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The Saharo-Arabian desert is part of the largest near-continuous chain of drylands stretching from north-western Africa to the northern China. This harsh and often hyper-arid belt acts as a transition zone separating major biogeographic realms, including the Palearctic, Afrotropics and Indomalayan. This aridity is thought responsible for the creation of unique geographic endemism between Africa and Eurasia. However, there are no direct hydroclimate records from the Arabian hyper-arid interior before the mid-Pleistocene, leaving the terrestrial hydroclimate and the role of Arabia as a biogeographic crossroads or barrier largely unknown.We use desert speleothems preserved from the northern Arabian interior to identify past humid phases over the last 8 million years. These are particularly useful terrestrial climate archives as they act as underground rain gauges, requiring a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Our data reveal evidence of multiple ‘windows of opportunity’ of climate amelioration, allowing biogeographic exchange and dispersals to occur across the Arabian hyper-arid zone. Further, the novel analyses of the isotopic composition (d18O and d2H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal the diminishing influence of tropical rain-belt precipitation in Arabia across Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. The extent of Arabian aridity may thus be important in controlling biogeographic dispersals through the Arabian corridor, becoming increasingly less favourable through time. This is supported by fossil evidence which suggest that exchange between biogeographic regions across the Old World Savannah Biome were favoured in the Late Miocene, but became increasingly latitudinally fragmented from the Pliocene onwards. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Direct studies of recent epeiric seawater chemistry and their geological significance are relatively few compared to the far more abundant studies from ancient epeiric marine carbonates. Acknowledging the limitations of analogue studies in the modern glaciated world, we propose that the recent Abu Dhabi offshore and lagoonal areas share important attributes with the shallow-marine coastal zones of a subtropical epeiric carbonate sea. The study area in Abu Dhabi is dwarfed by the vast epeiric seas of the geological past, but its seawater properties and related geochemistry have relevance for paleoenvironmental interpretations for similar ancient systems. This study documents the geochemical properties of seawater along the Abu Dhabi coast, and discusses their trends within a spatial context. Results show a positive correlation between salinity, temperature, elemental concentrations, and oxygen isotopic composition of seawater, indicating a significant influence of evaporation on seawater chemistry. A distal-to-proximal negative correlation between seawater Mg/Ca and Sr/Ca ratios may be related to a landward increase in abundance of high-Mg calcite foraminifera. After normalization to chloride, seawater elemental (Ca2+, Mg2+, Sr2+) concentrations and alkalinity show decreasing trends in a landward direction, consistent with seawater aging from the open marine to restricted lagoonal settings. Lower ΔAlk (alkalinity change) : ΔCa2+ (Ca2+ change) ratios in seawater compared with the theoretical value, and more negative δ13CDIC values relative to typical (sub)tropical oceans in the study area indicate an influence of factors apart from CaCO3 precipitation on properties of aged seawater. An input of alkalinity and 12C-enriched carbon by organic carbon decomposition (via sulfate reduction) during early diagenesis is proposed to account for these deviations from typical values. The input of alkalinity and 12C-enriched carbon by organic carbon decomposition may be further related to reduced seawater pCO2 and early-marine cementation. Findings discussed here suggest that organic carbon decomposition during early-marine diagenesis may influence the geochemical properties of the coastal areas of shallow epeiric seas, and thus assumedly produce significant differences in proxy data compared with those from carbonates deposited in open oceans.

During glacial terminations, massive iceberg discharges and meltwater pulses in the North Atlantic triggered a shutdown of the Atlantic Meridional Overturning Circulation (AMOC). Speleothem calcium carbonate oxygen isotope records (δ18OCc) indicate that the collapse of the AMOC caused dramatic changes in the distribution and variability of the East Asian and Indian monsoon rainfall. However, the mechanisms linking changes in the intensity of the AMOC and Asian monsoon δ18OCc are not fully understood. Part of the challenge arises from the fact that speleothem δ18OCc depends on not only the δ18O of precipitation but also temperature and kinetic isotope effects. Here we quantitatively deconvolve these parameters affecting δ18OCc by applying three geochemical techniques in speleothems covering the penultimate glacial termination. Our data suggest that the weakening of the AMOC during meltwater pulse 2A caused substantial cooling in East Asia and a shortening of the summer monsoon season, whereas the collapse of the AMOC during meltwater pulse 2B (133,000 years ago) also caused a dramatic decrease in the intensity of the Indian summer monsoon. These results reveal that the different modes of the AMOC produced distinct impacts on the monsoon system., Nature Geoscience, 14 (12), ISSN:1752-0908, ISSN:1752-0894

The global development and modern distribution of arid zones in subtropical regions (drylands) are likely associated with the global cooling marking the dawn of the Quaternary (~2.6 Ma). This coincides with global shifts in ocean circulation patterns, the intensification of the Walker-Hadley circulation, declining atmospheric CO2, the initiation of glacial–interglacial cycles and the intensification of Northern Hemisphere glaciation, the combination of which has led to the current global distribution of non-polar deserts at ~30° latitude. Although modern drylands represent Earth’s largest terrestrial biome, covering ~46% of global land surfaces and supporting a global population of ~3 billion people, it is currently unclear how drylands will change under future climate change scenarios. Speleothems, preserved in arid-zone caves, are particularly useful terrestrial climate archives as they act as underground rain gauges, which require a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Here, we present new data from speleothems during past ‘warm periods’ from the Arabian hyper-arid zone. We apply a novel technique of extracting speleothem fluid inclusions waters to reconstruct the isotopic composition (d18O and d2H) of ‘fossil rainwater’ preserved in the speleothem fabric pristinely over millions of years. Speleothem evidence suggests that during the last 7 million years, the Sahara-Arabian desert experienced numerous intermittent humid phases, typically occurring with periods of low global ice-volume and warmer global temperatures. We further explore tropical push-pull mechanisms driving heating of the deep tropics and subsequent expansion of the tropical zone and synchronicity of humid phases regionally. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Methods for reconstructing past temperatures from speleothems have only recently been developed. Advances in quantitative temperature proxies for speleothems are now allowing critical knowledge gaps to be filled, given the outstanding age control and wide geographical distribution of the speleothem archive. The methods of reconstructing temperatures from speleothems are diverse: they rely on concepts from geochemistry, biology, and physics, and are based on different aspects of speleothems, including water inclusions, calcite, and organic molecules. Combining the different approaches makes temperature reconstructions more robust, affords further insights into the methodologies, and provides constraints on other climate variables.

