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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]

• 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]

We present a new set of clay mineral and grain-size data for the siliciclastic sediment fraction from International Ocean Discovery Program (IODP) Site U1456 located in the eastern Arabian Sea to reconstruct the variabilities in the continental erosion and weathering intensity in the western Himalaya, elucidate the sediment source-to-sink processes and discuss the potential controls underlying these changes since 3.7 Ma. The clay minerals mainly consist of smectite (0–90%, average 44%) and illite (3–90%, average 44%), with chlorite (1–26%, average 7%) and kaolinite (0–19%, average 5%) as minor components. The compositional variations in the clay minerals at IODP Site U1456 suggest four phases of sediment provenance: the Indus River (phase 1, 3.7–3.2 Ma), the Indus River and Deccan Traps (phase 2, 3.2–2.6 Ma), the Indus River (phase 3, 2.6–1.2 Ma) and the Indus River and Deccan Traps (phase 4, 1.2–0 Ma). These provenance changes since 3.7 Ma can be correlated with variations in the Indian summer monsoon intensity. The siliciclastic sediments in the eastern Arabian Sea were mainly derived from the Indus River when the Indian summer monsoon was generally weak. In contrast, when the Indian summer monsoon intensified, the siliciclastic sediment supply from the Deccan Traps increased. In particular, this study shows that the smectite/(illite+chlorite) ratio is a sensitive tool for reconstructing the history of the variation in the Indian summer monsoon intensity over the continents surrounding the Arabian Sea since 3.7 Ma. [ABSTRACT FROM AUTHOR]

We investigate the phased evolution and variation of the South Asian monsoon and resulting weathering intensity and physical erosion in the Himalaya–Karakoram Mountains since late Pliocene time (c. 3.4 Ma) using a comprehensive approach. Neodymium and strontium isotopic compositions and single-grain zircon U–Pb age spectra reveal the sources of the deposits in the east Arabian Sea, and show a combination of sources from the Himalaya and the Karakoram–Kohistan–Ladakh Mountains, with sediments from the Indian Peninsula such as the Deccan Traps or Craton. We interpret shifts in the sediment sources to have been forced by sea-level changes that correlate with South Asian monsoon rainfall variation since late Pliocene time. We collected 908 samples from the International Ocean Discovery Program Hole U1456A, which was drilled in the east Arabian Sea. Time series of hematite content and grain size of the sediments were examined downcore. We found South Asian monsoon precipitation and weathering intensity experienced three phases from late Pliocene time. Lower monsoon precipitation, with a lower variability and strong weathering intensity, occurred during 3.4–2.4 Ma; an increased and more variable South Asian monsoon rainfall, along with strengthened but fluctuating weathering intensity, occurred at 1.8–1.1 Ma; and a reduced rainfall with lower South Asian monsoon precipitation variability and moderate weathering intensity marked the period 1.1–0.1 Ma. Maximum entropy spectral analysis and wavelet transform show that there were orbital-dominated cycles of periods c. 100 and c. 41 ka in these proxy-based time series. We propose that the monsoon, sea level, global temperature and insolation together forced the weathering and erosion in SW Asia. [ABSTRACT FROM AUTHOR]

