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Beach ridges and spits along the north-facing coast of the Chukchi Sea record paleo-storm history during the 1st millennium AD, correlative with a widespread global cooling climate episode. Northwest Alaska is a sensitive proxy owing to its absence of tectonism, glacio-isostasy, and a low rate of eustatic sea level rise. Four locales provide a regional transect and detailed chronologies: north-facing Deering and Cape Espenberg and west-facing Kotzebue and southwest facing Point Barrow. A single storm or series of storms during AD 400–600 impacted both north and south areas, while lesser intensity storms occurred across the southern region during the 11th century AD. The first millennium AD storms were as strong as or stronger than those of the 20th century, if paleo-sea level is factored in. Storm-heightened upwelling had a salubrious effect on cultures around the Chukchi Sea, leading to a florescence of whaling and walrusing.

Much of the global cooling during ice ages arose from changes in ocean carbon storage that lowered atmospheric CO2. A slew of mechanisms, both physical and biological, have been proposed as key drivers of these changes. Here we discuss the current understanding of these mechanisms with a focus on how they altered the theoretically defined soft-tissue and biological disequilibrium carbon storage at the peak of the last ice age. Observations and models indicate a role for Antarctic sea ice through its influence on ocean circulation patterns, but other mechanisms, including changes in biological processes, must have been important as well, and may have been coordinated through links with global air temperature. Further research is required to better quantify the contributions of the various mechanisms, and there remains great potential to use the Last Glacial Maximum and the ensuing global warming as natural experiments from which to learn about climate-driven changes in the marine ecosystem.

Aim Past pollen records reveal the changes in latitudinal distribution of plants in relation to climate, particularly their expansion in response to global warming. The maximum northward expansion of the mangrove genus Avicennia since the Early Eocene is known, but this information is missing for other mangrove taxa. Here, we evaluate the diversity of past mangroves with respect to latitude during three Cenozoic thermal maxima (PETM: 56 Ma; EECO: 54–49 Ma; MMCO: 17–14 Ma). Location North Atlantic, Mediterranean. Taxa Avicennia, other mangrove taxa (Rhizophoraceae, Nypa, Xylocarpus, Pelliciera, etc.). Method We collected well-dated marine sediments along a Northern Hemisphere latitudinal transect and we analysed their pollen content in order to compare the past distribution of mangrove taxa with the present. The analysis of 89 samples (PETM: 13; EECO: 31; MMCO: 45) was performed and interpreted using a robust botanical background for identification of pollen grains and their representativeness in marine sediments. Results During the Early Eocene, two palaeolatitudinal thresholds at 65–70°N and 35°N, respectively, delimited the Avicennia-only mangrove from a diversified but scrawny mangrove and finally from a diversified and well-developed mangrove. The Avicennia threshold was selective at 40°N during the Mid-Miocene. The Avicennia range limit was up to 10–15° poleward of the limit for other mangrove taxa during the Early Eocene and the Mid-Miocene compared with 9° at present. Main conclusions A buffer zone characterised by a diversified but scrawny mangrove co-occurring with a few megathermal plants occurred in the Early Eocene between 35°N and 65–70°N. This finding questions the relative influence of a more ‘equable’ climate and/or the ability of some taxa to expand towards areas with cooler conditions in the past. Mangrove provincialism, which was established progressively after the Early Eocene, was probably forced by plate tectonics. The taxonomic impoverishment of the Atlantic East Pacific province was probably caused by successive periods of global cooling. These results support the Tethyan origin of the mangroves.

Considered as one of the most significant climate reorganisations of the Cenozoic period, the Eocene-Oligocene Transition (EOT; ca. 34.44–33.65) is characterised by global cooling and the first major glacial advance on Antarctica. While in the southern high-latitudes, the EOT cooling is primarily recorded in the marine realm, the extent and effect on terrestrial climate and vegetation is poorly documented. Here, we present a new, well-dated, continuous, high-resolution palynological (sporomorph) data and quantitative sporomorph-based climate estimates recovered from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene (37.97 Ma) to early Oligocene (33.06 Ma). Our results indicate three major climate transitions and four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) a warm-temperate Nothofagus-Podocarpaceae dominated rainforest with paratropical elements from 37.97–37.52 Ma; (ii) cool-temperate Nothofagus dominated rainforest with secondary Podocarpaceae rapidly expanding and taking over regions previously occupied by the warmer taxa between 37.306–35.60 Ma; (iii) fluctuation between warm temperate – paratropical taxa and cool temperate forest from 35.50–34.49 Ma, followed by a cool phase across the EOT (34.30–33.82 Ma); (iv) post-EOT (earliest Oligocene) recovery characterised by a warm-temperate forest association from 33.55–33.06 Ma. Coincident with changes in stratification of water masses and sequestration of carbon from surface water in the Southern Ocean, our sporomorph-based temperature estimates between 37.52 Ma and 35.60 Ma (phase ii) showed 2–3 °C terrestrial cooling. The unusual fluctuation between warm and cold temperate forest between 35.50 to 34.59 Ma is suggested to be linked to the initial deepening of the Tasmanian Gateway allowing eastern Tasmania to come under the influence of warm water associated with the proto-Leeuwin Current (PLC). Further to the above, our terrestrial data show mean annual temperature declining by about 2 °C across the EOT before recovering in the earliest Oligocene. This phenomenon is synchronous with regional and global cooling during the EOT and linked to declining pCO2. However, the earliest Oligocene climate rebound along eastern Tasmania is linked to transient recovery of atmospheric pCO2 and sustained deepening of the Tasmanian Gateway, promoting PLC throughflow. The three main climate transitional events across the studied interval (late Eocene–earliest Oligocene) in the Tasmanian Gateway region suggest that changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation dynamics, but a series of regional and global events, including a change in stratification of water masses, sequestration of carbon from surface waters, and changes in pCO2 may have played vital roles.

The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition., Plain Language Summary: The South Asian or Indian monsoon affects the lives of billions. Through the erosion and weathering of rocks, the monsoon also has the potential to remove carbon dioxide from the atmosphere through increased weathering in the region including the Himalaya Mountains. The late Miocene, between 9 and 5 million years ago, was a period of global cooling and proliferation of grasslands in different regions including South Asia. Here, we examine the composition of clays formed by rock weathering during the late Miocene to determine their source region around the Bay of Bengal. The results suggest a generally stable mixture of sources with the strongest sources being regions with the highest monsoon rainfall today. We identify slight changes in the mixture of sources, which accompany a global change in carbon cycling, highlighting the role monsoon climate likely played in these changes. Toward the end of the Miocene, we identify a change in the Sr isotopes, which was not caused by source changes but by the strength of the rock weathering. This change has been observed in global records and it seems likely that it was driven by rock weathering in the South Asian Monsoon region., Highlights: Radiogenic isotope compositions of detrital clays from the Bay of Bengal indicate a generally stable provenance from 9 to 5 Ma. A step change in Nd and Pb isotope compositions at ∼7.3 Ma reflects a climatically driven eastward shift in precipitation patterns resulting in enhanced erosion of the Indo‐Burman Ranges. Elevated 87Sr/86Sr between 6 and 5 Ma was likely related to increased chemical weathering caused by thicker soils and by C4 plant expansion., DFG, ANR, IODP