A speleothem fluid inclusion extraction and isotope analysis system was established based on a vacuum extraction device and a Picarro L2140-i wavelength scanned cavity ring-down spectroscopy (WS-CRDS) water isotope analyzer. WS-CRDS allows to measure the stable oxygen and hydrogen isotope composition ( δ 18O and δ D) of small water samples simultaneously, which is faster, simpler, and requires less maintenance compared to currently used continuous-flow isotope ratio mass spectrometry (CF-IRMS). The precision of water isotopic analysis utilizing the WS-CRDS is often superior to that of CF-IRMS. Therefore, the use of Picarro for isotope analysis has rapidly gained popularity. The oxygen isotopic composition of speleothem calcite ( δ 18Oc) is one of the main proxies of speleothem-based paleoclimate reconstructions, but the interpretation of δ 18Oc remains complex as it can be influenced by many factors. Speleothem fluid inclusions contain the characteristics of cave drip water. The δ 18O and δ D values of fluid inclusion water provide direct information about paleoprecipitation, and can be further used to reconstruct paleotemperature when combined with δ 18Oc. The present paper contains a detailed description of the system as we have designed it, and provides an introduction to the system’s performance. The vacuum extraction device, connected to the Picarro analyzer, is designed to release the water trapped in speleothem fluid inclusions by pneumatically-operated crushing of discrete speleothem calcite chips. The whole device is kept at a temperature of 120°C to ensure the total and instantaneous vaporization of the water without isotopic fractionation. The vaporized water is carried by a flow of high-purity nitrogen to a 40 mL volume for homogenization, and is then introduced into the Picarro analyzer for δ 18O and δ D analysis. A syringe injection unit was added to the vacuum extraction device to be able to measure standard water, with δ 18O and δ D values similar to the speleothem samples, before and during measurements. To verify the precision and accuracy of the system, the same standard water samples were measured with an automated Picarro L2140-i set-up that includes an autosampler and a Picarro evaporation unit. The δ 18O and δ D values of standard waters as measured by both systems are comparable. Using the crushing device, speleothem samples from the East Asian Monsoon region yield paired δ 18O/ δ D values within ±0.5‰ of the Global Meteoric Water Line (GMWL), indicating no isotopic fractionation during the measurements. The precision is a function of the water amount released and of the isotopic composition of the sample. The reproducibility of crushed speleothem samples, whose water vapor concentration is between 2500 and 50000 ppm, is 0.5‰ for δ 18O and 2‰ for δ D (1 SD), similar to results obtained from other published measuring systems.

Historical coral skeleton (CS) δ18 O and δ15 N records were produced from samples recovered from sedimentary deposits, held in natural history museum collections, and cored into modern coral heads. These records were used to assess the influence of global warming and regional eutrophication, respectively, on the decline of coastal coral communities following the development of the Pearl River Delta (PRD) megacity, China. We find that, until 2007, ocean warming was not a major threat to coral communities in the Pearl River estuary; instead, nitrogen (N) inputs dominated impacts. The high but stable CS-δ15 N values (9‰-12‰ vs. air) observed from the mid-Holocene until 1980 indicate that soil and stream denitrification reduced and modulated the hydrologic inputs of N, blunting the rise in coastal N sources during the early phase of the Pearl River estuary urbanization. However, an unprecedented CS-δ15 N peak was observed from 1987 to 1993 (>13‰ vs. air), concomitant to an increase of NH4+ concentration, consistent with the rapid Pearl River estuary urbanization as the main cause for this eutrophication event. We suggest that widespread discharge of domestic sewage entered directly into the estuary, preventing removal by natural denitrification hotspots. We argue that this event caused the dramatic decline of the Pearl River estuary coral communities reported from 1980 to 2000. Subsequently, the coral record shows that the implementation of improved wastewater management policies succeeded in bringing down both CS-δ15 N and NH4+ concentrations in the early 2000s. This study points to the potential importance of eutrophication over ocean warming in coral decline along urbanized coastlines and in particular in the vicinity of megacities.

Made available in DSpace on 2022-04-28T17:20:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-06-03 Max Planck Research Group Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Wilhelm and Else Heraeus Foundation Deutsche Forschungsgemeinschaft Earth's climatic evolution over the last 5 million years is primarily understood from the perspective of marine mechanisms, however, the role of terrestrial feedbacks remains largely unexplored. Here we reconstruct the last 5 million years of soil moisture variability in Central Asia using paleomagnetism data and isotope geochemistry of an 80 m-thick sedimentary succession at Charyn Canyon, Kazakhstan. We identify a long-term trend of increasing aridification throughout the period, along with shorter-term variability related to the interaction between mid-latitude westerlies and the Siberian high-pressure system. This record highlights the long-term contribution of mid-latitude Eurasian terrestrial systems to the modulation of moisture transfer into the Northern Hemisphere oceans and back onto land via westerly air flow. The response of Earth-surface dynamics to Plio-Pleistocene climatic change in Central Asia likely generated terrestrial feedbacks affecting ocean and atmospheric circulation. This missing terrestrial link elucidates the significance of land-water feedbacks for long-term global climate. Late Cenozoic variation in Central Asian hydroclimate resulted from the interaction between mid-latitude westerlies and the Siberian high-pressure system and may have driven terrestrial feedbacks, according to analyses of sediments from Charyn Canyon, Kazakhstan. Max Planck Inst Chem, Res Grp Terr Palaeoclimates, Mainz, Germany Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, Rio Claro, Brazil Max Planck Inst Chem, Climate Geochem, Mainz, Germany Univ Paris, Inst Phys Globe Paris, Paris, France Aix Marseille Univ, CNRS, IRD, INRAE,Coll France,CEREGE, Aix En Provence, France Inst Geol Sci K Satpaeva, Alma Ata, Kazakhstan Goethe Univ Frankfurt, Inst Geosci, Frankfurt, Germany Goethe Univ Frankfurt, Frankfurt Element & Isotope Res Ctr, Frankfurt, Germany Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, Rio Claro, Brazil CNPq: 424365/2016-2 Deutsche Forschungsgemeinschaft: INST 161/921-1 FUGG

Nitrogen isotoperatios (δ15N) are a well-established tool for investigating the dietary and trophic behavior of animals in terrestrial and marine food webs. To date, δ15N values in fossils have primarily been measured in collagen extracted from bone or dentin, which is susceptible to degradation and rarely preserved in deep time (>100,000 years). In contrast,tooth enamelorganic matter is protected from diagenetic alteration by the mineral structure of hydroxyapatite and thus is often preserved overgeological time. However, due to the low nitrogen content (isotopic compositionhas been prevented by the analytical limitations of traditional methods. Here, we present a novel application of the oxidation-denitrification method that allows measurement of δ15N values in tooth enamel (δ15Nenamel). This method involves the oxidation of nitrogen in enamel-bound organic matter to nitrate followed by bacterial conversion of nitrate to N2O, and requires ≥100 times less nitrogen than traditional approaches. To demonstrate that δ15Nenamelvalues record diet and trophic behavior, we conducted a controlled feeding experiment with rats and guinea pigs (n=37). We determined that nitrogen concentration in tooth enamel (x̄=5.0±1.0 nmol/mg) is sufficient for δ15Nenamelanalyses with ≥5 mg untreated enamel powder. The nitrogen isotope composition of enamel reflects diet with an enrichment (Δ15Nenamel-diet) of ca. 2–4‰. δ15Nenamelvalues differ significantly between dietary groups and clearly record a shift from pre-experimental to experimental diet. The small sample size required (≤5 mg) by this method permits analyses of sample size-limited, diagenetically robust tooth enamel, and, as such it represents a promising new dietary proxy for reconstructing food webs and investigating thetrophic ecologyof extant and extinct taxa.

We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that covers the interval between 46.2 to 15.3 ka before present on millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The dataset can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where the first cluster comprises samples from cold and dry periods, such as Heinrich and Greenland stadials, as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials, but also for some from Heinrich Stadial 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation is found negligible. Consequently, variations of last glacial hydro-climate and temperature in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of c. 3 °C during the LGM compared to modern cave temperature. During Heinrich Stadials 2 and 3, reconstructed cave temperatures yield an additional cooling of 2.9 ± 2.6 °C and 4.4 ± 0.6 °C, respectively. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during interstadial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable or only slightly weaker than today.

