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Abstract

Between ~1.2 Ma and 0.6 Ma, Earth’s glaciation gradually shifted from the 41-kyr to 100-kyr cycles, named as the mid-Pleistocene transition (MPT). Yet, it is unclear that how the Indonesian Throughflow (ITF), the only low-latitude shallow conduit of the global thermohaline circulation, behaved through this climate transition. Deep-sea sediments from the eastern Indian Ocean provide informative archives of the ITF over different timescales. In this study, we present high-resolution (~2 kyr) records of clay minerals from IODP Site U1483 drilled off northwest Australia to investigate variability of the ITF and terrestrial inputs associated with Australian monsoon since ~1.6 Ma. The results show that smectite (averaging 52%) dominates the clay assemblages, while kaolinite, illite, and chlorite contribute in moderate to scarce, with percentages of 23%, 18% and 7%, respectively. Kaolinite, illite and chlorite display a similar changing pattern and increases during interglacials, and the contrary situation occurs for smectite. Coupled study of clay minerals and Sr-Nd isotope reveals that smectite is mainly terrestrial clastic origin from inputs of the Fitzroy River and Ord River in the continent of northwestern Australia, while chlorite more likely originated from the Indonesian Archipelagos through transport of the ITF. Spectral and wavelet analyses reveal that frequency of clay minerals gradually shifted from the 41-kyr to 100-kyr periods between 1.3 Ma and 1.0 Ma. Our study provides a clue of sediments within the regime of the ITF surprisingly in response to sea level fluctuations and the tropical monsoon system.