The Frasnian–Famennian biotic crisis (~372 Ma) was one of the “big five” mass extinction events in the Phanerozoic. This event was associated with dramatic climatic and oceanographic perturbations, including oceanic anoxia, global cooling, sea-level fluctuations. Large-scale volcanic activity is one of several possible triggers that have been suggested as the ultimate cause of this crisis, based on Hg enrichment data from widespread sections. However, there are also sections that do not show a Hg enrichment across the Frasnian–Famennian boundary. To further investigate the hypothesis of a volcanic trigger for the Frasnian–Famennian mass extinction event, mercury (Hg) analyses were performed on six North American records (five from the Appalachian Basin and one in the Illinois Basin) that include the Frasnian–Famennian boundary. There is no uniformly observed Hg enrichment at or below the Frasnian–Famennian boundary across the six sites. A potentially volcanically driven Hg anomaly is found in the Illinois Basin; however, the Hg enrichment occurs stratigraphically above the Frasnian–Famennian boundary. Mercury records from the studied sites question the timing of the volcanism that may be responsible for the mass extinction event. Further studies are needed to fully understand the geographic distribution and eruption history of the large igneous provinces, as well as the link between Hg and volcanism during the Frasnian–Famennian interval.

Palaeo-oceanographic reconstructions indicate that the distribution of global ocean water masses has undergone major glacial–interglacial rearrangements over the past ~2.5 million years. Given that the ocean is the largest carbon reservoir, such circulation changes were probably key in driving the variations in atmospheric CO2 concentrations observed in the ice-core record. However, we still lack a mechanistic understanding of the ocean’s role in regulating CO2 on these timescales. Here, we show that glacial ocean–sea ice numerical simulations with a single-basin general circulation model, forced solely by atmospheric cooling, can predict ocean circulation patterns associated with increased atmospheric carbon sequestration in the deep ocean. Under such conditions, Antarctic bottom water becomes more isolated from the sea surface as a result of two connected factors: reduced air–sea gas exchange under sea ice around Antarctica and weaker mixing with North Atlantic Deep Water due to a shallower interface between southern- and northern-sourced water masses. These physical changes alone are sufficient to explain ~40 ppm atmospheric CO2 drawdown—about half of the glacial–interglacial variation. Our results highlight that atmospheric cooling could have directly caused the reorganization of deep ocean water masses and, thus, glacial CO2 drawdown. This provides an important step towards a consistent picture of glacial climates.

Early Paleogene neodymium (Nd) isotopic reconstructions of ocean circulation in the Pacific suggest a bipolar mode of overturning circulation characterized by convection of deep-water masses from 70 to at least 40 Ma. This mode is fundamentally different from the “sluggish, diffusive” mode that characterizes the modern North Pacific. Therefore, major reorganization of Pacific circulation must have occurred between 40 Ma and the modern. To investigate the potential timing of such a reorganization, we present new Nd isotope data from drill sites spanning 40 to 10 Ma. Here, we use Nd isotopic analyses to identify the sources of dissolved Nd to the Pacific in order to evaluate the application of the Nd proxy for ancient water mass composition. We combine analyses of fossil fish debris, sequentially leached oxide coatings and leach residues to further refine our understanding of Nd marine geochemical cycling and to contribute new constraints on the paleoceanographic history of the Pacific. Overall, these data support previous interpretations of the convection of deep water in the Pacific sector of the Southern Ocean and surface-ventilated North Pacific Deep Water formation from ∼70 to 40 Ma. The new Nd isotope data suggest a gradual transition between 36 and 25 Ma, a time period characterized by global cooling. This transition consists of a change from North Pacific Nd isotopic signatures controlled by convection and water mass mixing to values heavily influenced by overprinting from other sources of Nd to the deep Pacific. Such a transition is consistent with a change in overturning circulation from a “Paleogene mode” to a mode dominated by sluggish diffusive mixing. After 25 Ma the data indicate a significant contribution of radiogenic dissolved Nd to the deep waters of the North Pacific. The most likely source of radiogenic dissolved Nd would have been labile volcanic ash that altered the composition of the water mass as it slowly advected through the North Pacific. A slowing of overturning circulation in the North Pacific could have resulted in diminished poleward heat transport, increasing equator to pole thermal gradients and contributing to a cooling global climate.

In this paper, we provide a late Miocene (Tortonian) to early Pleistocene (Gelasian) palynological record from the Eryuan Basin, Yunnan Plateau, China, to investigate plant diversity over this time. Between 7.6 and 4.3 Ma, the palynological assemblage was dominated by coniferous trees (70.2% on average), with subordinate amounts of broadleaved trees (8.8% on average). This suggests that the vegetation mainly comprised mixed forests, and that the climate was relatively warm and humid. After 4.3 Ma, the proportion of conifer pollen increased overall, and amount of cold-temperate coniferous forest Picea and Abies pollen, in particular, increased significantly (from 19.1% to 41.9%), concurrent with decreases in the pollen of broadleaved trees, shrubs, herbs, and other plant taxa. We suggest that these plant variations and overall reduced diversity may be responses to the tectonic uplift of the Yunnan Plateau and global cooling.

The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures., Proxies of deep circulation suggest that the onset or strengthening of the Atlantic meridional overturning circulation occurred at the Eocene-Oligocene Transition. The authors show, using a paleoclimate model of the late Eocene, that a shift from Pacific to Atlantic overturning can be triggered at this time by closing the Arctic–Atlantic gateway.

A large fossil leaf assemblage (>3700 specimens) is reported from the Oligocene Rio Leona Formation in the Sierra Baguales of Chilean Patagonia. The association comprises 29 species but is dominated by Nothofagus genera, which constitutes 65% of specimens. The collection can be classified as a Mixed Palaeoflora of the Austral-Antarctic association. Stratigraphic analysis of the assemblage indicates a decrease in species diversity and richness over time, which was accompanied by species turnover. Quantitative studies of foliar morphology (CLAMP, Leaf Margin Analysis) indicates cool-to-cold and dry climatic conditions, with a Mean Annual Temperature of 9.2 °C, a relatively high seasonality in temperature and precipitation, and a Mean Annual Precipitation of 931 mm. Nothofagus only became dominant in southeastern Patagonia during the Rupelian, coinciding with a marked global cooling period linked to the initiation of glaciation in Antarctica about 34 Ma. The decrease in precipitation following this event is attributed to the development of a rain shadow to the east of the rising Southern Patagonian Andes, which must have been of the order of 1000 m or more for topographic climate forcing to take effect. This contrasts with the rain shadow development east of the Andes at lower latitudes, which was mainly manifested after the middle Miocene.

