The Indonesian Throughflow (ITF) serves as a major conduit of warm and relatively fresh Pacific waters into the Indian Ocean, playing a critical role in global climate regulation. Although tectonic constriction of the Indonesian gateway during the Pliocene (~4–3 Ma) is thought to have profoundly altered ocean circulation, the timing and mechanisms of ITF evolution remain poorly constrained due to lack of proximal, high-resolution records. Here, we present sea surface temperature and salinity records (~2.25 kyr resolution) spanning ~4.2–3.1 Ma from International Ocean Discovery Program Site U1482 in the Timor Sea, the main outflow pathway of the ITF. Our results reveal that warm and saline conditions were consistently phase-locked to precession minima and obliquity maxima, reflecting enhanced ITF transport driven by strengthened inter-basin pressure gradients and amplified interhemispheric insolation gradients. A significant shift in ITF surface hydrology occurred at ~3.6 Ma, marked by ~2°C surface cooling and ~0.4 ‰ freshening, and a transition from precession- to obliquity-dominated variability. Synthesizing regional records, we attribute this shift to a synergistic convergence: progressive tectonic constriction blocked the warmer, saltier South Equatorial Current, while onset of the Northern Hemisphere glaciation invigorated the Northern Hemisphere Hadley circulation. It suggests that Pliocene ITF surface hydrology was not solely governed by either orbital or tectonic forcing, but by their complex and evolving synergy. Our study highlights the Indonesian gateway as a critical node in the global ocean-climate system, influence of which is shaped by interplay of tectonic boundary conditions, high-latitude teleconnections and tropical orbital forcing.

The Indo-Pacific Warm Pool (IPWP) exerts a major influence on global atmospheric circulation, yet the drivers of late Pleistocene IPWP sea surface temperature (SST) variability remain debated. To evaluate how IPWP temperature responds to different climate forcings, we present new SST records spanning the past 650 kyr based on three independent proxies-, , and Mg/Ca-from International Ocean Discovery Program Site U1482, located off northwestern Australia at the southernmost margin of the IPWP. Core top samples suggest that and Mg/Ca are biased toward austral summer, while is elevated under low-nutrient conditions. Down-core, all proxies exhibit coherent glacial-interglacial SST variations of similar to 5C, although is affected by nutrient stress during interglacials. The record shows relatively warm conditions during Marine Isotope Stage 6 compared to other glacial intervals, but this is not observed in the or Mg/Ca records. Total alkenone concentration, reflecting paleo-productivity, indicate enhanced productivity during glacial intervals and reduced productivity during interglacials. The SST proxy records are in phase with greenhouse gas and ice volume in the 100 and 41 kyr orbital bands, emphasizing tropical-high latitude climate coupling, while local precession forcing impacts seasonal SSTs. Productivity variations track both glacial-interglacial cycles and precession-driven changes in wind-driven upwelling and surface current intensity in the Indo-Pacific. Our regional synthesis highlights sea-level and shelf exposure as key drivers of IPWP SST patterns, with a more pronounced precession influence at the southern IPWP margin. Our findings demonstrate that both glacial-interglacial cycles and precession govern SST and productivity variations in the IPWP.

Upper ocean temperature and stratification play essential roles in regulating hydrological processes from regional to basin scales and in shaping climate systems. The Eastern Tropical Indian Ocean (ETIO), as a major source of heat and moisture, is critical to regional and large-scale hydroclimatic variability. However, the longterm evolution of its upper water thermal structure remains poorly constrained. Here, we reconstruct sea surface temperature (SST) and thermocline water temperature (TWT) records spanning the past 620 ka using planktonic foraminiferal Mg/Ca ratios from Core 18548 and IODP Site U1482 off the northwest Australian margin. The results reveal that both SST and TWT exhibit pronounced glacial-interglacial cyclicity, primarily paced by orbital-scale forcing, including the 100-ka and precession (23/19-ka) periodicities. Notably, TWT displays a stronger precession signal than SST. These orbital-scale variations reflect the modulation of heat transfer to the ETIO through sea-level-controlled Indonesian Throughflow (ITF) dynamics and precession-driven atmospheric circulation. The amplified TWT response arises from the combined effects of ITF-mediated thermocline advection and insolation-induced vertical mixing, which together regulate upper ocean heat redistribution. A significant shift in the gradient between SST and TWT (Delta T) around 400 ka, coinciding with the MBE, indicates a major reorganization of upper ocean thermal structure, likely driven by glacioeustatic sea-level fluctuations and changes in precession-induced wind systems. Our findings highlight the coupled forcing of 100-ka cycle and precession on upper ocean thermal evolution in the ETIO and offer critical insights into orbital-scale heat redistribution and tropical ocean-climate interactions.

