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The Indonesian Throughflow (ITF) thermocline, as exclusive water source for the "warm water route" of the Atlantic Meridional Overturning Circulation (AMOC), provides waters that exit the Indian Ocean and join the AMOC upper limb via the Agulhas Leakage (AL). Hence, investigating long‐term variations in the ITF thermocline and its implications on the AL is important for understanding dynamics of the AMOC. Here, the thermohaline history of the ITF thermocline was reconstructed for the last ∼410 kyr based on δ18O and Mg/Ca of planktonic foraminifera from International Ocean Discovery Program Site U1483. By integrating the new and published records, we found that precession drives variation of the ITF thermocline through modulating the intensity of the Australian‐Indonesian winter monsoon, El Niño‐Southern Oscillation‐like states and formation of the North Pacific Tropical Water, in turn exerting a transoceanic influence on the amount of the AL and seawater temperature and salinity of the South Atlantic thermocline. Plain Language Summary: It is widely acknowledged that the Indonesian Throughflow (ITF), a key component of the global thermohaline circulation, plays an important role in the global climate and ocean circulation. However, in contrast to concentrating on the factors that shaped the ITF in the geological history, few studies considered the ITF as a factor to influence climate and ocean circulation, especially on long timescales. In this study, we utilized shell δ18O and Mg/Ca of a planktonic foraminiferal thermocline‐dwelling species from the Timor Sea, the main outflow passage of the ITF, to reconstruct the temperature and salinity changes of the ITF thermocline during the past ∼410 kyr. By integrating the new and published paleo‐oceanographic and ‐climatological records, we found that the ∼20‐kyr wobbles of the Earth's axis (precession) induced variations in the flow strength and seawater temperature and salinity of the ITF thermocline, and in turn regulated the amount of the Agulhas Leakage and seawater temperature and salinity of the South Atlantic thermocline. Our results underscore the essential role of the ITF in the connectivity among the oceans. Key Points: Precession drove variations in the ITF thermocline by modulating the intensity of the Australian‐Indonesian winter monsoon, ENSO‐like states and formation of the North Pacific Tropical WaterVariations in the ITF thermocline regulated the amount of AL and seawater temperature and salinity of South Atlantic thermocline [ABSTRACT FROM AUTHOR]

We collected a suite of core top samples during R/V Sonne Cruise SO257 in May 2017 along the southwestern front of the Indo‐Pacific Warm Pool (IPWP) to monitor the variability of Southern Hemisphere tropical and subtropical sea surface hydrology and to assess temperature and salinity reconstructions with data sets reflecting conditions in the post‐monsoonal season. In our core top samples, a steep increase in planktic δ18O, associated with a decrease in sea surface temperature (SST), indicates that the southwestern front of the IPWP is located between 23° and 24°S during austral fall. We additionally reconstructed SST, sea surface salinity ,and δ18O seawater (δ18Osw) over the last 450 kyr in two sediment successions located within and beyond the monsoonal rain belt. Our records show that SST was highly coherent and phase‐locked with atmospheric pCO2 during the last 450 kyr. The regional differences in the δ18Osw records reveal that the Western Australian Margin north of 15°S remained seasonally under the influence of IPWP water masses, even during glacials. The temporal variability in upper ocean hydrology along the Western Australian Margin is not directly coupled to local monsoonal precipitation, but is strongly affected by advective mixing of Indonesian Throughflow derived water masses. Key Points: Southwest front of modern Indo‐Pacific Warm Pool (IPWP) during austral fall is located between 23° and 24°SWestern Australian Margin north of 15°S remained seasonally influenced by IPWP throughout past 450 kyrUpper ocean hydrology off Western Australia represents an integrated signal of monsoonal precipitation and advective mixing [ABSTRACT FROM AUTHOR]

The Intertropical Convergence Zone (ITCZ), which is the heaviest rain belt on Earth, significantly influences global hydroclimate change and livelihood of nearly 40% of the global population. However, long‐term precipitation records are sparse from the Indo‐Pacific region, especially from the southern margin of the Indo‐Pacific ITCZ, restricting our understanding of the overall natural variability of the ITCZ in the past. In this study, we present a new summer monsoonal precipitation record that spans the last 410 kyr from the southern margin of the Indo‐Pacific ITCZ, based on the logarithmic ratio between terrigenous fraction K and pelagic fraction Ca (ln(K/Ca)). Contents of both elements were derived from X‐ray fluorescence scanning on sediment cores from Site U1483 (13°05.24′S, 121°48.25′E, water depth 1,733 m) that was drilled offshore northwestern Australia during International Ocean Discovery Program Expedition 363. Comparison of the new precipitation record with published precipitation records from the northern margin and meteorological center of the Indo‐Pacific ITCZ shows that precipitation changed nearly in‐phase between the hemispheres on the precession band, possibly linked to expansion and contraction in the latitudinal extent of the Indo‐Pacific ITCZ. In contrast, interhemispheric precipitation was nearly in anti‐phase on the obliquity band, likely due to latitudinal migration of the Indo‐Pacific ITCZ. Our findings imply that tropical hydroclimate cycles were regulated by the orbital forcing but with significantly different response to changes of the ITCZ on precession and obliquity bands. Key Points: A new summer monsoonal precipitation record that spans the last 410 kyr from the southern margin of the Indo‐Pacific ITCZ was presentedInterhemispheric precipitation in‐phasing on precession band could be linked to expansion and contraction of the Indo‐Pacific ITCZInterhemispheric precipitation anti‐phasing on obliquity band could be due to latitudinal migration of the Indo‐Pacific ITCZ [ABSTRACT FROM AUTHOR]