Aeolian dust input exerts significant influence on oceanic biogeochemical cycles and further potentially controls atmospheric CO2 concentrations. However, the possible link between long-term aeolian dust supply and primary productivity in the western North Pacific remains poorly understood. Here, we present a comprehensive study of major and trace elements and total organic carbon (TOC) concentrations of sediments from Integrated Ocean Drilling Program (IODP) Site U1430 in the southern Japan Sea, in order to reconstruct oceanic palaeoproductivity evolution and test its possible link to Asian dust input since 4 Ma. Palaeoproductivity proxies indicate remarkable increases in productivity at ∼3–2 Ma followed by high-frequency oscillations in productivity since 1.2 Ma. We suggest that higher dust-derived iron supply from Central Asia at 3–2 Ma, which was likely driven by the growth of the Northern Hemisphere ice sheets, could account for enhanced primary productivity and export production in the Japan Sea. Such increased oceanic palaeoproductivity could enhance organic carbon burial, which might contribute to the decrease in atmospheric CO2 concentrations, and provide a positive feedback to the global cooling. However, the Tsushima Warm Current (TSWC) intrusion via the southern Tsushima Strait, which was controlled by glacioeustatic sea level changes, has been the principal cause of the rapid changes in primary productivity and benthic redox condition since 1.2 Ma, regardless of continuously increased Asian dust input.

Circulation more than temperature Changes in continental configuration and sea level affected the ocean's oxygen levels and the rate of denitrification between 70 and 30 million years ago. That finding by Kast et al. shows a fundamental difference from the modern ocean, in which the extent of suboxia is controlled primarily by global temperature. Changes in the nitrogen isotopic composition of marine organic matter correlate with the collision of India and Asia and the circulation changes that occurred as a result. Later, isotopic composition changed further in response to a fall in sea level as global cooling caused ice sheets to grow. Science , this issue p. 386

The Eocene is an enigmatic and interesting period due to the critical thermal events that occurred during the gradual global cooling, which have been demonstrated in the marine realm but remain poorly reported in terrestrial basins. In this study, a continuous ~404-m interval of the Middle Eocene terrestrial succession in Bohai Bay Basin, eastern China, was recovered from Well Fanye-1 in the Shengli Oilfield. This interval provides a unique record that can be used to better clarify the terrestrial sedimentary responses to astronomically forced climate changes, especially the Middle Eocene Climatic Optimum (MECO). Here, a high-resolution cyclostratigraphic framework from the lower third member (Es3l) to the upper fourth chun member (Es4cu) of the Shahejie Formation (Middle Eocene) was constructed by using magnetic susceptibility (MS) as a palaeoenvironmental proxy, in association with new paleomagnetic data. Power spectral analysis of the MS series reveal that the wavelength ratios of stratigraphic cycles are ~43.1–25:15.3–7.5:4.5–3:2.2–1.4, consistent with the period ratios of astronomical cycles. Moreover, a high-resolution astronomical time scale (ATS) for Well Fanye-1 was established by tuning the MS curves to the astronomical solution in combination with the magnetic stratigraphic framework. The method for establishing a high-resolution ATS with magnetostratigraphy and cyclostratigraphy was well applied in Well Fanye-1, making it possible to recalculate the ages in the Jiyang Depression. Finally, the terrestrial record across the MECO event was constructed and characterized based on the widespread “interbedded” argillaceous limestone. The resulting record is consistent with the time frame based on marine records and highlights the apparently primary role of the MECO event in shaping Asian paleoenvironments.

The characteristics of the evolution of the South Asian monsoon during the late Miocene through the Pliocene are highly debated. To obtain a better understanding, we studied the clay mineral assemblages and the clay fraction content of a high-quality sedimentary sequence (borehole core ZK1) spanning the interval of 8.8–2.62 Ma in the Zhaotong Basin, southwestern Yunnan Province, on the southeastern margin of the Tibetan Plateau. Smectite, kaolinite, illite and vermiculite were the four main clay minerals identified, and changes in their relative abundance reveal a distinct pattern of climate change during the study interval. Until the very late Miocene kaolinite and smectite, with a small amount of illite, were dominant, suggesting a relatively warm and humid climate; from ~6.2 to ~2.8 Ma smectite was dominant, with a minor amount of kaolinite and illite, indicating a relatively cool and humid climate; and from ~2.8 to 2.62 Ma vermiculite (HIV) and illite were dominant, with a minor amount of kaolinite, indicating a relatively cold and humid climate. The variation in clay mineral assemblages indicate substantial changes in the South Asian monsoon in the Zhaotong Basin that promoted a change from a warm and humid climate in the late Micoene to cool and humid climate in the very late Miocene through Pliocene, followed by a gradual trend towards a cold and humid climate in the very late Pliocene. Comparison with records from elsewhere indicates that the observed variations in the South Asian monsoon were mainly controlled by global cooling rather than by Tibetan Plateau uplift.

Two competing factors, the global cooling and the uplift of Tibetan Plateau, have been proposed to drive the central Asian aridification, but their relative role has seldom been discriminated in paleoclimate and paleoenvironment records. Here, we reconstruct a 14-million-year-long record of paleohydrology and paleoecology in the western Qaidam Basin by applying the compound-specific hydrogen (δ2H) and carbon (δ13C) isotope analyses to terrestrial leaf wax long-chain n-alkanes. The δ2H values are low during the interval of 14.6 to 13.0 Ma. Then the δ2H increases from 13.0 to 12.2 Ma and maintains high values from 12.2 to 3.2 Ma with a peak high value of −156.1‰ at 8.0 Ma. After 3.2 Ma, the δ2H values are low and vary larger than 30‰. The δ13C values decrease from 14.6 to 13.0 Ma and are low from 13.0 to 3.2 Ma except a high value at 3.8 Ma. Then they decrease slightly after 3.2 Ma. Low δ2H values indicate relatively wet climate between 14.6 and 13.0 Ma. The decreasing δ13C values during the same time period support the ecologic shift with the decline of warm component of conifers after the Mid-Miocene Climatic Optimum. High δ2H values since 13.0 Ma are synchronous with the uplift of northern Tibetan Plateau, implying tectonics-driven aridity. Large-amplitude variation in δ2H values since ca. 3.2 Ma seen in East and West Qaidam and lower δ13C values reveal the climatic cyclic responses to the Northern Hemisphere Glaciation.

The development of larger and longer lasting northern hemisphere ice sheets during the mid‐Pleistocene Transition (MPT) coincided with global cooling. Here, we show that surface waters of the north‐eastern Atlantic actually warmed across this interval (∼1.2–0.8 Ma), which we argue reflects an increase in the north‐eastward transport of heat and moisture via the North Atlantic Current (NAC) into the Nordic Seas (the Atlantic Inflow). We suggest that simultaneous cooling and warming along the north‐western and south‐eastern margins (respectively) of the NAC during Marine Isotope Stage 28 (∼995 ka) reflected the increasing persistence of northern ice sheets as Atlantic Inflow increased. This resulted in a diachronous shift from ∼40 to ∼100 kyr cyclicity across the North East (NE) Atlantic as the growing influence of northern ice sheets spread southwards; to the north‐west of the NAC the first “100 kyr” cycle preceded Termination 12 (∼960 ka), while on the south‐eastern margin of the NAC the transition occurred ∼100 kyr later. Exploratory climate model simulations suggest that increasing Atlantic Inflow at this time could have accelerated ice sheet growth because pre‐existing moderately sized ice sheets allowed the positive effect of increasing precipitation to outpace melting. In addition, we propose that the dependence of post‐MPT ice sheets on moisture transport via the Atlantic Inflow may ultimately contribute to their apparent vulnerability to insolation forcing once a critical size threshold is crossed and high latitude ice sheets become starved of a vital moisture source.

