Evolution of the Australian Monsoon across the Middle Pleistocene Transition

The Australian Monsoon (AM) represents the Southern Hemisphere component of the large-scale Australasian monsoon system, which impacts the ecology, economy, and sustainability of some of the most densely populated regions on Earth. Located at the southern edge of the largest amplitude seasonal swing of the Intertropical Convergence Zone (ITCZ), the AM shows a different pattern of temporal variability compared to its Northern Hemisphere counterparts. However, most records of AM past variability are from the Holocene and Late Pleistocene, which limits our understanding of the AM long-term evolution. This thesis is based on sediment cores recovered at the International Ocean Discovery Program (IODP) Expedition 363 Site U1483, off northwestern Australia, which provide a unique record of the AM development over the past 2 million years (Ma). This study focuses on the evolution of the summer and winter phases of the AM across the Middle Pleistocene Transition (MPT). This highly enigmatic period was characterized by a remarkable change in climate cyclicity from 41 to 100 kyr. I performed oxygen and carbonate isotope analysis of benthic foraminifera and used X-ray fluorescence (XRF) core scanning records, spectral natural gamma-ray data, visible light reflectance spectroscopy data and benthic foraminifera assemblages to generate high-resolution proxies of AM variability over the last 1.6 Ma. Studies of radiolarian assemblages and bulk nitrogen isotopes in cooperation with researchers from institutions in Japan and the USA allowed additional insights into the variability of the Indonesian Throughflow and variations in paleoproductivity along the northwestern Australian margin over the last 2 Ma.