The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2) severely disrupted the global carbon cycle with widespread deposition of organic-rich marine sediments, resulting in a positive carbon isotope excursion. The Eastbourne section in southeastern England offers extensive benthic and planktonic foraminiferal data, revealing four distinct paleoenvironmental intervals across OAE 2. The Grey Chalk interval below OAE 2, which is characterized by the highest species diversity of benthic foraminifera, represents outer neritic-upper bathyal paleodepths, oxygenated environments and low organic fluxes at the seafloor. Deep- and thermocline-dwelling planktonic foraminifera suggest meso-oligotrophic regimes with a well-stratified water column. The onset of OAE 2 in Bed 1a of the Plenus Marl is marked by a sea-level fall supported by the maximum peak in abundance of shallow water agglutinated foraminifera (Ataxophragmium depressum, Arenobulimina, Plectina cenomana) and by the disappearance of bathyal taxa (e.g., Tristix excavata, Kalamopsis grzybowsky). In Bed 1b of the Plenus Marl, corresponding to the onset of the Plenus Cold Event, Eggerellina, Gaudryina, and Textularia replace shallow agglutinated taxa indicating a transgressive phase. This assemblage also coincides with the occurrence of Boreal planktonic foraminifera that suggests the incursion of Boreal waters into the Anglo-Paris Basin. The White Chalk, in the upper part and the interval above OAE 2, is interpreted as a Transgressive and Highstand Systems Tract with a change in the benthic foraminiferal assemblage towards the dominance of Marssonella, Gavelinella, Lingulogavelinella and Tritaxia with warmer and more mesotrophic waters recorded by the dominance of Tethyan planktonic foraminifera. (c) 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The Oceanic Anoxic Event 2 (OAE 2), across the Cenomanian-Turonian boundary interval, was characterized by global environmental perturbations in the carbon cycle that affected the abundance and biodiversity of marine biota and their paleoecological preferences. International Ocean Discovery Program (IODP) Sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia) reveal a continuous foraminiferal record that document the adaptative response of biota, suitable to reconstruct paleoenvironmental conditions in the water column and at the seafloor. Below and during the initial part of the OAE 2, we do not observe changes in the benthic foraminiferal assemblages dominated by Gavelinella, Gyroidinoides and Stensioeina. Agglutinated foraminifera are rare, whereas Microhedbergella and Muricohedbergella dominate the planktonic foraminiferal assemblage, indicating possible eutrophication episodes below and during the OAE 2 associated to an increase in terrigenous sediments. However, a positive peak in Zr/Rb ratios, the unique occurrence of Stensioeina truncata, and the increase in epifaunal- infaunal ratio, particularly at Site U1516, indicate a greater eolian transportation of sediments and an enhanced oxygenation at the seafloor, which might be related to the identification of the Plenus Cold Event (PCE) at high latitudes. An interval of low CaCO3 content within the peak of OAE 2 is characterized by the absence of foraminifera and dominance of siliceous organisms. It is also marked by a sudden enhancement of the hydrological cycle, probably causing a shoaling of the Calcite Compensation Depth (CCD). However, Site U1516 shows few samples with a change in the planktonic and benthic foraminiferal assemblage. Above this interval, both sites are characterized by a different benthic foraminiferal assemblage with the occurrence of Conorboides claytonensis in the uppermost part of OAE 2. At Site U1513, epi-infaunal ratio increase, planktonic foraminifera show the highest diversification, rainfall decreases, indicating a recovery towards a wellstratified water column with mesotrophic regimes and a drier environment, whereas Site U1516 shows a slower recovery.

