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Despite the crucial role of the Southern Hemisphere (SH) westerlies in modulating modern and past climate evolution, little is known about their behavior and possible forcing mechanisms during the early Cenozoic. We probe changes in the hydroclimate of southwest Australia during 62–51 Ma, based on sedimentary proxy records from the International Ocean Discovery Program Site U1514 in the Mentelle Basin. Our results reveal a transition from a less humid climate to wetter conditions at mid–high latitudes starting from the early Eocene, which suggests poleward migration of the SH westerlies. This long‐term trend is punctuated by short‐lived events of aridification during the Mid‐Paleocene Biotic Event and wetter intervals during the Paleocene‐Eocene Thermal Maximum, indicating additional short‐term meridional shifting of the westerlies. We propose that the evolution of SH westerlies was driven by the equator‐to‐pole temperature gradient regulated by global warming and ephemeral growth of the Antarctic ice sheet. Plain Language Summary: The Southern Hemisphere (SH) westerlies, which are the dominant atmospheric circulation patterns in the middle latitudes, play a key role in regulating global and regional climate. Currently, the knowledge of past changes in SH westerlies relies mainly on the late Quaternary. Its dynamics over longer timescales, especially under early Cenozoic greenhouse climate states, remain poorly understood. The Mentelle Basin off southwest Australia was located at a more southerly location than at the present day, and was potentially under the influence of SH westerlies. To examine the long‐term hydroclimate changes in southwest Australia during the mid‐late Paleocene to the early Eocene (62–51 Ma), we measured neodymium and hafnium isotopic compositions of fine‐grained detrital sediments from a borehole (IODP Site U1514) drilled in the Mentelle Basin, in addition to clay mineralogy, and elemental abundances. Our results suggest a gradual wetting of southwest Australia since the early Eocene, which we relate to the poleward migration of SH westerlies in response to a reduced latitudinal temperature gradient. An abrupt northward shift of SH westerlies was observed during the short‐lived Middle Paleocene Biotic Event (∼59 Ma), possibly driven by ephemeral growth of the Antarctica ice sheet. Key Points: We reconstruct the hydroclimate evolution of southwest Australia during 62–51 MaThe Southern Hemisphere (SH) westerlies remained relatively stable during the mid‐late Paleocene and shifted poleward since the early EoceneProcesses related to variations of pole‐equator temperature gradients drove meridional migration of the SH westerlies [ABSTRACT FROM AUTHOR]

At present, the seasonal melting and expansion of the Antarctic ice sheet affect the location and intensification of the westerlies, as well as the precipitation and continental weathering and erosion in southwest Australia. The Miocene was an important period when the Earth's climate state transitioned from a warmhouse to an icehouse and the East Antarctic Ice Sheet underwent large-scale melting and expansion. At that time, Australia was closer to the Antarctic region than it is now. This makes Australia an ideal target area for studying the coupling relationship among the atmosphere, hydrosphere, lithosphere, and cryosphere. Based on the comprehensive analysis of the siliciclastic mass accumulation rate, grain size, clay minerals, and elemental composition of the sediments at Site U1516 of the International Ocean Discovery Program Expedition 369, we reconstructed the Miocene climate evolution and the continental weathering and erosion history of southwest Australia on a tectonic time scale. Our indicators show that the climate was dry and that continental weathering and erosion were weak, with a small amount of terrestrial material transported to the ocean during the Early to Middle Miocene (22–12.7 Ma). However, as mentioned in previous studies of nearby sites, precipitation and river runoff increased prominently with enhanced continental weathering at 12.7–8 Ma, which was related to the northward migration or intensification of the westerlies, possibly due to increased sea ice in the Southern Ocean. In addition, we found that the evolution of the South Asian monsoon and the westerly belt were synchronized in the Miocene, which indicates that the South Asian monsoon system at that time may also have been affected by the high-latitude signals of the Southern Hemisphere. We speculate that the significant decrease in deep-sea temperature and the expansion of the surface sea temperature gradient in latitude and longitude until the permanent East Antarctic Ice Sheet formed (∼12.8 Ma) played an important role in the transmission of Antarctic signals to low latitudes. [ABSTRACT FROM AUTHOR]