The development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation., Key Points: Relatively stable mixture of source rocks weathered to clays over the past 27 Myrs Pronounced increase in primary clay minerals occurred 13.9 Myrs ago Shift in weathering regime possibly result of winter monsoon dry season development

Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.

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Highlights: • A quantitative record of Miocene EASM from northern China was obtained. • The EASM stepwise decreased from ~17.1 Ma to 7.4 Ma and increased after ~7.4 Ma. • Middle Miocene EASM evolution is mainly regulating by temperature changes. • Palaeogeography play a key role in controlling the evolution of late Miocene EASM. Abstract The East Asian summer monsoon (EASM) precipitation is vital to hydrology, ecology and societal activities in the densely populated region of East Asia. However, its long-term evolution history and driving forces during the relatively warm Miocene remain unclear, even conflicting in some intervals. Here, we present a new, and quantitative record of EASM precipitation during Miocene using the Bayesian approach of Climate Reconstruction Software (CREST) based on pollen flora from the Tianshui Basin located on the northwestern Tibetan Plateau (TP). The results demonstrate that a strong and relatively stable EASM precipitation period occurred during the Neogene in northern China at ~17.1–13.6 Ma, which was followed by a strong and gradual decreasing period between ~13.6 and 7.4 Ma. This trend was abruptly stopped at ~7.4 Ma with the beginning of a period of large amplitude precipitation increase. The comparison analysis reveals that the gradual decrease of EASM precipitation during the period of ~17.1–7.4 Ma was primarily controlled by the global cooling, whereas the significant increase period after ~7.4 Ma was mainly related to the late Miocene uplift of the TP, supporting climate model simulations, in which both the global temperature and palaeogeography play important roles in regulating the long-term evolution of EASM precipitation.

Soil respiration (Rs), the production of carbon dioxide in soils, increases dramatically from deserts to forested ecosystems. Rs values thus provide a potential tool to identify past ecosystems if recorded in sedimentary archives. Here, we propose a quantitative method to reconstruct past Rs values from paleosols. This method reverses the soil paleobarometer, a proxy that estimates past atmospheric CO2 concentration values (CO2atm) from paleosols while considering a narrow range of variation for Rs. We use past CO2atm values from marine proxies to reconstruct soil respiration from a 20 million year-long isotopic record from northeastern Tibet covering the transition from the Eocene greenhouse to the Oligocene icehouse. We show that Rs dropped at least 4-fold through the transition into the Oligocene icehouse, marking the spread of boreal desert-steppes of Central Asia. We show that increasing aridity and the decline of monsoonal rainfall, in parallel with global cooling, caused the fall of soil respiration. These highly dynamic Rs emphasize the need for a systematic screening of paleosol isotopic data before using the soil paleobarometer to reconstruct CO2atm

Super greenhouse temperatures at the onset of the Cenomanian‐Turonian oceanic anoxic event (OAE 2) have been widely linked with large igneous province (LIP) volcanic activity. However, the extent to which volcanism influenced subsequent climate changes throughout OAE 2, such as global cooling during the Plenus Cold Event (PCE) early in the OAE, and the subsequent return to very warm conditions through the second part of the crisis remain less clear. Here, new osmium‐isotope (187Os/188Os) data are presented from the northeastern margin of the proto‐North Atlantic Ocean (ODP Leg 174AX Bass River, NJ, USA). The results are consistent with previously published OAE 2 records and are similarly interpreted as documenting LIP activity while further demonstrating the ability to use osmium‐isotope stratigraphy as a global chemostratigraphic marker in open‐ocean records. Correlations of 187Os/188Os and sea‐surface temperature trends at Bass River and other sites show that the earliest PCE cooling coincided with intense volcanism, but that LIP activity began to decline during or soon after the cold pulse. These temporal relationships support previous hypotheses that the PCE was regionally diachronous and likely caused by enhanced carbon sequestration via organic‐matter burial and silicate weathering, rather than a period of volcanic quiescence, while the persistently warm conditions later in OAE 2 were linked to reduced silicate weathering rather than sustained volcanism. These findings highlight the complex interactions between LIP emplacement and climate responses during OAE 2, reemphasizing the need for similar correlations between volcanism and paleotemperature proxy data for other major events in Earth's history.

Late Cenozoic changes in chemical weathering and the dust cycle in response to the regional aridification and global cooling in the tectonically active northern Tibetan Plateau is an intriguing issue, although it remains poorly understood. The change in the 87Sr/86Sr ratio of basin water is linked to variations in the overall input of various Sr sources with different 87Sr/86Sr ratios, and analyses of such changes can be a useful tool for revealing changes in regional lithology, weathering regimes and the dust cycle linked to tectonics and climate. In this study, we collected fossil shells of ostracods and gastropods from the Miocene Dahonggou section to reconstruct the paleolake water 87Sr/86Sr ratio from 14.8 Ma to 11.1 Ma in the northern Qaidam Basin on the northeastern Tibetan Plateau. The reconstructed paleolake water 87Sr/86Sr ratios based on fossil shells and bulk carbonates from sediments display a coincident and stable 87Sr/86Sr ratio of approximately 0.7115, which did not show any detectable change in response to the enhanced aridification since ~13 Ma as inferred by the ostracod assemblage and its stable carbon and oxygen isotopes. The results indicate that the Sr influx regime from various sources did not change significantly during the aridification processes ~13 Ma, which may have been caused by a less detectable change in proportion of silicate versus carbonate weathering, and/or an overwhelming Sr source (e.g., extrabasinal eolian dust) that occurred from 14.8 Ma to 11.1 Ma. Further, the 87Sr/86Sr ratios of modern lake water and river sand carbonates in the study region are significantly higher, approximately ≥0.001, than those of the Miocene lake water. This observation can be explained by two possible mechanisms that need to be tested in the future: 1) given a Miocene Sr input regime that is similar to today, a large contribution from some extrabasinal Sr source (e.g., eolian dust) with a much lower 87Sr/86Sr ratio is expected to have prevailed from 14.8 Ma to 11.1 Ma but is absent in the modern setting or 2) given a Miocene Sr input regime that could yield an overall lower lake water 87Sr/86Sr ratio of approximately 0.7115, a significant increase in the 87Sr/86Sr ratio of catchment-scale Sr source may have occurred after 11 Ma in response to the uplift of the Qilian Mountains, which would have enhanced hydrothermal activity, metamorphism, glaciation and landslide processes, thereby resulting in more-radiogenic Sr source. Our study suggests that reconstructions of river/lake water 87Sr/86Sr ratios can place powerful constraints on the complex interactions among tectonics, climate and landscape evolution in the northeastern Tibetan Plateau based on a new perspective.