Surface hydrology in the tropical eastern Indian Ocean significantly impacts low-latitude climate processes including the Indonesian-Australian Monsoon and the Indian Ocean Dipole. Deciphering the evolution of surface hydrology and driving mechanisms is thus important to better understand low-latitude and global climate change. Here, we present ~206 yr-resolved temperature and salinity records of surface waters spanning the past ~31 kyr, based on δ18O and Mg/Ca ratio of Globigerinoides ruber from Core SO18567 retrieved offshore northwestern Australia in the tropical eastern Indian Ocean. By integrating new records with published paleo-oceanographic and -climatological records, we found that increasing sea surface temperature and decreasing salinity in the tropical eastern Indian Ocean during the Heinrich stadial 1 and the Younger Dryas could be attributed to collapse of the Atlantic Meridional Overturning Circulation (AMOC). Melting of Northern Hemisphere ice sheets would have led to a southward shift of the Intertropical Convergence Zone (ITCZ) and reduced transport of warm surface waters from the low latitudes to the Northern Hemisphere high latitudes. In addition, our results indicate that the onset of the last deglacial warming in low latitudes was linked to weakening of the Hadley circulation and AMOC due to warming of Northern Hemisphere high latitudes, rather than raised global atmospheric CO2 concentration.

AbstractThe 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.

Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700-800 m of the section captured in detail not available with industry seismic data. We present nine new high-resolution seismic lines from three separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300 m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.

The Cretaceous marine sediments of Morocco and adjacent coastal basins provide an outstanding archive of environmental diversity from extended shelf seas and marginal basins along the Atlantic and Tethyan margins to deep oceanic basins of the western Tethys and eastern Atlantic Ocean. The geological highlights of Morocco's fascinating landscape include records of Lower Cretaceous Tethyan marginal and deep-water clastic sequences in the Rif mountain chain (submarine fan systems of the Massylian and Mauretanian flysch units), as well as siliciclastic sedimentary sequences in subsiding coastal basins (TanTan Delta), which extend offshore along the NW African Atlantic margin. Vestiges of the Aptian to Turonian greenhouse climate, sea-level highstands and oceanic anoxic events are exceptionally well preserved in Tethyan marginal and deep-water sedimentary successions of the Rif, in Atlantic coastal basins and as transgressive pulses on the Moroccan Meseta, Sahara platform and High Atlas rift system. Furthermore, sedimentary expressions of the tectonic movements between the African and European plates associated with the end Cretaceous climate and sea-level changes are documented in the Rif mountain chain, in coastal basins, and in the massive marginal marine phosphorite sedimentation in the Middle and High Atlas, on the Moroccan Meseta and Sahara platform. The Cretaceous sedimentary archives from Morocco and adjacent coastal basins still retain untapped potential to further contribute to our understanding of global eustatic sea-level changes and the response of the oceans and marine biota in upwelling driven oxygen minimum zones under greenhouse climate conditions.

AbstractThe response of the ocean overturning circulation to global warming remains controversial. Here, we integrate a multiproxy record from International Ocean Discovery Program Site U1490 in the western equatorial Pacific with published data from the Pacific, Southern and Indian Oceans to investigate the evolution of deep water circulation during the Miocene Climate Optimum (MCO) and Middle Miocene Climate Transition (MMCT). We find that the northward export of southern-sourced deep waters was closely tied to high-latitude climate and Antarctic ice cover variations. Global warming during the MCO drove a progressive decrease in carbonate ion concentration and density stratification, shifting the overturning from intermediate to deeper waters. In the western equatorial Pacific, carbonate dissolution was compensated by increased pelagic productivity, resulting in overall elevated carbonate accumulation rates after ~16 Ma. Stepwise global cooling and Antarctic glacial expansion during the MMCT promoted a gradual improvement in carbonate preservation and the initiation of a near-modern Pacific overturning circulation. We infer that changes in the latitudinal thermal gradient and in Southern Ocean zonal wind stress and upper ocean stratification drove radically different modes of deep water formation and overturning across the MCO and MMCT.