Oceanic anoxic event 1d (OAE 1d) has been well studied at northern low latitudes (i.e., in Tethys and the North Atlantic); however, the paleoenvironmental response to this event at high latitudes has not been documented and the triggering mechanism remains unknown. Here, we address both of these shortcomings by presenting the first detailed sedimentary and multi‐proxy geochemical record of the OAE 1d at southern high latitudes (60–62°S), obtained from sediments using Site U1513, IODP Expedition 369. Biostratigraphic and chemostratigraphic data support correlation of the interval studied with OAE 1d, and the sedimentary mercury proxy reveals that at least at Site U1513, OAE 1d is associated with the Central Kerguelen large igneous province volcanism. Furthermore, the significant increase in continental runoff and consequent terrigenous input from southwestern Australia in the southeastern proto‐India Ocean might have resulted in regionally weakened bottom‐water oxygenation and strengthened organic matter burial during OAE 1d. Plain Language Summary: Geological marine records hold valuable information that could inform predictions for the future of our warming world. Marine sediments are an important reservoir of the global organic carbon and changes at the seafloor can modulate release of CO2 into the atmosphere. Cretaceous oceanic anoxic event 1d (∼latest Albian) was a significant disturbance to the global carbon cycle in the mid‐Cretaceous although it is poorly documented in the southern hemisphere especially at high latitudes. Our integrative sedimentary‐geochemical study demonstrates that oceanic anoxic event 1d at southern high latitudes might have been directly triggered by Central Kerguelen large igneous province volcanism. Volcanic emissions are proposed to have shifted the climate such that runoff and input of terrigenous sediment from southwestern Australia increased. These changes would have weakened bottom‐water oxygenation and increased organic matter burial in the southeastern proto‐Indian Ocean. Key Points: We present the first sedimentary and geochemical records for oceanic anoxic event 1d at southern high latitudes (60–62°S)Environmental changes during oceanic anoxic event 1d might be directly triggered by Central Kerguelen large igneous province volcanismMultiple paleoenvironmental changes occurred in the study area during oceanic anoxic event 1d [ABSTRACT FROM AUTHOR]

• A comprehensive Hg and Os isotopic record was reconstructed for the entire Eocene. • Isotopic signals indicate enhanced volcanism and continental weathering in the mid-Eocene. • A prolonged warmth lasting for ∼5 Myr is identified in the mid-Eocene. • A clear link between continental weathering and climate is evident during the MECO. • The Eocene climate is closely linked to active plate tectonic-driven volcanic activity. Rapid plate reorganization may have influenced global climate during the Eocene; however, its linkage remains poorly constrained, particularly during the middle Eocene. To elucidate this tectonic–climatic relationship, here, we conducted a comprehensive analysis based on high-resolution mercury (Hg) and osmium (Os) abundance and isotope data obtained from the complete Eocene sedimentary sequence of Site U1514, drilled in the Mentelle Basin off southwest Australia. The Hg signals in this sedimentary sequence, which are characterized by significantly high enrichment and insignificant mass-independent fractionation (Δ199Hg) signal, confirm that the middle Eocene (∼45–38 Ma) was a period of persistent, increased volcanism, accompanied by intense tectonic activity. In particular, a remarkable seafloor volcanic eruption persisted for approximately 1.5 million years (∼42.0–40.5 Ma), immediately preceding the Middle Eocene Climate Optimum (MECO). Contemporaneously, the trends toward a slightly more radiogenic seawater 187Os/188Os (Os i) composition denote the prevalence of intensified continental weathering under a warm, humid climate during the middle Eocene, a phenomenon particularly evident during the MECO. Importantly, the Hg and Os records from Site U1514 reveal the occurrence of a multi-million-year warming reversal amid the long-term Eocene cooling trend, which likely contributed to significant CO 2 reduction during the late Eocene. These findings significantly enhance our understanding of Eocene climate dynamics, which are fundamentally linked to intensive tectonic-driven volcanic activity and associated continental chemical weathering. [ABSTRACT FROM AUTHOR]