The Miocene Climatic Optimum (MCO, 14–17 Ma) was ~3–4 °C warmer than present, similar to estimates for 2100. Coincident with the MCO is the Monterey positive carbon isotope (δ13C) excursion, with oceans more depleted in 12C relative to 13C than any time in the past 50 Myrs. The long-standing Monterey Hypothesis uses this excursion to invoke massive marine organic carbon burial and draw-down of atmospheric CO2 as a cause for the subsequent Miocene Climate Transition and Antarctic glaciation. However, this hypothesis cannot explain the multi-Myr lag between the δ13C excursion and global cooling. We use planktic foraminiferal B/Ca, δ11B, δ13C, and Mg/Ca to reconstruct surface ocean carbonate chemistry and temperature. We propose that the MCO was associated with elevated oceanic dissolved inorganic carbon caused by volcanic degassing, global warming, and sea-level rise. A key negative feedback of this warm climate was the organic carbon burial on drowned continental shelves., In this study, the authors use planktic foraminiferal data to reconstruct ocean carbonate chemistry and temperature from 16.5 to 11 Ma from a size in the tropical eastern Indian Ocean to look at the causes of the Monterey Excursion (ME). They find a positive relationship between dissolved inorganic (DIC) carbon and the ME and a negative one for DIC and the carbon maxima events.

The South China Sea (SCS) is connected to the West Pacific through a deep channel in the Luzon Strait. Thus the SCS deep water is sensitive to the evolution of Pacific Ocean circulation, which significantly influences the global climate system. Geochemical data (Pb isotope and redox-sensitive elements data) and magnetic data were determined for a Fe–Mn nodule obtained from Jiaolong seamount in the central SCS. These records reflect interactions between changes in ice sheets, deep Pacific circulation, and weathering inputs to the deep SCS during the Pliocene and Quaternary. Our results show that the SCS deep-water environment can be divided into three major Stages (Stages 1–3). Stage 1 (∼4.8–1.4 Ma) was characterized by a well-oxygenated Pacific Deep Water (PDW) and lower dust inputs; then moderate stable deep-water ventilation and greater inputs of Asian dust occurred during Stage 2 (1.4–0.9 Ma). During Stage 3 (

Poor understanding of the differential evolution of interglacial climate over various regions in Eurasia greatly limits our ability to predict the specific local impacts of future climate change. Here we demonstrate starkly opposing trends in interglacial intensities in Asia and Europe over the early Middle Pleistocene and Mid-Brunhes Transitions based on the study of various climate proxies in the Paks loess record (Hungary), a key profile in the European Loess Belt. These contrasting climate trends imply major but unexplained differences in the regional response of Quaternary climate to shifts in forcing mechanisms during two major reorganizations of Earth's climate across Eurasia. Using new rock magnetic datasets from the Paks record we suggest that the changing dominance of Mediterranean, Atlantic (Westerlies) and continental air masses under the influence of the quasi permanent high pressure centres over the Fennoscandian ice sheet played a key role in the observed differences in the evolution of early Middle Pleistocene climate. We also propose that the intensification of the early Middle Pleistocene glaciation of Central Asian mountains may have strengthened and shifted the Siberian High westward on multi-millennial/orbital timescales, which in turn forced geographically contrasting expressions of the MIS 19 to 11 interglacials in Eurasia. This is the first coherent explanation for the geographically diverse response of regional climate to the early Middle Pleistocene climate transitions and points to the clear role of global cooling and expanded mid-latitude glaciers in driving these events.

We estimate global surface albedo from the areal proportion of land to sea in climatically-significant latitudinal belts at ten million-year intervals for the Late Cretaceous and Cenozoic (from 120 million years ago) using modern plate tectonic reconstructions and a composite apparent polar path designed to minimize known biases in the determination of paleolatitude. We find that global surface albedo stayed almost constant until it shifted 30% higher to the modern value of around 0.15 with the inception of the Late Cenozoic Ice Age 34 million years ago, reflecting polar ice-albedo amplification of global cooling resulting from the reduction of greenhouse gases below a critical threshold, most probably as the culmination of enhanced CO2 weathering consumption of continental mafic rocks in the equatorial humid belt. The contribution from cloud cover toward a planetary albedo is unclear in the absence of measurable proxies but might eventually be gauged from the role cloudiness evidently plays in maintaining radiative balance with the increasing land bias between northern and southern hemispheres over the Cenozoic.

The Quaternary loess–paleosol and underlying Neogene red clay sequences on the Chinese Loess Plateau (CLP) contain a remarkable continental record of past East Asian monsoon changes and aridification of the Asian interior. While monsoon variability during the Quaternary is reasonably well understood, the evolution and dynamics of the monsoon during the Neogene are still debated. The rock magnetism of aeolian sediments is a well-established tool for reconstructing the palaeoclimatic history of Asia. Here, we present a rock magnetic record from Late Neogene red clay sediments of the Chaona section in the central CLP. The results indicate that the main magnetic minerals in the red clay are magnetite, maghemite, hematite and goethite, similar to the overlying Quaternary loess-palaeosol sequences. The high-resolution rock magnetic record, combined with the results of other proxies, demonstrate a stepwise intensification of the summer monsoon and a progressive enhancement of the winter monsoon in East Asia during the Late Neogene. Based on the results, the climatic evolution of East Asia can be divided into three intervals: Interval III, from 8.1 to 6.8 Ma, is characterized by a cool, dry climate with a relatively weak East Asian Summer Monsoon (EASM) and East Asian Winter Monsoon (EAWM); Interval II, from 6.8 to 4.3 Ma, is characterized by cool/warm cycles; and Interval I, from 4.3 to 2.8/2.6 Ma, was warm and humid, and within which the EASM strengthened rapidly and the EAWM fluctuated considerably, with an increasing trend. We infer that before 4.3 Ma the variations of both the EASM and EAWM were closely related to global cooling and that the intensified EASM during the late Pliocene was primarily caused by tectonic events, including the gradual closure of the Panama Seaway and the uplift of the Tibetan Plateau, rather than by global cooling.

Geological evidence shows that the Asian inland environment experienced enhanced aridity from the Early to the Late Eocene. This enhanced Eocene aridity in the Asian inland was related to combined impacts from global cooling, topographic uplift and land–sea reorganization. However, the primary cause of the enhanced Eocene aridity in this region is still under debate and varies between global cooling and early Tibetan Plateau uplift. To distinguish between the importance of these factors, we evaluate the climatic impacts of these factors from a modeling point of view. Consistent with geological evidence, our simulations support the observed enhanced Eocene aridity in the Asian inland. Both global cooling (induced by atmospheric CO2 decrease) and topographic uplift contributed to intensified Asian inland aridity, while land–sea redistribution did not. The uplift of the central Tibetan Plateau during the early stage of the India–Asia collision is emphasized more to be responsible for the long-term Asian inland aridification during the Eocene, playing at least an equally important role as the global cooling induced by decrease in atmospheric CO2.