The Global Stratotype Section and Point (GSSP) of the base of Langhian Stage (base of the Middle Miocene Sub- series) is defined at a level of 17.84 m in the "Lower La Vedova Beach" section in central Italy. This level marks the mid-point of the darker marly interval above "Megabed IV" which has been astronomically calibrated to the most prominent similar to 100-kyr eccentricity maximum, with an astronomical age of 15.981 Ma according to La2004 nominal solution, and of 15.978 Ma according to the La2011, in the 405-kyr maximum around 16.0 Ma. The GSSP level in the Lower La Vedova Beach section corresponds closely to the top of Chron C5Cn (at 15.795 m), which is considered the principal event for recognizing the boundary globally. This magnetic reversal with an astronomical age of 16.017 Ma (Turco et al., 2017) (15.97 Ma in Hilgen et al., 2012 ATNTS, 2012; 15.994 Ma in Raffi et al., 2020 in GTS2020) is preferred to the historical guiding criterion, the Praeorbulina datum, which has been complicated by taxonomic confusion and revision (Turco et al., 2011a), and hence is considered less suitable for recognizing the boundary. The Lower La Vedova Beach section is preferred to the St. Peter's ' s Pool section (in Malta) as it has an independent astronomical tuning and a better paleomagnetic signal. With the selected astrochronologic criterion close to an important magnetic reversal boundary we follow standard procedures developed by SNS to define Neogene GSSPs over the years. This procedure guarantees that the Langhian GSSP is directly incorporated in the integrated astronomically dated stratigraphic framework that nowadays underlies our standard GTS, while it is sufficiently close to the top of Chron C5Cn that the latter can be used for correlating the boundary time-strati- graphically on a global scale. In addition, a Standard Auxiliary Boundary Stratotype (SABS) is designated at Integrated Ocean Drilling Program (IODP) Site U1337, in the eastern equatorial Pacific, with the aim to directly link the open ocean benthic foraminiferal stable isotope record to the boundary definition. This level marks the mid-point of a darker interval that has been astronomically calibrated to the same prominent similar to 100-kyr eccentricity maximum. This level coincides with distinctive features in the stable isotope record, falls right in the middle of the Miocene Climatic Optimum (MCO) and is approximately one 405-kyr cycle older than the most dramatic oxygen isotope minimum dated astronomically at 15.6 Ma, marking the most extreme warming during the entire Miocene (Holbourn et al., 2013). It further corresponds closely to the top of Chron C5Cn, based on detailed cyclostratigraphic correlations to parallel Sites U1335 and U1336, which have an excellent magnetostratigraphy. Biostratigraphically, the Langhian GSSP falls in the lower part of the Mediterranean planktonic foraminiferal Sub- zone MMi4a (Di Stefano et al., 2008; Iaccarino et al., 2011; Lirer et al., 2019), delimited by the First Occurrence (FO) of Globigerinoides sicanus (3 apertures) at the base and the Beginning of the Paragloborotalia siakensis Acmea a at the top, and calcareous nannofossil Subzone MNN4b (Di Stefano et al., 2008; 2023), defined by the Last Common Occurrence (LCO) of Helicosphaera ampliaperta and the Beginning of the Sphenolithus heteromorphus Paracme interval. With respect to (sub)tropical biozonations, the Langhian GSSP falls within the planktonic foraminiferal Zone M5 (Wade et al., 2011) and Zone N8 (Blow, 1969), defined by Base Praeorbulina sicana (B) and Base Orbulina suturalis, , and at the top of the calcareous nannofossil Zone CNM6 (Backman et al., 2012), defined by Base S. heteromorphus and Base Discoaster signus (= D. petalosus), corresponding to the upper part of Zone NN4 (Martini, 1971).