The Oceanic Anoxic Event 2 (OAE 2) represents one of the most profound global environmental disturbances of the Mesozoic Era, which was associated with a positive carbon isotope excursion due to widespread organic carbon burial. However, the character, evolutionary history, and exact driving mechanisms of OAE 2 are still much debated, exacerbated by the lack of records from climate-sensitive southern high latitudes. Here we present a multi-proxy record of a stratigraphically continuous succession spanning the late Cenomanian to early Turonian at the International Ocean Discovery Program Site U1516 in the Mentelle Basin off southwest Australia, which was located at southern high latitudes (~ 60–62°S) during the Late Cretaceous. Sedimentary records at Site U1516 allow the first detailed insights into source-to-sink processes in the Mentelle Basin and associated paleoenvironmental reconstruction in the southern Indian Ocean during OAE 2. Rare earth element abundances and clay-bound neodymium isotopes of the siliciclastic sediment fractions indicate that southwest Australia was the main detrital source of sediment at Site U1516 during OAE 2, with volcanogenic sediments representing only a minor component. A major provenance shift is observed across OAE 2, indicating an increased sediment contribution from distant sources (i.e., Yilgarn Craton and Albany-Fraser Orogen) relative to proximal sources (i.e., Perth Basin and Leeuwin Block) in southwest Australia, interpreted as reflecting a major reorganization of the drainage system due to enhanced fluvial runoff. Based on these findings, we infer that the OAE 2 interval showing the most prominent δ13C excursion was associated with an intensification of the hydrological cycle in the high-latitude southern hemisphere, with potential impacts on regional ocean chemistry and marine productivity. In particular, we suggest that enhanced terrigenous input and riverine nutrient export likely played a key role in controlling siliceous productivity at nearby ocean margins. As a consequence, the intense burial of organic matter (i.e., black shale) at Site U1516, which occurred episodically throughout OAE 2, possibly resulted from the combination of enhanced riverine-driven marine productivity and increased burial efficiency associated with the development of anoxic/euxinic bottom water conditions. • First detailed investigation of the source-to-sink process of the Mentelle Basin during OAE 2. • Geochemical records indicate dominant detrital contribution from Southwest Australia during OAE 2. • Enhanced hydrological cycle at southern high latitudes occurred during the interval with the most prominent δ13C excursion. • Multi-proxy records suggest a tight link between oceanic and continental changes during OAE 2. [ABSTRACT FROM AUTHOR]

The Oceanic Anoxic Event 2 (OAE 2; ca. ∼94 Ma) represents one of the most extreme carbon cycle perturbations of the Phanerozoic, which coincided with major environmental and climate reorganization in both terrestrial and marine realms. Chemical weathering of continental silicate rocks is thought to have played a crucial role during OAE 2, through enhanced release of bio-essential nutrients to the ocean, promoting high rates of marine primary production and organic carbon burial, but also due to its effect on atmospheric CO 2 drawdown, which altogether possibly drove the OAE 2 termination. Yet, the evolution of continental chemical weathering during OAE 2 remains poorly defined, especially in high-latitude regions. In this study, we present a combined hafnium-neodymium isotope investigation of the clay-size detrital fraction (△ ε Hfclay) of late Cenomanian to early Turonian sediments from the southwest Australian margin, at a site (International Ocean Discovery Program U1516) located in the southern high latitudes (∼62°S) during the late Cretaceous. The reliability of △ ε Hfclay as a proxy for continental chemical weathering in ancient anoxic marine sediments was assessed by analyzing a suite of samples retrieved from methanogenic sediments experiencing marine silicate weathering at ocean margins, suggesting negligible effect of reverse weathering on