Tectonic forces generated during thrust emplacement along active margins may drive complex fluid-flow patterns in fold-thrust belts and foreland basins. Isotope data (d2Hand d18O) of fluid inclusions hosted in calcite vein cements are used to reconstruct regional fluid migration pathways in the Albanide fold-thrust system. The calcite veins used in this study developed in a sequence of naturally fractured Cretaceous-Eocene carbonate rocks as a result of episodic throughput of fluids fromthe early stages of burial onward. The acquired fluid inclusion isotope data demonstrate that fluids circulating in the carbonates were derived from an underlying reservoir that consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin and ascended as soon as fracturing induced a sufficient increase in permeability. Structural and petrographic observations provide time constraints for the various phases of fracture infilling and reveal an increasing dominance of meteoric water in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out. Similar fluid-flow evolutions have previously been recorded in various fold-thrust belt settings elsewhere in the world.

Trinil (Java, Indonesia) yielded the type fossils of Homo erectus and the world?s oldest hominin-made engraving. As such, the site is of iconic relevance for paleoanthropology. However, our understanding of its larger geological context is unsatisfactory. Previous sedimentological studies are around 100 years old and their interpretations sometimes contradictory. Moreover, the existing stratigraphic framework is based on regional correlations, which obscure differences in local depositional dynamics. Therefore, a new and more local framework is urgently needed. We carried out a comprehensive geological study of the Trinil area. Using a Digital Elevation Model, we identified seven fluvial terraces. Terrace deposits were described and OSL-dated and fluvial behaviour was reconstructed. The terraces were correlated with terraces of the Kendeng Hills (e.g. the hominin-bearing Ngandong terrace) and date back to the past -350 ka. Thus far, most of the Trinil terraces and their deposits had remained unidentified, confounding sedimentological and stratigraphic interpretations. The exposed pre-terrace series has a thickness of -230 m. Together with the terraces, it forms a -3 Ma record of tectonism, volcanism, climate change and sea-level fluctuations. We subdivided the series into five new and/or revised stratigraphic units, representing different depositional environments: Kalibeng Formation, Padas Malang Formation, Batu Gajah Formation, Trinil Formation and Solo Formation. Special attention was paid to erosional contacts and weathering profiles, forming hiatuses in the depositional series, and offering insight into paleoclimate and base-level change. The Trinil Formation provides a new landscape context of Homo erectus. Between -550 and 350 ka, the area was part of a lake basin (Ngawi Lake Basin), separated from the marine base level by a volcanic barrier, under dry, seasonal conditions and a regular supply of volcanic ash. An expanding and retreating lake provided favourable living conditions for hominin populations. After 350 ka, this role was taken over by the perennial Solo River. Landscape reconstructions suggest that the Solo formed by headward erosion and stream piracy, re-connecting the Ngawi Lake Basin to the plains in the west. Our study offers a local framework, but its Pleistocene landscape record has regional significance. Most of all, it forms a much-needed basis for future, detailed studies on the build-up of the hominin site of Trinil, its fossil assemblages and numerical ages. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Rationale Since their introduction more than a decade ago, isotope ratio infrared spectroscopy (IRIS) systems have rapidly become the standard for oxygen (δ18O) and hydrogen (δ2H) isotope analysis of water samples. An important disadvantage of IRIS systems is the well-documented sample-to-sample memory effect, which requires each sample to be analyzed multiple times before the desired accuracy is reached, lengthening analysis times and driving up the costs of analyses. Methods We present an adapted set-up and calculation protocol for fully automated analysis of water samples using a Picarro L2140-i cavity ring-down spectroscopy instrument. The adaptation removes memory effects by use of a continuously moisturized nitrogen carrier gas. Water samples of 0.5 μL are measured on top of the water vapor background, after which isotope ratios are calculated by subtraction of the background from the sample peaks. Results With this new technique, single injections of water samples have internal precisions (1σ) below 0.05‰ for δ18O values and 0.1‰ for δ2H values, regardless of the isotope ratio of the previous sample. Precision is worse, however, when the isotope difference between the sample and background water is too large (i.e., exceeding approximately 9‰ for δ18O values and 70‰ for δ2H values). Isotope ratios show negligible drift across the four weeks within which the experiments were performed. The single-injection 1σ precision for 17O excess (Δ′17O) determined with this method is 60 per meg. Conclusions Our experiments demonstrate that by removing sample-to-sample memory effects with a moisturized carrier gas, the time for measurement of δ18O and δ2H values using an IRIS system can be reduced markedly without compromising the analytical precision and accuracy. Thorough replication is needed to achieve sufficiently low uncertainties for Δ′17O., Rapid Communications in Mass Spectrometry, 35 (8), ISSN:1097-0231, ISSN:0951-4198

Loess-Palaeosol Sequences (LPS) represent the most extensive Quaternary terrestrial archives. Although researchers have long been able to identify short-lived climatic changes in LPS through stratigraphy, until recently we have lacked the tools to 1) identify how continuous loess archives may be, and to what extent short-lived, millennial-timescale climatic events were recorded in loess sediments, and to 2) quantitatively reconstruct past climate parameters from loess proxies. Stratigraphically, the impact of short-lived climatic cycles can be observed in the form of primary loess deposits reflecting cold stadial conditions, intercalated with arctic and boreal brown soils and tundra gley horizons indicating milder interstadials. Short-term establishment and subsequent degradation of an active permafrost layer can also be identified in temperate-latitude loess such as that found in the Rhine Valley of central-western Europe. Recently developed proxy methods can now be used to quantify climatic parameters such as temperature and precipitation in these regions 1,2. Associated with radiocarbon dating, these new approaches will vastly improve our understanding of continental environmental changes through the Upper Pleistocene, which can now be compared at high temporal resolution with marine and ice core records. In particular, the quantity and stable isotope ratios of crystalline calcite granules (> 0.8 mm), secreted by earthworms (Lumbricus sp.) at the soil surface, preserve climate information contemporaneous with deposition of the loess sediment.In this study, we assess the utility of the earthworm calcite granules (ECG) approach by reconstructing temperature and precipitation at high resolution between 50 and 15 ka from two temporally overlapping loess sequences, Schwalbenberg and Nussloch, situated approximately 200 km apart in the German Rhine Valley. ECG counts down the two profiles reveal millennial-timescale climatic variations; high ECG concentrations associated with pedogenetic horizons suggest milder climatic with increasing biological activity and vegetation cover. Using empirical equations based on 1) observations of modern earthworm response to temperature and 2) the linear relationship between ∆13C values of plants and precipitation, the stable oxygen and carbon isotope compositions from ECGs can be used as direct proxies for warm season temperature and annual soil moisture, respectively. We embed our climate reconstructions within Bayesian age models based on radiocarbon dating of ECG in order to establish precise correlations between the two sequences and with other climatic archives. We find that ECGs provide valuable proxies able to meaningfully quantify palaeoclimate variations from terrestrial deposits over millennial timescales. Our results further show periods of quasi-simultaneous climatic change in the Northern Hemisphere, closely linking the climatic signatures recorded in the Upper Pleistocene of Schwalbenberg and Nussloch to the Greenland ice core records.References: 1. Prud’homme, C. et al. Palaeotemperature reconstruction during the Last Glacial from δ18O of earthworm calcite granules from Nussloch loess sequence, Germany. Earth Planet. Sci. Lett. 442, 13–20 (2016).2. Prud’homme, C. et al. δ 13C signal of earthworm calcite granules: a new proxy for palaeoprecipitation reconstructions during the Last Glacial in Western Europe. Quat. Sci. Rev. 179, 158–166 (2018).