We present a multiproxy record of Sr‐Nd isotopes and major and trace elements for clay‐sized (<2 μm) siliciclastic sediment fractions from the International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to extract reliable chemical indicators not influenced by the grain‐size effect, quantitatively estimate detrital provenance, and constrain silicate weathering/erosion in response to the Indian summer monsoon over orbital timescales. A provenance analysis of fine‐grained siliciclastic sediments indicates a two end‐member mixture from the Indus River (20–90%) and rivers draining the Deccan Traps (10–80%). A prominent increase in terrigenous input from the Indus River occurred at ~0.5 Ma, probably resulting from an intensive erosional event in the Himalayan region. Moreover, αAlK at Site U1456, which is calculated as Al/K ratio of the study sample versus Al/K ratio of the upper continental crust, can be generally used to reflect the chemical weathering intensity in the source regions. During most interglacial and even certain glacial periods, the Indian summer monsoon reinforcement is closely coupled with enhanced continental chemical weathering and physical erosion. Wavelet and spectral analyses of the αAlK record display strong 125‐, 35‐, 29‐, and 23‐kyr periodicities since 1.2 Ma with significant ~100‐kyr cycles established at the end of the Mid‐Pleistocene Transition (~0.7 Ma), suggesting forcing mechanisms linked with both Northern and Southern Hemispheric processes. Significant fluctuations observed in silicate weathering/erosion during ~1.2–0.7 Ma indicate an enhancement of the Indian summer monsoon with increased variability in association with the Mid‐Pleistocene Transition. Key Points: Indus River and Deccan Traps supplied fine‐grained sediments to the eastern Arabian Sea since 1.2 MaThe Indian summer monsoon reinforcement can trigger strong chemical weathering and rapid continental erosion over orbital timescalesαAlK records indicate significant changes in the Indian summer monsoon in association with the Mid‐Pleistocene Transition [ABSTRACT FROM AUTHOR]

• First millennial-scale study on erosion and weathering of the western Philippine Sea. • Sea-level lowstand favored erosion and weathering of exposed shelf sediments. • Anthropogenic activity has been a dominant control on Luzon erosion since 2.1 ka. Multiproxy records from Core MD06-3054 in the western Philippine Sea and published results from the nearby Core MD06-3052, which are both located at the northern margin of the Western Pacific Warm Pool (WPWP), provide precise reconstructions and evidence for the potential controls on continental erosion and weathering intensities in Luzon. These data also constrain sediment source-to-sink processes in the sea since 27 ka at the millennial scale. We demonstrate that the siliciclastic fraction is derived from Luzon volcanic rocks and eolian dust from mainland Asia. Stronger physical erosion and chemical weathering generally occurred during the last glaciation, Heinrich Event 1, the Younger Dryas, and the period from 10.3 to 11.3 ka. In contrast, the Bølling-Allerød was characterized by weaker physical erosion and chemical weathering. During the last glaciation, Heinrich Event 1, and the Younger Dryas, the lower sea level led to enhanced erosion and weathering of the exposed shelf sediments. In contrast, the weaker physical erosion and chemical weathering that occurred during the Bølling-Allerød and the Holocene, except after 2.1 ka, are closely correlated with the higher sea level. The stronger physical erosion and chemical weathering at 10.3–11.3 ka may be derived from the reworking of older sediments during the time of a strengthening summer monsoon. Furthermore, enhanced human activity since 2.1 ka has become the dominant control on erosion in Luzon. Rapid weathering changes in the WPWP during the last deglaciation highlight the high variability in local controls at low latitudes during these periods and the potential influence of controls at high latitudes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The evolution of the Indian summer monsoon was reconstructed from IODP Site U1456. • The clay-sized detrital sediments are derived from Indus River and Deccan Traps. • A major transition recorded by clay mineralogy at ~0.9 Ma corresponds to the MPT. Abstract Clay mineral assemblages at International Ocean Discovery Program Expedition 355 Site U1456 drilled in the eastern Arabian Sea have been investigated to reveal the sediment provenances and reconstruct the erosion/weathering patterns in the western Himalaya and Indian subcontinent, thus constraining the evolution of the Indian summer monsoon and its forcing mechanism since 1.2 Ma. The clay mineral assemblages at Site U1456 mainly comprise smectite (with an average value of 59%) and illite (with an average value of 33%), with chlorite (with an average value of 5%) and kaolinite (with an average value of 3%) as minor constituents. In terms of sediment provenance, our results indicate that illite and chlorite are predominantly derived from the Indus River, which originates from the western Himalaya and Karakoram, while smectite is primarily sourced from the Narmada River and Tapti River in the Deccan Traps, with a non-negligible contribution from the Indus River in some cases. Variations in smectite/(illite + chlorite) ratio are ultimately controlled by the Indian summer monsoon, which is characterized by approximate glacial/interglacial cyclicity, showing higher values (i.e., enhanced chemical weathering) during interglacial periods. In addition, a major shift in smectite/(illite + chlorite) ratio at 0.9 Ma is correlated to the Mid-Pleistocene Transition (∼1.2–0.9 Ma). Both the Marine Isotope Stage 13 event (533–478 ka) and the Mid-Brunhes Event (∼430 ka) are also recorded in the clay mineral proxies. Based on the spectral analysis, smectite/(illite + chlorite) ratio displays a transition from nonprimary periodicity (29-kyr) to strong eccentricity (100-kyr) and precession (22-kyr) periodicities at approximately 0.9 Ma, which corresponds to the Mid-Pleistocene Transition. Our study indicates that the variability of the Indian summer monsoon at orbital timescales is controlled by high-latitude (i.e., ice volume) and low-latitude (i.e., summer insolation) processes. [ABSTRACT FROM AUTHOR]