hafnium-neodymium isotope compositions. At Site U1516, the early stage of OAE 2 was characterized by relatively low △ ε Hfclay values (−5.9 ± 2), typical of reduced chemical weathering in nearby continental regions. At the onset of the most prominent carbon isotope excursion, an abrupt decrease in △ ε Hfclay points towards accelerated export of poorly weathered sediments resulting from the abrupt reactivation of river systems in southwest Australia. This period was followed by a pronounced △ ε Hfclay shift towards positive values, indicative of intensifying chemical weathering conditions during the OAE 2 interval showing the highest δ 13 C anomaly. Based on these results, we posit that enhanced hydrological cycle, most likely caused by a southward shift of the westerlies, led to a large increase in weatherability at southern high latitudes during peak OAE 2 warmth. This finding provides empirical support for the potential role played by high-latitude weathering systems in driving the termination of OAE 2, via weathering-driven consumption of atmospheric CO 2 and accelerated riverine fluxes of nutrients leading to enhanced organic carbon burial in marine sediments. • Combined Nd-Hf isotopes as a proxy for continental weathering during OAE 2. • Negligible influence of reverse weathering on Hf-Nd isotopes in marine clays. • Intensifying weathering and river discharge in SW Australia during peak OAE 2 warmth. • Southward shift of westerlies drove enhanced weatherability in southern high-latitude regions. [ABSTRACT FROM AUTHOR]

The Eocene was a critical period of global plate reorganization and it also saw the Earth's climate transition from the warmhouse state to the coolhouse state. Reconstructing the Eocene sedimentary history in the climate-sensitive Southern Ocean is important for understanding paleoenvironmental changes in response to the accelerated Australia/Antarctica separation and global cooling throughout the middle and late Eocene. Here, we present the first detailed multiproxy record of a continuous sequence from International Ocean Discovery Program (IODP) Site U1514 in the Mentelle Basin off southwestern Australia. Our aim is to reconstruct the sediment provenances and paleoenvironmental evolution in response to the abovementioned climatic and tectonic changes in the mid-high southern latitudes during the Eocene. Provenance analyses based on Sr-Nd isotopes, trace elements, and clay mineral assemblages suggest that Eocene sediments at Site U1514 predominantly originated from the southwestern Australian continent and the Naturaliste Plateau. Sediment provenance variations during the middle Eocene indicate that the onset of fast separation between Australia and Antarctica at 43 Ma caused an increased supply of volcanic materials from the Naturaliste Plateau between 43 and 38 Ma. Terrigenous inputs to the Mentelle Basin during the middle Eocene were primarily controlled by paleoclimate changes rather than tectonic processes because coeval clay mineralogical changes (higher kaolinite/smectite ratio and MAR kaolinite) indicate a period of stronger physical erosion and chemical weathering on the western Australian continent that resulted in increased terrigenous materials delivered to the Mentelle Basin. Our results reveal a 5 Myr-long (43–38 Ma) warming reversal in the southern mid-high latitudes, providing an exception to the generally short-lived (10–100 kyr-long) hyperthermals that interrupted the long-term global cooling throughout the middle to late Eocene. As for the late Eocene (38–37 Ma), tectonic processes related to the sudden acceleration in seafloor spreading in the Tasman Sea led to the exposure of shallower areas, resulting in rapid detritus accumulation at the study site. During the late Eocene (37–34 Ma), major sediment provenance shifted from distal source areas (e.g., the Yilgarn Craton) to relatively proximal sources (e.g., the Leeuwin Block and Perth Basin). We interpret that the regional uplift in southwestern Australia and coeval climate cooling resulted in the diversion and inactivation of large drainage systems, thus blocking the transportation of sediment from distant regions. • First detailed record of the Eocene source-to-sink process in the Mentelle Basin. • The onset of fast Australia/Antarctica separation caused increased volcanic input. • Regional warming led to enhanced chemical weathering in Australia during 43–38 Ma. • Regional uplift and global cooling induced sediment source change during 37–34 Ma. [ABSTRACT FROM AUTHOR]