Human activities within the context of a drying trend triggered the megafaunal extinctions in Madagascar and Mascarene Islands., Madagascar and the Mascarene Islands of Mauritius and Rodrigues underwent catastrophic ecological and landscape transformations, which virtually eliminated their entire endemic vertebrate megafauna during the past millennium. These ecosystem changes have been alternately attributed to either human activities, climate change, or both, but parsing their relative importance, particularly in the case of Madagascar, has proven difficult. Here, we present a multimillennial (approximately the past 8000 years) reconstruction of the southwest Indian Ocean hydroclimate variability using speleothems from the island of Rodrigues, located ∼1600 km east of Madagascar. The record shows a recurring pattern of hydroclimate variability characterized by submillennial-scale drying trends, which were punctuated by decadal-to-multidecadal megadroughts, including during the late Holocene. Our data imply that the megafauna of the Mascarenes and Madagascar were resilient, enduring repeated past episodes of severe climate stress, but collapsed when a major increase in human activity occurred in the context of a prominent drying trend.

© 2020 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd Rationale: Oxygen (δ18O) and carbon (δ13C) isotope analysis of foraminifera and other CaCO3 samples has been a key technique for paleoceanographical and paleoclimatological research for more than 60 years. There is ongoing demand for the analysis of ever smaller CaCO3 samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel. Methods: We present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample CO2 to analyse CaCO3 samples in a weight range between 10 and 3 μg. These are considerably lower sample weights than achievable on most currently available standard instrumentation. The technique is automated, so that sample throughput lies at >60 samples per day. The method involves an on-line vial-flushing routine designed to remove machine drift due to blank CO2 build-up in the sample vials. Results: In a series of experiments the effect of blank CO2 build-up is quantified, and outgassing from the chlorobutyl septa identified as the source. An improved flushing routine together with the use of a cryo-focusing step in the analysis is demonstrated to provide the analytical stability and sensitivity to analyse CaCO3 samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ18O and δ13C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples. Conclusions: This study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO3 samples smaller than 5 μg by use of a continuous-flow isotope technique. Of key importance are (1) the application of a cold trap that drastically reduces sample gas loss, and (2) a modified flushing regime that eliminates increasing background CO2 build-up in sample vials during longer automated sample runs., Rapid Communications in Mass Spectrometry, 34 (19), ISSN:1097-0231, ISSN:0951-4198

Rationale Online oxygen (δ18O) and hydrogen (δ2H) isotope analysis of fluid inclusion water entrapped in minerals is widely applied in paleo‐fluid studies. In the state of the art of fluid inclusion isotope research, however, there is a scarcity of reported inter‐technique comparisons to account for possible analytical offsets. Along with improving analytical precisions and sample size limitations, interlaboratory comparisons can lead to a more robust application of fluid inclusion isotope records. Methods Mineral samples—including speleothem, travertine, and vein material—were analyzed on two newly setup systems for fluid inclusion isotope analysis to provide an inter‐platform comparison. One setup uses a crusher unit connected online to a continuous‐flow pyrolysis furnace and an isotope ratio mass spectrometry (IRMS) instrument. In the other setup, a crusher unit is lined up with a cavity ring‐down spectroscopy (CRDS) system, and water samples are analyzed on a continuous standard water background to achieve precisions on water injections better than 0.1‰ for δ18O values and 0.4‰ for δ2H values for amounts down to 0.2 μL. Results Fluid inclusion isotope analyses on the IRMS setup have an average 1σ reproducibility of 0.4‰ and 2.0‰ for δ18O and δ2H values, respectively. The CRDS setup has a better 1σ reproducibility (0.3‰ for δ18O values and 1.1‰ for δ2H values) and also a more rapid sample throughput (, Rapid Communications in Mass Spectrometry, 34 (16), ISSN:1097-0231, ISSN:0951-4198

Oxygen (δWe present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample COIn a series of experiments the effect of blank COThis study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO

Vein-hosted fluid inclusions may represent remnants of subsurface paleo-fluids and therefore provide a valuable record of fracture-controlled fluid flow. Isotope data (δ2H and δ18O) of fluid inclusions are particularly useful for studying the provenance and type of paleo-fluids circulating in the subsurface. Although isotopic analysis of sub-microliter amounts of fluid inclusion water is not straightforward, major steps forward have been made over the past decade through the development of continuous-flow set-ups. These techniques make use of mechanical crushing at a relatively low-temperature (110˚C) and allow for on-line analysis of both δ2H and δ18O ratios of bulk fluid inclusion water. However, continuous-flow techniques have mostly been used in speleothem research, and have not yet found a widespread application on vein systems for hydrogeological reconstructions.We used isotope data of fluid inclusions hosted in calcite vein cements to reconstruct regional fluid migration pathways in the Albanian foreland fold-and-thrust system. Tectonic forces during thrust emplacement typically instigate distinct phases of fracturing accompanied by complex fluid flow patterns. The studied calcite veins developed in a sequence of naturally fractured Cretaceous to Eocene carbonate rocks as a result of several fracturing events from the early stages of burial onward. Fluid inclusion isotope data of the veins reveal that fluids circulating in the carbonates were derived from an underlying reservoir, which consisted of a mixture of meteoric water and evolved marine fluids, probably derived from deep-seated evaporites. The meteoric fluids infiltrated in the hinterland before being driven outward into the foreland basin. The fluid inclusion isotope data furthermore show that meteoric water becomes increasingly dominant in the system through time as migration pathways shortened and marine formation fluids were progressively flushed out.The diagenetic stability of fluid inclusions is of key interest in the study of their isotope ratios. Recrystallization, secondary fluid infiltration and isotope exchange processes could potentially drive alterations of fluid inclusion isotope signatures after entrapment. In this case, however, isotope signatures of fluid inclusions seem to have remained largely unaltered, despite the Cretaceous to Tertiary age of the vein system. Oxygen isotope exchange processes between the fluid inclusion water and host mineral could have been inhibited at the relatively low temperatures of vein formation (i.e.

One of the most commonly used methods for dating carbonate deposits, such as speleothems or calcareous sinter deposits, is the 230Th/U-disequilibrium method. With this approach, ages up to 500 ka can be obtained. However, especially for late Holocene samples, substantial detrital contamination may represent a major problem for radiometric dating. The high 232Th content, which is an indicator for the amount of detrital contamination, leads to elevated U/Th-ages and generally larger uncertainties, which limit the potential of the corresponding samples for paleoclimate reconstructions. Ingrowth 226Ra shows the potential to be used as an alternative dating method. In combination with Ba, U and Th, it is possible to date samples with ages up to 8 ka.In general, there are three sources of 226Ra in carbonate samples. (i) excess 226Ra incorporated during deposition of the material, (ii) detrital material present in the carbonate, and (iii) ingrowth 226Ra produced by the radioactive decay of its parent 230Th. Due to the geochemically similar behavior of Ra and Ba, it is possible to correct for the amount of excess 226Ra. As for the 230Th/U-disequilibrium method, 232Th can be used to correct for detrital contamination.To test our new method, we applied it to several calcareous sinter samples from different Roman aqueducts, which supplied drinking water to ancient cities such as Jerash or Cordoba . The separation of Ra, Ba, U and Th from the matrix of the samples is performed using a single aliquot of material and different ion exchange resins. Prior to the separation process, a calibrated mixed Ra-Ba-Th-U spike solution was added and equilibrated with the sample solution. The results are not only compared to model simulations for the new system, but also to ages obtained with the conventional 230Th/U-method.