The transition from the extreme global warmth of the early Eocene ‘greenhouse’ climate to the present glaciated state is one of the most fundamental reorganizations of global climate known in the geologic record. The Middle to Late Eocene interval between 49 and 33 Ma was a globally important transition period from greenhouse to initial icehouse conditions. The Middle Eocene Climatic Optimum (MECO, ~ 40 Ma) was a transient period of global warming that interrupted the secular Cenozoic cooling trend. The Eocene-Oligocene transition (ca. 33.5 Ma) marks the first major decline in Cenozoic global temperatures and the initiation of Antarctic glaciation. However, a major challenge comes from recent investigations of plateau uplift processes and resulting environmental changes. The tectonic evolution of the Iranian plateau offers an explanation for global cooling during the Cenozoic, as a result of the gradual closure of the Neotethyan Sea, which led to the disappearance of the Indian Ocean-Mediterranean Sea connection, mountain building, extensional collapse, rifting, and flare-up type volcanism, erosion, and exhumation. Increasing topography by shortening as a result of subduction of the distal Arabian margin beneath the Iranian Plateau and contemporaneous exhumation of a metamorphic core complex between 49 and 33 Myr ago led to aridification of Iranian plateau and to the some elevation of the plateau. This rise in elevation is roughly contemporaneous with the emplacement of flare-up-type volcanics in the Urumiyeh-Dokhtar zone and over large portions of Central Iran. Peak volcanism occurred during the transient warming event MECO. New findings suggest that this global transition is linked to significant aridification and cooling in southwest Asia, and thus support the idea that global cooling is associated with the Eocene-Oligocene transition. The good match of tectonic deformation and uplift of the Iranian Plateau with climatic changes is significant.

The Eocene was an interval of climate evolution, when the extreme high temperatures of the earliest Cenozoic gave way to a global cooling trend. Fine-grained lacustrine sediments of Eocene age from northeastern China represent an excellent archive to study long-term environmental and climatic changes at high-resolution. The Huadian Basin is a Cenozoic, fault-bounded basin in Jilin Province, northeastern China. Though small in area, it contains numerous oil shale- and coal-bearing layers, which provide an abundant Middle to Late Eocene palynoflora. Eighty-five palynomorph genera and one hundred palynomorph species were identified in the Huadian Formation, allowing to distinguish 4 palynozones. The nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad-leaved forests during deposition of the Huadian Formation. Using the coexistence approach (CA), we calculated seven paleoclimatic parameters, which indicate a subtropical warm and humid climate with a mean annual temperature above 13.6 °C and a mean annual precipitation of at least 887 mm. However, the climate became cooler and drier during the transition from the lower Oil Shale Member to the upper Carbonaceous Shale Member. Palaeoclimatic data from the various Middle and Late Eocene basins of northeastern China (i.e., the Huadian, Fushun, Yilan, Hunchun and Jishu basins) were compared with data from North American and European basins. Middle Eocene climate in the Northern Hemisphere was generally warm and humid, and the mean annual temperature and precipitation in northeastern China were similar to those in North America, though slightly lower than those of Europe. Similar trends in temperature and precipitation on different continents support the existence of a global Mid-Eocene cooling event. This paper is the first systematic study of Middle to Late Eocene seasonality in the Huadian Basin. Our results show an apparent differentiation in both temperature and precipitation between summer and winter, supporting the view that the East Asian Monsoon was established in northeastern China already during the Middle to Late Eocene. This Middle and Late Eocene monsoon was likely driven by the development of Pacific trade winds and an alternating, seasonal high- and low-pressure system over Siberia. The climatic changes observed in our dataset, especially the precipitation changes, appear to have played an important role in controlling oil shale formation in the Huadian Basin. A warmer and more humid climate, with abundant precipitation and high subsidence rates, formed a deeper Huadian depositional lake. High productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation.

The world during the early Middle Triassic (Anisian) was characterized by a distinct recovery of the carbonate factory after the Permian–Triassic crisis. This recovery seems to have passed over the Anisian environment on the tropical northern margin of Gondwana (Israel, Levant Basin) and to have resulted in the low diversity of barren horizons of carbonate-secreting organisms. Four Anisian successions (the Ramon 1, Hameishar 1, Nafha 1, and David 1 boreholes) were studied to decode the factors preventing regional recovery. A multi-proxy analysis was performed on these boreholes, including the carbonate/siliciclastic ratio, total organic carbon (TOC), carbon/nitrogen (C/N) ratio and inorganic carbon (δ13Ccarb), oxygen (δ18Ocarb), and nitrogen (δ15N) isotopic compositions. The aim of assessing the combination of these proxies was to characterize the geochemical conditions in the regional basins. These successions record two C-cycle perturbation events, characterized by negative shifts in δ13Ccarb values and recognized in most successions, indicating the land-marine teleconnection effect on the C-cycle perturbation. The δ18Ocarb excursions revealed similar oscillation trends, with global warming evidenced by increasing circumtropical precipitation and terrestrial influxes, whereas global cooling was reflected by increased carbonate factory production. The low δ15N values in all of the studied successions indicated the presence and flourishing of N-fixers. The absence or scarcity of carbonate-secreting organisms suggests that these N-fixers were the source of the carbonate fraction in the sediments. Episodic events with high δ15N values suggest an accumulation of terrestrial organic matter (OM) or oxygenation events, allowing short-term colonization by benthic fauna at the marine sites.

An unusually short glaciation interrupted the warm Pliocene around 3.3 Ma (Marine Isotope Stage (MIS) M2). Different hypotheses exist to explain why this glaciation event was so pronounced, and why the global climate system returned to warm Pliocene conditions relatively quickly afterwards. One of these proposed mechanisms is a reduced equator-to-pole heat transfer, in response to a tectonically reduced Indonesian Throughflow (ITF). The ITF is a critical part of the global thermohaline ocean circulation, transporting heat from the Indo-Pacific Warm Pool to the Indian Ocean. When ITF connectivity is reduced, the water and heat supply for the Leeuwin Current, flowing poleward along Australia's west coast, is also diminished. To assess the possible relationship between mid-Pliocene glaciations and latitudinal heat transport through the Indonesian Throughflow, we constructed a multi-proxy orbital-scale record for the 3.7–2.8 Ma interval from International Ocean Discovery Program (IODP) Site U1463, off northwest Australia. The comparison of the Site U1463 record with paleoclimate records from nearby Site 763 and West Pacific Warm Pool Site 806 allows for a detailed regional reconstruction of Pliocene paleoceanography and thus for testing the proposed hypothesis. An astronomically-paced decrease in potassium content characterizes the late Pliocene interval of U1463. This record documents the increasing aridity of northwest Australia, periodically alleviated by reinforced summer monsoon precipitation under summer insolation maxima. The δ 18 O record of the planktonic foraminifer Globigerinoides sacculifer correlates exceptionally well with the sea surface temperature (SST) record from Site 806 in the West Pacific Warm Pool, even during MIS M2. Hence, Site U1463 preserves an uninterrupted ITF signal even during Pliocene glaciations. However, the U1463 δ 18 O G.sacculifer record exhibits a 0.5‰ offset with the nearby Site 763A record around MIS M2. This implies that Site 763A, about 500 km west of U1463, more closely tracks Indian Ocean SST records across MIS M2. The U1463 data reveal that heat-transport through the Indonesian Throughflow did not shut down completely during MIS M2, but rather its intensity decreased prior to and during MIS M2, causing Site 763A to temporarily reflect an Indian Ocean, rather than an ITF signal. We conclude that ITF variability significantly influenced latitudinal heat transport by means of the Leeuwin Current and hence contributed to the relative intensity of MIS M2. We propose the ITF valve between the Pacific and Indian Ocean as a positive feedback mechanism, in which an initial sea level lowering reduces ITF heat transport, in turn amplifying global cooling by advancing the thermal isolation of Antarctica.