This Special Issue on Recent advances in Indian Ocean Paleoceanography and Paleoclimate comprises thirteen research articles. Contributions variously discuss Neogene oceanographic evolution of the tropical Indian Ocean in relation to global climate change, oxygenation, acidification and its effects on calcifying phytoplankton, variability of the Indian-Australian monsoon and monsoon-response to external forcing and internal feedbacks. Some key findings are as follows: Hyperthermal events at eccentricity maxima during the Miocene Climatic Optimum led to the acidification of poorly ventilated deep waters and carbonate dissolution in the equatorial Indian Ocean. During the Middle Miocene Climatic Transition, intensification of deep ocean ventilation at low-latitudes following Antarctic ice sheet expansion prevented re-establishment of hyperthermal conditions after similar to 13.1 Ma. Bottom water conditions in the eastern Arabian Sea remained oxic during the late Miocene-Pliocene, but shifted to suboxic during the Pleistocene, most likely due to the combined effect of decreasing deep-water ventilation and enhanced monsoon circulation. During this interval, changes in monsoonal winds and the inter-ocean transfer of water masses through the Indonesian Throughflow strongly affected the surface-subsurface dynamics of the tropical Indian Ocean. Shoaling of the thermocline in the tropical eastern Indian Ocean occurred between 6 and 3.4 Ma in response to intensification of the Indian summer monsoon. Enhanced Indonesian Throughflow resulted in intensification of cross-equatorial sea surface temperature and pressure gradients and increased summer monsoon precipitation at 2.95 Ma, as inferred from Arabian Sea proxy records. Eastward flowing nutrient-rich, saltier water influenced the surface hydrography of the tropical eastern Indian Ocean between 2.7 and 1.2 Ma. Variations in Indian monsoon precipitation and wind intensity acting in concert with Northern Hemisphere climatic oscillations drove millennial- to centennial-scale changes in surface hydrography and productivity in the Bay of Bengal and Andaman Sea during the late Glacial-Holocene. Rapid intensification of Australian summer monsoon precipitation at the end of glacial terminations coincided with maxima in atmospheric CO2 and CH4 concentrations and in Antarctic temperature. Evidence presented in this special issue indicates that greenhouse gas concentrations and high latitude climate in conjunction with variations in the insolation gradient between the Southern Hemisphere tropics and subtropics modulated the strength of the tropical convection, the latitudinal migration of the Inter-Tropical Convergence Zone and the intensity of the Indian-Australian monsoon.

A planktic foraminiferal mass extinction, coeval with the major carbon cycle perturbation of Oceanic Anoxic Event (OAE) 1b, occurred at the Aptian−Albian boundary interval (AABI). However, the scarcity of high-resolution records across the AABI hampers an assessment of the impacts of OAE 1b on deep-water benthic foraminiferal assemblages. Here we present high-resolution benthic foraminiferal census counts at Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic Ocean) and Ocean Drilling Program (ODP) Site 1049 (western subtropical North Atlantic Ocean) over the AABI. Our records at these bathyal sites provide conclusive evidence that there was no benthic foraminiferal extinction at the Aptian−Albian boundary, although marked reorganizations of relative abundances occurred. During the latest Aptian, cyclic increases in the abundance of infaunal species at both sites point to repeated pulses of reduced bottom water oxygenation and increased organic carbon flux to the ocean floor. Additionally, agglutinated and weakly calcified benthic foraminiferal species were relatively abundant during the latest Aptian, suggesting deep-water carbonate ion depletion in the Atlantic Ocean, although we did not identify signs of carbonate dissolution at these relatively shallow sites. At Site 511, abundances of infaunal foraminifera increased in tandem with the negative carbonate carbon isotope (δ13Ccarb) excursion of the Kilian sub-event within OAE 1b, suggesting decreased bottom water ventilation and increased organic carbon flux to the ocean floor during the sub-event. Bottom water ventilation and carbonate ion saturation improved during the earliest Albian in the Atlantic Ocean, followed by high-amplitude oscillations, as suggested by abundance trends of heavily calcified epifaunal foraminifera at Sites 511 and 1049.

The Cenomanian-Turonian boundary interval is characterized by environmental perturbations related to the Oceanic Anoxic Event 2 (OAE 2) that severely affected the marine biota, including benthic and planktonic foraminifera. We present a continuous high-resolution benthic foraminiferal record in combination with published planktonic foraminiferal and geochemical data across the Cenomanian-Turonian boundary interval in the Clot Chevalier section (Vocontian Basin, SE France) with the aim to interpret paleoceanographic changes in bottom waters. Benthic foraminiferal assemblages are characterized by low diversity and indicate an outer shelfupper bathyal environment. Changes in composition and abundance of the benthic assemblages throughout the stratigraphic section allow identification of seven distinct environments. In the middle Cenomanian, below the OAE 2, benthic foraminifera show high species diversity and abundance of infaunal and epifaunal taxa, suggesting an environment characterized by oxic conditions at the seafloor. The microfossil assemblages in the upper Cenomanian within the OAE 2 interval are dominated by radiolaria (> 50%) followed by benthic calcareous taxa (Gavelinella sp., Gyroidinoides sp., Praebulimina elata, Tappanina laciniosa). Benthic agglutinated taxa (Ammobaculites sp., Ammodiscus cretaceus, Gaudryina sp., Textulariopsis bettenstaedti) show high abundance in the lowest part of the OAE 2 and disappear close to the top of the interval. The assemblage composition and the highest values of Total Organic Carbon (TOC) registered in this interval suggest eutrophication and suboxic conditions at the seafloor. However, at similar to 1 m above the onset of the OAE 2, the repopulation by inferred oxic benthic foraminiferal taxa (i.e., Frondicularia sp. and Ramulina aculeata) suggests ventilation of bottom water masses, recording the Plenus Cold Event (PCE). In the lowermost Turonian, the assemblages exhibit high species diversity and abundance with the re-appearance of calcareous taxa, indicating oxic conditions, and of agglutinated taxa associated to moderate oxygen concentrations. Results show that the distribution of benthic foraminifera follows fluctuations in oxygenation and carbon export flux at the seafloor interpreted as the environmental changes associated to the onset of the OAE 2 and of the PCE across the Cenomanian-Turonian boundary interval.