Mainland Southeast Asia is located on the moisture transport route of the Indian summer monsoon (ISM) where hydroclimate records from speleothems have rarely been investigated. Here, we present a new multi-proxy (δ18O and δ13C values, trace element concentrations, and grayscale values) data set of stalagmite KPC1 from Khao Prae cave in western Thailand spanning the last 1400 years (500–1900 CE; the Common Era). These multi-proxy data reveal a high variability between the wet and dry periods during 500–850 CE and 1150–1300 CE, stable climate conditions during 850–1150 CE, and overall dry conditions since 1300 CE. The δ13C values, trace elements concentrations, and grayscale values show centennial-scale fluctuations, which were probably driven by local hydrological processes. In contrast, variations in the stalagmite δ18O values reflect integrated changes in rainfall amount from the ISM. The KPC1 record agrees with other speleothem δ18O records of Southeast Asian summer monsoon from the last millennium, as well as the lake multi-proxy and tree-ring PDSI data from Mainland Southeast Asia, but diverges from records from the Indo-Pacific equatorial regions and the western Pacific. We conclude that hydroclimate variability at the western side of Mainland Southeast Asia is mainly driven by changes in moisture transport of the ISM. On socially relevant timescales, the KPC1 data set shows that a period of stable rainfall (850–1150 CE) coincides with the early success of the early empires (e.g., Pagan, Angkor, and Dai Viet) in Mainland Southeast Asia. In line with previous studies in the region, we speculate that the high variability in rainfall between 1150 and 1300 CE and droughts during 1300–1550 CE played a significant role in the demise of ancient societies in Southeast Asia. National Research Foundation (NRF) Accepted version S. Chawchai wishes to express appreciation for the financial support provided by the Development and Promotion of Science Technology (DPST) Research grant 042/2558 and DAAD faculty research grant 2016. X. Wang is supported by Singapore National Research Foundation grants (2017NRF-NSFC001-047 and NRFF2011-08). D. Scholz is thankful to the German Research Foundation (DFG SCHO 1274/9-1 and SCHO 1274/11-1). The authors also thank Dr. S. Tonongto, his family and PANDA CAMP for accommodation and assistance during the field survey, and Prof. M. Choowong as a mentorship for SC. In addition, the authors thank officials at Ban Rai district, Uthai Thani province for their help and hospitality. We also thank S. Mischel for his help with TERMITE and A. Budsky for cutting the sample for LA-ICP-MS analysis, W. Suwansukho and P. Rattanasrimongkol for polishing the samples and discussion, and the Research Clinic Unit, Office of Research Affairs at Chulalongkorn University for assistance during manuscript preparation.

The intra-mountainous Saar-Nahe Basin (SNB), SW Germany, a strike-slip-fault basin formed during the Variscian orogeny, was filled by a large freshwater lake system during the Early Permian. The SNB experienced intense syn- and post-depositional magmatic activity, resulting in a complex volcano-sedimentary sequence of magmatic intrusions, lava flows and tephra deposits intercalating in continental red beds and limno-fluvial sediments. Fossils preserved in white color are found in Permo-Carboniferous fluvio-lacustrine siliciclastic floodplain sediments with thin intercalated limestone banks, of the Remigiusberg Formation in the SNB. The oldest amniote fossil of Germany and other partly articulated tetrapod remains were recovered from it at the Remigiusberg quarry near Kusel (e.g., Fröbisch et al., 2011; Voigt et al. 2014). These terrestrial tetrapods were discovered together with aquatic vertebrate fossils in close proximity (< 5 m; within the contact aureole) to an underlying decameter thick sill of kuselite, an auto-hydrothermally altered andesite. We aim to assess the thermal and chemical impact of post-depositional contact metamorphism and hydrothermal activity associated with this sill on the bioapatite of vertebrate skeletal remains by characterizing the elemental, isotopic and mineralogical composition of these fossils. White-colored, likely hydrothermally altered teeth of the freshwater shark Lebachacanthus were analyzed and compared to shark teeth of the same species retaining their original black color, from contemporaneous unmetamorphosed lacustrine black shale deposits in the SNB. In situ Electron Microprobe analysis and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) elemental profiles reveal distinct diagenetic histories for the black- and white-colored shark teeth. This is further supported by apatite ẟ18O and ẟ13C values, which indicate different secondary alteration by fluids for both facies. Raman spectroscopy and X-ray diffraction on bulk powder samples identify fluorapatite as the major mineral phase in all teeth. Apatite crystallinity of both dentin and enameloid is higher in white- than in black-colored fossils, consistent with crystallite growth due to thermal overprint of > 500 °C. For both, white- and black-colored shark teeth, LA-ICP-MS U-Pb analyses yield inconclusive data and unexpectedly young ages inconsistent with known ages of deposition or metamorphism. We are currently analyzing the petrology of the kuselite to constrain the metamorphic evolution of sediments in the contact aureole by modelling. Additionally, heating experiments of modern bioapatite samples are performed to further constrain the alteration temperature. Altogether, these data will enhance our understanding of the particular thermometamorphic/hydrothermal conditions required to form white-colored, recrystallized vertebrate fossils in the context of the magmatic-metamorphic evolution of the SNB. ReferencesFRÖBISCH, J., SCHOCH, R.R., MÜLLER, J., SCHINDLER, T. & SCHWEISS, D.J. (2011): The oldest amniote from Germany: a sphenacodontid synapsid from the Saar-Nahe Basin. Acta Palaeontologica Polonica, 56: 113–120. VOIGT, S., FISCHER, J., SCHINDLER, T., WUTTKE, M., SPINDLER, F. & RINEHART, L. (2014): On a potential fossil hotspot for Pennsylvanian-Permian nonaquatic vertebrates in Europe. Freiberger Forschungshefte, C548: 39–44.

In the context of human evolution and dispersal in Africa, it is important to understand past climate conditions and changes as possible drivers of these processes. One of the most recent climatic events was the end of the African Humid Period (AHP) at around 5 ka BP. This was marked by a decrease in precipitation following a long wet-phase in northern and eastern Africa, which caused many lakes to decrease in size or even desiccate. Although the termination of the AHP is well known, the timing and rate of the transition from wet to dry conditions is still heavily debated. To investigate the termination of the AHP at a high temporal resolution (subdecadal and subannual), fossil stromatolites and Etheria elliptica shells from paleo-shorelines in the Chew Bahir Basin, southern Ethiopia, were collected. Today, Lake Chew Bahir is a deltaic swamp, however in past pluvials a large lake was present that likely overflowed and connected to other basins similar to other amplifier lakes in the East African Rift System. Radiocarbon dating, oxygen and carbon stable isotope analyses, trace element analyses and petrographic mapping of stromatolite laminae structure were conducted. A strong correlation between δ18O and δ13C shows that paleo-lake Chew Bahir likely experienced highly evaporative conditions and indicate an endorheic state of the basin in times of stromatolite growth at 7.1, 5.8, 4.7 and 4.6 ka BP. Furthermore, our findings suggest highly fluctuating environmental conditions during these times and demonstrate that the transition to drier conditions was not a strictly linear trend. In summary, the stromatolites and Etheria elliptica shells are an excellent environmental archive due to their high temporal resolution, precise dating (± 30 yrs) and an indication of the paleo-lake water depth. These types of records provide insights to past changes in freshwater availability, the variability of which would have had large consequences for humans living in the region.

