulation. Meanwhile, the productivity proxy records consistently track glacial-interglacial variability, reflecting changes in polar ice fluctuations and Hadley circulation strength. The study concludes that the Australian Monsoon underwent a major re-organization and extratropical feedbacks were crucial in driving short- and long-term variability.