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During the Middle Miocene the Earth’s climate shifted from a warm phase, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder phase associated with the formation of major and permanent Antarctic ice sheets. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma), had significant impact on the composition and structure of major biomes (e.g. Jimenez-Moreno & Suc, 2007) and impacted worldwide ocean circulation (Holbourn et al., 2014) as well as terrestrial temperature and precipitation patterns (e.g. Methner et al., 2020). While the MCO and the subsequent MMCT are well described in marine records, quantitative continental paleoclimate records are still lacking when it comes to constraining the magnitude and rate of terrestrial environmental change. Collectively, δ18O, δ13C and Δ47 data from soil carbonates provide information about past environmental and climatic conditions, such as (seasonality of) precipitation, soil temperature as well as vegetation patterns. The formation of soil carbonates is mainly controlled by the interplay of environmental factors such as soil water composition, soil temperature, and soil CO2. We compare the stable (δ18O, δ13C) and clumped (Δ47) isotopic composition of pedogenic carbonate nodules of the Digne-Valensole Basin (SE France) with time equivalent counterparts from central Europe (Northern Alpine Molasse Basin, Switzerland) and present a ca. 23 – 12.5 Ma biostratigraphically-controlled clumped isotope paleotemperature record from the SW-foreland of the European Alps. Alluvial fan deposition and soil formation in the Digne-Valensole Basin occurred near sea level as documented by the intercalation of marine and continental facies (Cojan et al., 2013). Our Δ47 results from the Digne-Valensole Basin indicate relatively warm and stable carbonate formation temperatures (ca. 32°C) for the Early Miocene (23–19.5 Ma) followed by enhanced temperature fluctuations attaining maximum values at the onset of the MCO. The Digne-Valensole temperature pattern correlates with age-equivalent Δ47 temperatures from the Northern Alpine Foreland Basin. In both records, significant climatic changes can be observed at the onset of the MCO and the MMCT, which are documented by major rapid shifts in paleotemperatures (ca. 15°C within 300 ka). However, the proximity to the Mediterranean Basin is clearly visible in the Digne-Valensole records as expressed in rather high δ18O values of meteoric water that average ca. −3.5 ‰. Combining our data with the Northern Alpine foreland records results in a coherent climate pattern for the Alpine foreland during the Middle Miocene. Cojan et al. (2013) https://doi.org/10.2113/gssgfbull.184.6.583Holbourn et al. (2014) https://doi.org/10.1130/G34890.1Jimenez-Moreno & Suc (2007) https://doi.org/10.1016/j.palaeo.2007.03.040Methner et al. (2020) https://doi.org/10.1038/s41598-020-64743-5

For decades, the search for terrestrial abiotic CH4 has been a central quest in geology and astrobiology. Most of this research has focused on crustal fluid samples collected at surface seeps, hydrothermal vents, and wells. Nonetheless, in such open systems processes like mixing with shallow biotic CH4, oxidation, and diffusion can lead to large uncertainties in the initial composition of deeply originated CH41. Extracting natural CH4 from fluid inclusions entrapped in minerals could overcome the effects of shallow contamination occurring in natural open systems and shed light on the origin of deep CH4 in a wide variety of geodynamic settings2,3. In this abstract, we present a novel approach for bulk off-line fluid inclusion extraction for the analysis of δ13C-CH4 using a Cavity Ring-Down Spectroscopy (CRDS) analyzer (Picarro G2201-i). Two fluid extraction techniques were compared: ball milling in ZrO2 jars and sample crushing in a stainless-steel sealed tube under a piston. The accuracy and precision of the different protocols was evaluated with blanks, CH4 isotopic labelling and interlaboratory comparisons. Blanks and isotopically labelled tests with the ball milling technique suggested that milling speed, and duration, and sample mass and type may strongly affect the CH4 concentrations and isotopic compositions measured by the CRDS analyser. These effects are mainly ruled by the blank production of CH4 –demonstrated by gas chromatography analyses– and potentially other molecules induced by frictional heating. The blank gases may cause interference effects on the absorption bands detected by the CRDS analyser. This effect was marked by a large offset in the δ13C-CH4 measured in the high-range analytical modes of the Picarro G2201-i. The magnitude of the interference was inversely correlated to the CH4 concentration.Other processes such as CH4 diffusion and adsorption may play a role in the observed changes in CH4 concentrations and isotopic compositions. Experimental conditions involving high CH4 concentrations and sample mass could well reproduce CH4 isotopic composition. Crushing in a sealed stainless-steel tube produces lower blank levels compared to ball milling, nevertheless the crushing efficiency and CH4 release is lower due to smaller rock sample size. The presented ball milling protocol provides a simple and fast way to extract and accurately analyse CH4 hosted in fluid inclusions even if great care should be considered for samples with low CH4 concentrations where contamination and interferences can potentially alter the CH4 isotopic signature of natural samples. References 1 - Young et al. (2017). 10.1016/j.gca.2016.12.041 2 - Klein et al. (2019). 10.1073/pnas.1907871116 3 - Grozeva et al. (2020). 10.1098/rsta.2018.0431 This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).