Most paleoceanographic studies using planktic foraminifera focus on annual means, but seasonal signals buried by the analyses of lumped specimens could be very valuable. Surface ocean feedbacks on climate change may be more significant in the seasonal realm than annual mean in the northern South China Sea, a region being strongly affected by Asian monsoons and tropical cyclones. Here we use oxygen isotope measurements on individual specimens of surface and subsurface planktic foraminiferal species to reconstruct surface seasonality and seasonal upper ocean stratification in this region. Many studies have shown that the thermocline was deeper in the tropical Pacific during the Pliocene than the Pleistocene, but the mechanism remains unclear. Several processes could lead to changes in the upper ocean stratification, such as changes in sea surface temperature and upper ocean mixing by tropical cyclones. Our results show that the upper ocean stratification was weaker during the Late Pliocene than the Early Pleistocene, with the change more significant in summer than winter, while no systematic offset is observed in the surface seasonality. The observations suggest that enhanced mixing by tropical cyclones might be the major cause of the deeper thermocline during the Pliocene.

International audience; In the Amazon basin, intense precipitation recycling across the forest significantly modifies the isotopic composition of rainfall (δ18O, δD). In the tropical hydrologic cycle, such an effect can be identified through deuterium excess (dxs), yet it remains unclear what environmental factors control dxs, increasing the uncertainty of dxs‐based paleoclimate reconstructions. Here we present a 4‐year record of the isotopic composition of rainfall, monitored in the northwestern Amazon basin. We analyze the isotopic variations as a function of the air mass history, based on atmospheric back trajectory analyses, satellite observations of precipitation upstream, leaf area index, and simulated moisture recycling along the transport pathway. We show that the precipitation recycling in the forest exerts a significant control on the isotopic composition of precipitation in the northwestern Amazon basin, especially on dxs during the dry season (r = 0.71). Applying these observations to existing speleothem and pollen paleorecords, we conclude that winter precipitation increased after the mid‐Holocene, as the expansion of the forest allowed for more moisture recycling. Therefore, forest effects should be considered when interpreting paleorecords of past precipitation changes.

Hydrothermal fluid flow along fault zones in the Harz Mountains led to widespread formation of economic vein-type Pb–Zn ore and Ba–F deposits during the Mesozoic. We reconstruct the fluid flow system responsible for the formation of these deposits using isotope ratios (δ2H and δ18O) and anion and cation contents of fluid inclusions in ore and gangue minerals. Building forward on extensive studies in the 1980s and 1990s, our new geochemical data reveal that seawater evaporation brines, which most likely originated from Zechstein evaporites, descended deeply into Paleozoic rocks to leach metals at depth. In Jurassic times, these metal-rich brines episodically recharged along fault zones and mixed with shallow crustal H2S-bearing brines. Primarily in the Upper Harz Mountains, this mixing system led to the formation of economic Pb–Zn–Cu mineralization, which locally shows banded textures with alternations of sulfide minerals and quartz or carbonate (mostly calcite). In the Middle and Lower Harz Mountains, Zechstein-derived brines interacted with K- and F-bearing basement rocks and/or magmatic rocks to deposit fluorite mineralization upon ascent in the Upper Cretaceous. The proposed model of mineralizing fluids originating as (evaporated) seawater has been shown to hold for numerous basin-hosted base-metal sulfide and fluoride deposits elsewhere in Europe.

Stable isotope analysis of biogenic carbonates has remained one of the most important tools in paleoceanography since Emiliani (1955) first described the fluctuation of oxygen isotopes in planktic foraminifers over the Pleistocene. Many laboratories now possess equipment with the capability to analyse foraminifer specimens singularly, at least for larger planktic forms.Being able to run single specimens of planktic foraminifers is significant, because it yields entirely different information than when one would analyse multiple specimens from the same species. Planktic foraminifers have an average life span of about one month, so analysing single specimens, makes paleoceanographic data at seasonal resolution available (e.g. Ganssen et al., 2011; Metcalfe et al 2019, and references therein).Most modern equipment for stable isotope analysis of CaCO3 samples yields good precision down to 10 microgram sample size. The smallest samples are generally measured with a dual inlet technique, because that quantitatively collects the CO2 gas sample in a cold trap before analysis, leading to a more efficient use of the sample gas. Modern dual inlet equipment has a sample size limit somewhere between 10 and 6 microgram CaCO3 sample weight, and in that range usually operates at increased analytical uncertainty when compared to larger samples (e.g. Ganssen et al., 2011). Smaller samples are problematic, because at small amounts of sample gas, the dual inlet system is not able to maintain viscous flow conditions required for precise isotope analysis. To circumvent that barrier, one can use continuous-flow (CF) mass spectrometry because in CF systems the carrier gas ensures proper flow conditions even if there is (virtually) no sample gas produced. Doing so has previously allowed for the isotope analysis of CaCO3 samples in the 10 – 6 microgram range at an external precision (1SD) of ~0.12‰ for both δ18O and δ13C (e.g. Metcalfe et al 2019).To further improve the performance of CF mass spectrometry for small CaCO3 samples, we ran experiments on a Thermo GASBENCH system, equipped with a cold trap (cf. Fiebig et al 2005) and interfaced with a Delta-V mass spectrometer. The experiments consisted of replicate analysis of CaCO3 standards between 10 and 3 micrograms in weight, which is the weight range of many of the smaller specimens of planktic foraminifers.Several hardware modifications were implemented to improve system stability and remove observed effects of contribution of blank CO2 building up in the sample vials. With these modifications, external reproducibility of the set-up for carbonate standard aliquots between 10 and 4 microgram reached a precision of ~0.10 ‰ for both δ18O and δ13C (1SD). This is similar to precisions typically attained for routine analysis of much larger samples in standard operation on the same equipment, and demonstrates that precise stable isotope analysis of smaller single-specimen planktic foraminifers than we could achieve so far is within reach of CF mass spectrometry.References:Emiliani, C. 1955, DOI: 10.1086/626295Fiebig, J., et al. 2005, DOI: 10.1002/rcm.2060Ganssen, G.M., et al., 2011, DOI:10.5194/cp-7-1337-2011Metcalfe, B., et al., 2019, DOI: 10.1029/2018PA003475

A distinct shift in δ18O, δ13C and trace element contents of the Pere Noel (PN) stalagmite from southern Belgium revealed an abrupt climatic anomaly at 8.13 ± 0.03 ka BP (before present = before 1950 AD). This anomaly is characterized by a maximum drop in the δ18O (−1.4‰ compared the mean) between 8.13 and 8.10 ka BP (±0.03). This drop of δ18O coincides with a decrease in δ13C and trace element (Sr, Ba and Mg) concentrations suggesting drier conditions. Our precise chronology provides the timing of the outburst of proglacial lakes Agassiz and Ojibway that caused the δ18O, δ13C and trace elemental anomalies at 8.13–8.10 ± 0.03 ka BP, which corresponds to the 8.2-ka BP event. The PN stalagmite bears δ18O values in fluid inclusions that covary with the δ18O values in calcite, suggesting that the speleothem calcite δ18O primarily reflects variations in the rainfall δ18O. Comparison of the PN record with different marine and terrestrial archives during the 8.2-ka BP event shows a good agreement in timing and duration, suggesting that the PN speleothem can be regarded as a valuable proxy to better understand the 8.2-ka BP event.