Arc-continent collision in Southeast Asia during the Neogene may have driven global cooling through chemical weathering of freshly exposed ophiolites resulting in atmospheric CO 2 removal. Yet, little is known about the cause-and-effect relationships between erosion and the long-term evolution of tectonics and climate in this region. Here, we present an 8-million-year record of seawater chemistry and sediment provenance from the eastern Indian Ocean, near the outflow of Indonesian Throughflow waters. Using geochemical analyses of foraminiferal shells and grain size–specific detrital fractions, we show that erosion and chemical weathering of ophiolitic rocks markedly increased after 4 million years (Ma), coincident with widespread island emergence and gradual strengthening of Pacific zonal sea-surface temperature gradients. Together with supportive evidence for enhanced mafic weathering at that time from re-analysis of the seawater 87 Sr/ 86 Sr curve, this finding suggests that island uplift and hydroclimate change in the western Pacific contributed to maintaining high atmospheric CO 2 consumption throughout the late Neogene.

The Mid-Pleistocene Transition (MPT) between ~1200 and ~800 ka was associated with a major shift in global climate and was marked by a change in glacial/interglacial periodicity from ~41 to ~100 kyr that resulted in higher-amplitude sea-level variations and intensified glacial cooling. The Indonesian Throughflow (ITF), which controls the exchange of heat between the Pacific and Indian Oceans, is a major component of the global climate system. On the other hand, Asian-Australian Monsoon dynamics play a key role in regional primary productivity. Therefore, reconstruction of ITF and Asian-Australian Monsoon variability during the MPT could potentially clarify the impact of the glacio-eustatic sea level changes on the climate and ecosystem of Northwest Australia. The International Discovery Program (IODP) Expedition 363 retrieved an extended, continuous hemipelagic sediment succession spanning the past two million years at Site U1483 on the Scott Plateau off Northwestern Australia.In this study, we analyzed radiolarian assemblages in core top samples retrieved during the RV Sonne Expedition 257 and downcore samples from IODP Site U1483 to estimate the variability in regional sea surface temperatures (SSTs) during the MPT, and to explore ITF dynamics in relation to glacio-eustatic sea-level variations and tropical monsoon strength. We suggest that glacio-eustatic sea-level variations have been a key factor affecting changes in SSTs at Site U1483, primarily because the shallow and hydrogeographically complex nature of the sea means that SSTs are highly sensitive to glacio-eustatic sea-level variation. Based on comparisons with SST data from the mid latitudes off Northwest Australia and the South China Sea, we suggest that the SSTs at Site U1483 are highly dependent on prevailing climate changes in the northern hemisphere rather than changes in the climate of the Southern hemisphere. In addition, comparisons of radiolarian total abundances with X-ray fluorescence-scanning elemental data suggested that, until the onset of the MPT (~1200 ka), radiolarian productivity was higher during strong summer monsoons during interglacial periods, probably because of the high riverine runoff generated by heavy summer monsoonal precipitation. However, since ~900 ka, there appears to have been a shift in the mode of radiolarian productivity that has resulted in increased radiolarian productivity during glacial periods when the delivery of nutrients is increased due to the enhanced mixing of the upper water column in the shallow sea caused by strong trade winds.

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 ~0.95 Ma, but exhibited heightened sensitivity to ice volume and p CO 2 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 ~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.