At volcanoes in unrest, the interpretation of geochemical time-series is a major issue for decrypting volcano dynamics and forecast eruptive scenarios. However, interpretation cannot be purely observational and demands the assessment of the main physicochemical features of the hydrothermal system. In the case of La Soufrière of Guadeloupe (FWI) andesitic volcano, a careful analysis of different techniques adopted historically for gas sampling and analysis by the local observatory has allowed us to model degassing and assess gas indicators from non-condensable species in the H2-N2-CH4-He-Ar system available since 2006. Here we report on the nature of discharged gases, resulting from the mixing of atmospheric component and a magmatic-hydrothermal gas evolving along a lineage connecting MORB-like upper mantle and arc-volcano components. We show that along this lineage we can track the hydrothermal build-up of pressure and temperature modulated by magmatic variations, particularly decompression. A careful analysis of inert gas fractionation allows recognizing two main regimes: one is about hydrothermal degassing conditions perturbed by the deep impulsive gas infiltration after magma refilling in a 4 to 8 km deep chamber; the other is determined by ascent of magma batches to a shallower (about 3 km deep) chamber. Further changes of the bulk permeability structure in the hydrothermal reservoir due to fracture sealing and clogging effect may exacerbate observed evolutions but do not represent the primary control of the degassing process. We also show that gas ratios in the H2-He-CH4 subsystem can effectively discriminate and anticipate such tendencies and, particularly, they can be turned into reliable precursors of magma-derived solicitations and set possible thresholds for next crises. The main test is made with reference to the 2013-2014 and 2018 episodes of accelerated unrest: we confirm that the latter is as an aborted phreatic eruption, triggered by the injection of hot magmatic fluids into the magmatic system. On the other hand, for the 2013-2014 period, poorly studied, we document for the very first time the ascent of a small batch of magma which refilled the 3 km deep shallow magma chamber. This triggered seismicity just on top of the brittle-ductile transition. Besides, our method reveals that in 2007-09 an unrest phase similar to the 2018 one occurred, although not marked by the same seismic activity likely because the volcanic system was more sealed and less fractured before the magmatic upward excursion of the 2013-14 phase. Our results and conclusions are suitable for all those volcanic systems at the hydrothermal stage and allow a better definition of unrest scenarios whenever sampling frequency of fumarolic fluids is compatible with the expected transit times of magmatic fluids from magma chambers to surface.

Between 5.97-5.33 Ma, kilometre-thick evaporite units were deposited in the Mediterranean Basin during the so-called Messinian Salinity Crisis (MSC). The MSC was marked by a strongly negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. Knowledge about the contemporary changes in continental and marine circum-Mediterranean environments are still limited to qualitative descriptions in terms of temperature and humidity. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (brGDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma) and compare them with values obtained from Δ47 clumped isotope geochemistry measured on paleosol carbonate nodules found at few locations in the Mediterranean basin. Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using the isoprenoidal GDGT-based TEX86 proxy. The excellently preserved organic biomarkers were extracted from outcrops onshore (Malaga, Sicily, Cyprus) and offshore (DSDP core holes 124 and 134 from the Balearic abyssal plane, hole 374 from the Ionian Basin and hole 376 drilled west of Cyprus) covering a rather vast portion of the Mediterranean Basin.Calculated MATs for the 5.55 to 5.33 Ma time interval show values around 16 to 19 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A holes 374 and 376 are lower, around 13 to 16 ºC. Comparing the brGDGT-MAT values with Δ47-MAT values from carbonate nodules, shows high congruence between both approaches. For the northern Mediterranean Δ47-MAT is 20 ºC and brGDGT-MAT is 19 ºC. For Cyprus Δ47-MAT is 21 ºC and brGDGT-MAT is 18 ºC. Given the very different type of the used paleoproxies, the similarity of the obtained MAT values provides a strong indication of their (cross)validity in sampled sections. Additionally, the measured δ18O values of ~33‰ (VSMOW) for the carbonate nodules used for the Δ47-MAT indicate highly evaporative conditions for the two onland sites where these were collected (Northern Apennines and Cyprus).For samples where the branched and isoprenoid tetraether index was lower than 0.4 we could calculate TEX86 derived SSTs averaging around 27 ºC for all sampled locations, reaching the higher end of the values obtained in the Mediterranean region for the pre-MSC through Uk37 and TEX86 derived SSTs of Tzanova et al. (2015), Vasiliev et al. (2019) and Kontakiotis et al. 2022. Independent of pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase, Stage 3 of the MSC. These elevated temperatures coincide with higher δ2H values measured on alkenones and long chain n-alkanes (both records indicating more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We conclude that between 5.55 to 5.33 Ma the temperatures in the Mediterranean region was similar to present-day conditions, yet the region has suffered from excess evaporation as indicated by combined high δ18O values from carbonate nodules δ2H values from biomarkers.