A fundamental issue in the interpretation of speleothem calcite δ18Occ records is the correct partitioning of the effects of temperature and water δ18O variations. This study explores the paleo-environmental evolution of the Eastern Mediterranean Sea (EMS) region using Soreq Cave speleothems in the last 160 ka, a period covering glacial MIS6 to the present, through the independent determinations of temperatures via carbonate clumped isotopes (Δ47) and fluid inclusion δ18Ow, δDw and d-excess values of cave water entrapped in the speleothems. The observed general agreement between the trends in water δ18Ow composition directly measured from fluid inclusions and calculated from Δ47 temperatures and δ18Occ support the robustness of the data. Δ47 temperatures, derived using a revised thermometer calibration that includes recent modifications in 17O correction, vary from high values of 20–22 °C during interglacial periods to low values of 11–12 °C in cold glacial and stadial periods. Temperatures of 19–22 °C are observed during the time of deposition in the EMS of sapropel S5 in the last interglacial MIS5e period and sapropel S1 in the early Holocene, immediately following Terminations II and I, respectively. The Soreq Cave Δ47 temperatures generally agree with previously estimated EM sea surface temperatures, in support of the absence of a significant land-sea temperature gradient. Cave water δ18Ow values show large variations (from ∼-3 to −7.5‰), with high glacial and low interglacial values. These variations are largely explained by changes in Mediterranean Sea water composition due to glacial ice melting and freshwater input during sapropel periods, combined with the effect of rainfall amounts during interglacial periods. An analysis of relative timing shows that temperature rise precedes hydrological changes in the initial stages of Termination events. Fluid inclusion d-excess values show clear variations between values similar to the Global Meteoric Water Line during cold periods and values similar to the local Eastern Mediterranean Meteoric Water Line (EMMWL) in warm periods.

Lacustrine carbonate deposits with spherulitic facies are poorly understood, but are key to understanding the economically important “Pre-Salt” Mesozoic strata of the South Atlantic. A major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite-dominated deposits which are known in outcrop. Stratigraphy and petrography suggest one of the best analogue systems is found in the Carboniferous of Scotland: the East Kirkton Limestone. Here we propose a hydrogeochemical model that explains why the CaCO3, SiO2, Mg-Si-Al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock. Demonstrating links between igneous bedrock chemistry, lake and spring water chemistry and mineral precipitation, this model has implications for studies of lacustrine sediments in rift basins of all ages. Using empirical and theoretical approaches, we analyze the relationship between metal mobilization from sub-surface volcaniclastic rocks and the potential for precipitation of carbonate minerals, various Mg-bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting. This suite of minerals is most likely formed by in-gassing of CO2 to a carbon-limited alkaline spring water, consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater. We suggest that an analogous system to that at East Kirkton caused development of the ‘Pre-Salt’ spherulitic carbonate deposits.

Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Jandaíra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post-rift stage of the Potiguar rift (NE Brazil). The Jandaíra Formation in the present onshore domain experienced 1000 km2. The carbonates have a gentle, 0, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub-vertical veins, and sub-vertical as well as sub-horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Jandaíra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Jandaíra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400-500 m. Deformation was accommodated by a dense network of sub-vertical mode I and hybrid fractures associated with sub-vertical stylolites developed in a stress field characterised by a sub-horizontal σ1 and sub-vertical σ2. The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Açu sandstone underlying the Jandaíra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800-900 m entering a depth interval characterised by a sub-vertical σ1. At this stage, sub-horizontal stylolites developed liberating calcite which sealed the sub-vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre-existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures. Basin Research

Historical coral skeleton (CS) δ

The Caspian Sea is an evolutionary island whose rich and endemic fauna have evolved in partial isolation over the past two million years. Baseline studies of pre-20th Century communities are needed in order to assess the severity of the current Caspian biodiversity crisis, which mostly involves invasive species. An inventory of late Holocene shelly assemblages (c. 2000–2500 cal yr BP) from outcrops in and around Great Turali Lake (Dagestan, Russia) shows a diverse nearshore community consisting of 24 endemic Caspian species, two invasive species and two Caspian native species that lived in a shallow embayment with mesohaline salinities of circa 5–13 psu (parts per thousands). This pre-crisis Holocene Caspian mollusc community serves as a baseline against which modern mollusc diversity measurements can be evaluated. Examination of faunas from similar environments living today and in the past illustrates the dramatic changes in nearshore communities during the 20th Century. Our study identifies a habitat that may have served as a refuge, but that is currently under threat from invasive species. The severity of the Caspian biodiversity crisis is comparable with other well-known biodiversity crises in semi-isolated ecosystems such as the cichlid fish communities of Lake Victoria, Africa.

The origin of spherical-radial calcite bodies - spherulites - in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The first is that spherulites precipitate from solutions super-saturated with respect to magnesium-silicate clays, such as stevensite. The second is that spherulite precipitation happens in the presence of dissolved, organic acid molecules. In both cases, experiments were performed under sterile conditions using large batches of a synthetic and cell-free solution replicating waters found in hyperalkaline, saline lakes (such as Mono Lake, California). Our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to calcite (control solution) will precipitate euhedral to subhedral rhombic and trigonal bladed calcite crystals. The same solution supersaturated with respect to stevensite precipitates sheet-like stevensite crystals rather than a gel, and calcite precipitation is reduced by ~. 50% compared to the control solution, producing a mixture of patchy prismatic subhedral to euhedral, and minor needle-like, calcite crystals. Enhanced magnesium concentration in solution is the likely the cause of decreased volumes of calcite precipitation, as this raised equilibrium ion activity ratio in the solution. On the other hand, when alginic acid was present then the result was widespread development of micron-size calcium carbonate spherulite bodies. With further growth time, but falling supersaturation, these spherules fused into botryoidal-topped crusts made of micron-size fibro-radial calcite crystals. We conclude that the simplest tested mechanism to deposit significant spherical-radial calcite bodies is to begin with a strongly supersaturated solution that contains specific but environmentally-common organic acids. Furthermore, we found that this morphology is not a universal consequence of having organic acids dissolved in the solution, but rather spherulite development requires specific binding behaviour. Finally, we found that the location of calcite precipitation was altered from the air:water interface to the surface of the glassware when organic acids were present, implying that attached calcite precipitates reflect precipitation via metal-organic intermediaries, rather than direct forcing via gas exchange.

This study focuses on the palaeoclimatic evolution and relative sea-level fluctuations of the northern branch of NeoTethys during the late Campanian–early Danian. The studied succession (Ismailler Section) is located in the Mudurnu–Goynuk Basin, NW Turkey and dominated by apparently continuous pelagic muddy deposits. Stable isotopic and elemental compositions of the mudrocks are investigated in order to evaluate the palaeoceanographic conditions as well as broad tectonic reconstruction of the basin. The mudrock geochemistry suggests a tectonic reorganization during late Campanian as reflected by a distinct shift from felsic to mafic sediment provenance. In the Ismailler Section, five δ13C events are identified; four or which are well correlatable with major events in other records around the world, such as the late Campanian Event (LCE), Campanian–Maastrictian Boundary (CMB) and the late Maastrichtian Event (LME). The relative sea-level variations in the basin typically match both short- and long-term global sea-level fluctuations. The remaining globally uncorrelatable δ13C event does coincide with tectonic uplift and the abrupt negative δ13C shift, and is inferred to be the result of regional factors. The dominance of worldwide events in the records of the relatively restricted ocean branch reflects the strength of global factors.