The last hyperthermal event in the Eocene, the Late Lutetian Thermal Maximum or Chron C19r event, took place at ~41.5 Ma, during a long-term global cooling phase which occurred between the warm Early Eocene Climatic Optimum and the icehouse Oligocene Epoch. This paleoclimatic event was first identified in the Equatorial Atlantic Ocean Drilling Program (ODP) Site 1260 as an abrupt peak in bulk Fe content and a short-lived decline in stable isotopes (δ13C, δ18O) and carbonate content. Additional studies have recently been carried from the Southern Atlantic ODP sites 702 and 1263. However, many issues were not addressed at these deep-sea sites and no land-based record of the event had been studied. Therefore, the beach cliff at Cape Oyambre (N Spain) was analyzed with the aim of identifying the C19r event and investigating its paleoenvironmental impact. Using magnetostratigraphic and biostratigraphic information, the astronomically tuned cyclo-stratigraphic record from Oyambre was accurately correlated with ODP Site 1260. This, combined with stable isotope data, allowed identification of the event in a conspicuous dark marl bed. Given that the associated negative carbon isotope excursion extends for 2/3 of a precession-driven hemicouplet, a 7–11 kyr duration was estimated, which agrees with recent estimates from the Atlantic deep-sea sites. Exceptional insolation conditions were found to have accelerated the hydrological cycle, increasing rainfall and runoff on land and terrestrial sediment input to the sea, which resulted in relatively low carbonate content in the deep-sea sediments. The terrestrial input also caused seawater eutrophication and freshening, leading to low δ13C and δ18O values, increased abundance of autochthonous and reworked calcareous nannofossil taxa, peaks in the abundance of opportunistic Reticulofenestra

Climate and vegetation history from the Yucatan Peninsula, southeastern Mexico, are inferred from a mangrove sediment core deposited between the middle and late Holocene (~5600–1700 cal yr B.P.) in the Rio Hondo Delta. Fossil pollen and concentrations of Ca and Fe and Ca/Fe ratio in sediments are used to record changes in vegetation and climate. Palaeoecological and palaeoclimatic interpretations obtained from pollen abundances and associations and Fe/Ca ratio coincide with dynamics of major global forcings of climate change like ITCZ, ENSO and global cooling. Mesic conditions enabled tropical forest expansion during the middle Holocene (~5600–3650 cal yr B.P.), although there were periodic dry episodes at ~5200 cal yr B.P. and at ~4300 cal yr B.P. that caused disturbance and enabled herbaceous vegetation to expand. Changes in sedimentation and a gradual change from semi-evergreen to dry tropical forest occurred at ~3650 cal yr B.P., with increasing ENSO activity and southward migration of the ITCZ during transition of the middle to late Holocene. The driest period and lowest forest cover occurred between ~2600 and 2000 cal yr B.P. Data show that over the last two millennia, influence of the ENSO on southeastern Mexico is stronger compared to other proxy-records of climate variability from the Caribbean region.

Rising sea level in the coming century is of significant concern, yet predicting relative sea level change in response to eustatic sea level variability is complex. Potential analogues are provided by the recent geological past but, until recently, many sea level reconstructions have been limited to millennial scale interpretations due to age uncertainties and paucity in proxy derived records. Here we present a sea level history for the tectonically stable “far-field” Great Barrier Reef, Australia, derived from 94 high precision uranium–thorium dates of sub-fossil coral microatolls. Our results provide evidence for at least two periods of relative sea level instability during the Holocene. These sea level oscillations are broadly synchronous with Indo-Pacific negative sea surface temperature anomalies, rapid global cooling events and glacial advances. We propose that the pace and magnitude of these oscillations are suggestive of eustatic/thermosteric processes operating in conjunction with regional climatic controls.

The Early Mississippian K-O (Kinderhookian-Osagean) carbon isotope (δ13C) excursion or TICE (mid-Tournaisian carbon isotope excursion) is one of the most prominent positive δ13C excursions of the Phanerozoic. Recent studies raise uncertainties about the representative shape (single vs. double spikes) and magnitude of this δ13C excursion (3‰ to ≥ 6‰ in South China; ≥ 5.5‰ in Europe; and ≥ 7‰ in North America) and the 3‰ unidirectional increase in nitrogen isotopes across the δ13C excursion, which is unanticipated considering the amount of organic carbon burial required to form the δ13C excursion and the resultant oxygen increase and global cooling. To test if stratigraphic completeness and spatial isotope variations caused such uncertainties, we have conducted paired carbonate carbon (δ13Ccarb), organic carbon (δ13Corg) and nitrogen (δ15N) isotope analyses across the K-O interval in two well-exposed sections of the southern Great Basin, western United States. The two sections represent proximal shallow-water and distal deep-water depositional settings of a west-dipping carbonate ramp. In the distal ramp section where no exposure surface is present, both δ13Ccarb and δ13Corg show double spikes with peak δ13Ccarb values up to 7‰ and a negative shift down to 4‰ between the peaks. In the proximal shallower-water section where two karstic disconformities are observed, δ13Corg shows similar double spikes but δ13Ccarb displays only a single peak with the highest value of 5.5‰. The missing δ13Ccarb spike is likely caused by diagenetic alteration below a karstic disconformity that lowered δ13Ccarb but not δ13Corg values, resulting in smaller magnitude of the δ13Ccarb excursion. These features suggest that the 7‰ magnitude and double spikes are more representative of the K-O δ13C excursion in the southern Great Basin. The smaller magnitude of the K-O δ13Ccarb excursion in some sections of the Great Basin and the TICE in other sections globally may have overprinted with local environmental/diagenetic signal or resulted from stratigraphic hiatus/truncation, which needs to be clarified in future research. The δ15N across the K-O δ13C excursion in the distal ramp section is decoupled from δ13C, with the majority of δ15N values around 4 ± 1‰ that do not show any obvious temporal trend. In contrast, δ15N values in the shallow-water section is coupled with the K-O δ13C excursion, with a 3‰ positive shift from 4‰ to 7‰ at the rising limb of the δ13C excursion and a negative shift from 7‰ to 1–2‰ at the falling limb of the δ13C excursion. The δ15N trend from the distal ramp section is, in some extent, comparable with that documented from a section in South China, while the coupled δ13C–δ15N pattern in the proximal section seems better explain the potential redox change across a prominent δ13C excursion. Considering the sensitivity of δ15N to redox conditions of depositional environments, a more comprehensive δ15N study in a broader paleogeographic context is required to better understand the interactions between carbon and nitrogen cycles across the K-O interval—a critical transition from the mid-Paleozoic greenhouse clime to Late Paleozoic Ice Age (LPIA).