We present a new high-resolution multiproxy data set of mass accumulation rates, Sr-Nd isotopes, as well as major and trace elements for the siliciclastic sediment fraction from International Marine Global Change Study Core MD06-3052, located on the continental slope of the western Philippine Sea. We integrate our new data with published grain sizes and sea surface temperatures from the same core, as well as with Equatorial Pacific sea level, and East Asian summer monsoon precipitation, in order to constrain at high-resolution changes in physical erosion and chemical weathering intensities on Luzon, and sediment source-to-sink processes. We assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric CO 2 since 156 kyr BP. Sr-Nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on Luzon (~ 68–100%), with a lesser contribution from Asian dust (~ 0–32%). Different indices indicate that stronger physical erosion and chemical weathering occurred during Marine Isotope Stage (MIS) 6 (130–156 kyr BP), as well as in the latter stage of MIS 3 and MIS 2 (14–40 kyr BP). The large sea-level lowstands and associated significant exposure of continental shelf in the western Philippine Sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf. Furthermore, we notice the relatively good coherence between chemical weathering intensities on Luzon and global atmospheric CO 2 concentrations over these cold intervals. We suggest that strengthening of chemical weathering of silicates on Luzon and other tropical arcs (within 20° of the Equator) during the Quaternary glacial sea-level lowstands may significantly contribute to the lowering of atmospheric CO 2 concentrations during ice ages. We estimate that a significant fraction, up to ~ 16% (i.e., ~ 8 ppmv), of all atmospheric CO 2 ultimately sequestered by silicate weathering may be processed through an area corresponding to only ~ 1% of the exorheic drainage area worldwide. [ABSTRACT FROM AUTHOR]

Changes in terrigenous organic matter (OM) input, productivity and the associated bottom-water redox conditions, together with forcing mechanisms and global carbon cycle implications of such variations, on the western margin of the Western Pacific Warm Pool (WPWP) during the Quaternary remain controversial. In this study, we reconstructed the hydrological dynamics, terrigenous OM input, productivity, and deep-sea redox conditions using one core from the continental slope of the Philippine Sea. The new data were integrated with published proxies from the same core and two additional cores from the abyssal Philippine Sea. The results exhibited noticeable variations in the abovementioned indicators, in correspondence to changes in the supply of terrigenous material. The continental slope deposition featured signals of strong physical erosion and chemical weathering of unconsolidated sediments on the exposed continental shelf during the Quaternary sea-level lowstands, which significantly contributed to increased terrigenous OM input and productivity and, in turn, decreased bottom-water oxygenation and atmospheric CO 2 concentrations. In the abyssal Philippine Sea, increased Asian dust-driven OM input and productivity also acted as a sink of atmospheric CO 2 during sea-level lowstands. Analysis of the data suggested that the enhanced terrigenous OM input and biological pump and thus the decreased dissolved oxygen level of the bottom water on the western margin of the WPWP played important roles in modifying the global carbon cycle during sea-level lowstands. In contrast, the influence of hydrological dynamics on terrigenous OM input, productivity, and redox conditions therein during the Quaternary was limited. • First integrative OM and productivity study on the western margin of the WPWP. • Enhanced terrigenous OM input and productivity occurred during sea-level lowstands. • The studied area was an important sink for atmospheric CO 2 during sea-level lowstands. [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]