Climate changes close to the Lochkovian-Pragian Event are still widely discussed. Carbonate δ18O and δ13C and conodont apatite δ18O from medial to distal carbonate ramp sediments were analysed to provide further stable isotope data from the stratotype area in the Prague Basin. The uppermost Silurian to lower Emsian δ18O trends are put into an updated conodont biostratigraphy framework. Carbonate δ18O and δ13C are discussed in the context of facies-dependent diagenesis. The δ13C pattern measured from different sections enables the correlation of intervals with development of different facies inside the Prague Basin. Positive δ13C shifts are often coupled with trends of decreasing computed gamma-ray (CGR) values interpreted as regressions, whereas negative δ13C shifts commonly coincide with opposite trends in CGR. The Lochkovian-Pragian boundary interval coincided with an increase in carbonate δ13C and an increase in the δ18O of conodont apatite and carbonate, which we interpret as consequence of climate cooling. Generally, the Lochkovian was warmer than the Pragian and earliest Emsian.

Inoceramid prisms are among the most common microfossils that can be found in Late Cretaceous strata. Since these biomineral units were formed by sequential accretion in the outer shell layer of the bivalves, they potentially serve as archives of short-term (circa-annual) paleowater temperature fluctuations. In the present study, we tested to what extent intra-prismatic stable isotope variations of individual inoceramid prisms reflect sub-annual δ13C and the δ18O patterns. We obtained multiple carbonate samples from prisms recovered from the sediment and from a cross-sectioned inoceramid shell fragment and compared data from these samples to data from classical sclerochronological sampling (i.e., sequential drilling). The analyzed shell material belonged to the species Platyceramus platinus from the Smoky Hill Chalk Member (Niobrara Formation, Kansas, USA). Scanning electron microscopy (SEM) was used to evaluate the diagenetic alteration of the studied prisms and allowed to identify suitable material for stable isotope analyses. The δ18O values of drilled carbonate samples (δ18ODrill) and of prisms (δ18OIP) compare very well to each other when temporally aligned (R2 = 0.98). The stable carbon isotope values (δ13CDrill; δ13CIP), however, show less agreement (R2 = 0.28), which is likely attributable to different time-averaging of the samples. We discuss how to identify the most suitable prisms for sub-annual paleotemperature reconstructions from disarticulated material using microgrowth patterns and geometrical features of the prisms as proxies for changing growth rates. Finally, we apply the novel sampling strategy to naturally occurring disarticulated prisms from the sediment and compare their intra-prismatic isotope values (δ13CIPS and δ18OIPS) to those of bulk-analyzed prism fragments from the sediment (δ13CBPS and δ18OBPS). Sclerochronological analysis of the prisms from the sediment yields δ18OIPS fluctuations of 1.89‰, virtually identical to the δ18OIP chronologies of the prisms extracted from the shell cross-section (1.90‰). The overall ranges of the δ18OIP and δ18OIPS values are identical (2.60‰) and capture very well the expected seasonal stable oxygen isotope oscillation derived from the δ18ODrill values (2.61‰). The range of the δ18OIPS data is two-fold larger than that of the δ18OBPS values (1.19‰), suggesting a strong effect of time-averaging on the stable oxygen isotope data of the bulk-analyzed prisms fragments. According to our novel statistical model, the resolution of δ18OBPS data can be increased by preferentially analyzing short (ca. 300 μm) individual prisms fragments (at least n = 20).

International audience; Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are recorded in marine sediments. In this contribution, we provide a review of the rapidly developing sub-fields of research, where new advances have been made possibleby technological developments, and by cross-disciplinary work of the scientific community. Following brief historical overviews of the sub-fields, we discuss the latest advances in planktonic foraminifer research and highlight the resulting new perspectives in ocean and climate research. Natural classification based on consistent species concepts forms the basis for analysis of any foraminifer-derived proxy. New approaches in taxonomy and phylogeny of Cenozoic planktonic foraminifers (Section 2) are presented, highlighting new perspectives on sensitivity and response of planktonic foraminifers to the changing climate and environment (Section 4). Calibration of foraminifer-specific data and environmental parameters is improving along with the technical development of probes and the access to samples from the natural environment (Section 3), enhancing our understanding of the ever-changing climate and ocean system. Comprehension of sedimentation and flux dynamics facilitates maximum gain of information from fossil assemblages (Section 5). Subtle changes in the physical (e.g., temperature), chemical (e.g., pH), and biological (e.g., food) conditions of ambient seawater affect the abundance of species and composition of assemblages as well as the chemical composition of the foraminifer shell and provide increasingly-detailed proxy data on paleoenvironments (Section 6).

The influence of climate change on hominin evolution is much debated. Two issues hamper our understanding of this process: the limited hominin fossil record, and incomplete knowledge about hominin spatial occupation of Africa. Here, we analyze the presently known hominin fossil distribution pattern and explore the potential geographic distribution of hominins between ∼4.5 and ∼2.5 Ma. We focus on assessing the relevance of the Coastal Forest of Eastern Africa (CFEA) along the Indian Ocean as a core area for early hominin evolution. Based on biogeographic-phylogeographic data we propose the coastal refuge hypothesis: the CFEA provided a refugium for early hominins in periods of variable climate and strong seasonality during eccentricity maxima. From this refuge, evolved species could disperse inland (e.g. to rift basins) via vegetated humid corridors, whenever onset of stable climate periods with low seasonality during eccentricity minima allowed expansion out of the coastal enclave. We develop a conceptual model in time and space, comparing predictions with climatic and hominin fossil records. The results imply that:1) between ∼4.5 and 3 Ma, ongoing (mostly anagenetic) hominin evolution occurred in the CFEA, punctuated by inland dispersal events at ∼4.4, 4.2, 3.8, 3.5, and 3.2 Ma;2) before ∼3 Ma, the Afar Basin was a (sub)core area often connected to and relatively similar to the CFEA, while other inland areas were more or less marginal for early hominin habitation;3) after ∼3 Ma, Northern Hemisphere Glaciation exerted strong influence by causing latitudinal contraction of the CFEA, leading to habitat fragmentation, isolation of hominin populations and possible cladogenetic evolution.A major challenge for the coastal refuge model is the fact that at present, no (hominin) fossils are known from the CFEA. We consider how this can be explained, and possibly overcome with targeted search efforts. Furthermore we discuss how the model can be tested, e.g. with molecular phylogeography approaches, and used to predict new hominin fossil locations. With this study, we hope to contribute a fresh perspective to the climate-evolution debate, emphasizing the role of climatic stability, length of dry season and vegetation cover to facilitate connectivity between hominin core and marginal habitats.

The South Atlantic Aptian ‘Pre-salt’ reservoirs are formed by a combination of spherulitic carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic chemistries. So far, outcrop analogues characterised by metre-thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact. In particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained, little studied, and hotly debated. To shed light on this conundrum, a spherulitic carbonate-rich, alkaline volcanic lacustrine succession has been analysed at outcrop scale: the Carboniferous East Kirkton Limestone (Scotland). Despite clays being very scarce and limited to layers of amorphous Mg-Si minerals, a diverse array of spherulitic calcitic components were formed, including coated grains, crusts, and build-ups. This setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the ‘Pre-Salt’ subsurface occurrences but divorced from clay influence. The integration of logs, borehole data, outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the East Kirkton lacustrine succession. In this model, calcite spherule nucleation took place at the sediment-water interface in the littoral zone, driven by the co-occurrence of 1) high alkalinity, 2) Ca-Mg rich hydrochemistry, and 3) microbial-derived colloidal exopolymeric substances. These environmental conditions permitted the coeval development of spherulitic cementstone build-ups and spherulitic grainstone-packstone within the wave-agitated zone, and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking. This model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex ‘microbe-solution’ interactions before any reliable facies model is envisaged.