Late Miocene contourite deposits related to the paleo-Mediterranean Outflow Water (MOW) were identified in the Betic and Rifian corridors prior to the restriction of the Mediterranean-Atlantic gateway during the latest Miocene. In this study, we identified for the first time their downstream continuation in the Gulf of Cadiz through seismic stratigraphic analysis and the interpretation of contourite diagnostic features. The late Miocene contourite depositional system (CDS) consists of three stages (initial-, growth-, and maintenance-drift) which recorded the late Tortonian to early Messinian evolution from weak to vigorous bottom current flow in the Gulf of Cadiz prior to its cessation in the middle to late Messinian, represented by the buried-drift stage. Development of the CDS in the Gulf of Cadiz is coeval to a period when the continental margins were affected by regional deformation. Tectonism and diapirism, on top of sedimentary and climatic factors, exerted control on drift distribution and dimensions. However, dataset limitations hindered detailed analysis on the effect of deformation on CDS evolution. Overall, the long-term evolution of the late Miocene CDS across the Gulf of Cadiz towards the West Iberian margin suggests strengthening of paleo-MOW during the late Miocene which has significant impact on the North Atlantic ocean circulation and the late Miocene global cooling trend.

The Qaidam Basin in the northeastern part of the Tibetan Plateau preserves a continuous and thick Cenozoic sedimentary succession, which is of great significance to studying the aridification of inland Asia. Based on the normalized concentrations (element/Al) and chloride content records of the lacustrine sediments in deep drilling well SS9 in the western Qaidam Basin, the change in the aridity of inland Asia during the late Middle Eocene was investigated. The results show that the Al-normalized concentrations of Na and Cl, which are indicator elements of saline lake sediments, increased sharply at ~38 Ma. The peaks in the Ga/Al and chloride values indicate that the salinity of the lake was extremely high at ~38 Ma. Based on these results, the sudden decrease in the sedimentation rate, the chemical weathering index, the hematite content, and the (smectite + illite/smectite)/illite ratios, the Qaidam Basin experienced abrupt aridification during this period. The decrease in water vapor transport caused by the final retreat of the Paratethys Sea from the southern Tarim Basin may have been the main reason for the changes in the arid environment in the Qaidam Basin during the late Middle Eocene. Long-term global cooling and the uplift of the Altyn Tagh may have played a role in the background conditions.

Post-middle Miocene changes in climate and ecology in the northern Tibetan Plateau have been attributed to tectonic uplift and global climate change. However, the relative roles of tectonism and global climate change have been a long-standing debate. To untangle the complex influences of global climate change versus the tectonism on regional climate and ecology in the northern Tibetan Plateau, we studied carbon isotopes (δ13Cwax) of leaf wax long-chain n-alkanes and carbon (δ13C) and oxygen isotopes (δ18O) of carbonates from three stratigraphic successions (ca. 16 Ma to 2 Ma) in the Hexi Corridor (foreland basin) and compare them with paleoclimate records in the Qaidam Basin (intermontane basin). Our isotopic results can be divided into two stages. In Stage 1 (16–12 Ma), a decrease of δ13Cwax values in the Hexi Corridor and Qaidam Basin is synchronous with global cooling after the Mid-Miocene Climate Optimum (MMCO). We interpret the 2‰ decrease in δ13Cwax values to be associated with the decline in C4 plants due to the global cooling. In Stage 2 (since 12 Ma), plant carbon isotope discrimination (ƐCO2-wax) and δ18O values in the Hexi Corridor reflect relatively stable hydroclimate condition, which contracts with the enhanced aridity in Qaidam Basin during the same interval. We attribute the difference in paleohydrological conditions to the uplift-induced basin isolation and the enhancement of water deficiency in the Qaidam Basin. The effects of late Miocene uplift also manifest as persistent intra-basinal differences in the Hexi Corridor, indicating changes associated with orographic precipitation and ecology.

Changes in dinoflagellate assemblages indicate regional paleoceanographic events affecting western Colombia. Integration of palynomorph, planktonic foraminifera, and calcareous nannoplankton data from a 616 m thick outcrop section in the Ladrilleros-Juan Chaco region allows the construction of a detailed and reliable chronological framework and identification of marine high-productivity intervals. Results indicate marine deposition from middle (~15 Ma) to late (~10 Ma) Miocene. Dinoflagellate cyst assemblages are consistent with known regional assemblages and include more warm water taxa than cold ones. Correlation of the palynomorphs with the other microfossils studied allows calibration of the biostratigraphic ranges of seven species of dinoflagellate cysts commonly reported from tropical zones. The ratio between autotrophic and heterotrophic dinoflagellate cysts indicates an overall increase of paleoproductivity at ~13.8 Ma. Gonyaulacoid taxa dominate the lower interval (15–13.8 Ma), while peridinioid taxa dominate the upper segment (~13.8–10.5 Ma). This change coincides with the global cooling related to the growth of the Antarctic ice sheet (~14 Ma) and presumably increased the recurrence of events like La Nina in the equatorial Pacific. These conditions increased the primary productivity in the Pacific coastal region of northwestern Colombia, and four high-productivity intervals are tentatively correlated to the Mi3a, Mi-3b, Mi-4, and Mi-5 isotope events.

The Asian Summer Monsoon (ASM) is the dominant climate system of South and East Asia. However, the history of monsoon intensification and the driving forces behind it are controversial. Wind-blown sediments in mid-latitude East Asia and fluvial-derived sediments in the northern South China Sea imply contrasting ASM patterns during the late Cenozoic. Here we use pollen records from the southwest South China Sea (International Ocean Discovery Program (IODP) Site U1433) to reconstruct the ASM evolution in low-latitude Southeast Asia. A slow increase in herbaceous plants since 8 Ma indicates a persistent weakening of precipitation in Indochina, which is dominated by the ASM. This signal is closely associated with a consistent coniferous plant record, indicating a continuous cooling trend that correlates well with Sea Surface Temperature (SST) decrease in the west Pacific Ocean. We propose that the monsoon weakening resulted in as much as a ~ 25% reduction in precipitation over the past 8 Ma in response to the Northern Hemisphere glaciation/global cooling, with some of the increase in conifers being linked to uplift of the Vietnamese Central Highland and the SE flank of the Tibetan Plateau in Yunnan and northern Vietnam.