The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon , are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ 47 and Δ 48 ) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon , modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiological differences in the reproductive systems between Troodon , reptiles, and birds. Troodon and modern reptiles mineralize their eggshells indistinguishable from dual clumped isotope equilibrium, while birds precipitate eggshells characterized by a positive disequilibrium offset in Δ 48 . Analyses of inorganic calcites suggest that the observed disequilibrium pattern in birds is linked to an amorphous calcium carbonate (ACC) precursor, a carbonate phase known to accelerate eggshell formation in birds. Lack of disequilibrium patterns in reptile and Troodon eggshells implies these vertebrates had not acquired the fast, ACC-based eggshell calcification process characteristic of birds. Observation that Troodon retained a slow reptile-like calcification suggests that it possessed two functional ovaries and was limited in the number of eggs it could produce; thus its large clutches would have been laid by several females. Dual clumped isotope analysis of eggshells of extinct vertebrates sheds light on physiological information otherwise inaccessible in the fossil record.

This paper presents new chemical and isotopic data on gases from deep oil and gas fields, bubbling gases, dissolved gases in groundwaters and dry seeps of the Southern Po River Basin (Emilia-Romagna, Italy), aiming to (i) characterize and differentiate the various types of deep natural gases; (ii) identify the source(s) of methane and light hydrocarbons in shallow aquifers and surface gas-rich emissions; (iii) propose a conceptual model of natural fluid migration pathways in the sedimentary prism of the Southern Po River Basin. Based on the isotopic composition of CH4 and C2–C4 n-alkanes, CH4/(C2H6+C3H8) ratio, relative proportion of the C7 hydrocarbons and relative concentration of cyclic compounds with respect to the total cyclic abundance, three main deep reservoirs of hydrocarbons are identified in the subsurface of the Southern Po River Basin: (1) microbial gas hosted in Pliocene-Pleistocene marine sediments, (2) thermogenic gas hosted in Miocene deposits and (3) thermogenic gas produced in Triassic carbonates. Helium isotopes of these deep fluids indicate an almost pure crustal origin (Rc/Ra values = 0.014–0.04), with negligible contributions from mantle-derived helium. A variable contribution of atmosphere-derived fluids is highlighted by low 4He/20Ne (down to 5.42) and 40Ar/36Ar (≤319.5) values. Comparison of chemical and isotopic signatures of deep and surficial hydrocarbon occurrences suggests that methane in shallow groundwaters or gas seeps is sourced by microbial gas migrating upward from deep Plio-Pleistocene reservoirs, with no detectable contributions of Triassic or Miocene thermogenic hydrocarbons. At shallow depths (roughly around 20–50 m.b.g.l.), Plio-Pleistocene microbial methane appears to be mainly stored in anoxic aquifers. However, where CH4 further migrates upwards and reaches aerobic environments (e.g., aquifers or soils), it readily undergoes a process of exothermic microbial oxidation mediated by methanotrophic bacteria. Where the structural architecture of the sedimentary sequence favors the migration of fluids, the methanotrophic biofilter is bypassed and CH4 is discharged through soil diffuse degassing or gas bubbling at water wells. We argue that microbial consumption might be able to bio-sequester significant amounts of Plio-Pleistocene deep-sourced methane in the form of CO2 and biomass. Such process might be widespread in the subsurface of the Southern Po River Basin and, possibly, in other foreland basins worldwide.

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

Fluids emanating from geothermal areas contain trace quantities of methane and other simple hydrocarbons. These hydrocarbons are thought to derive from thermal cracking of organic matter dissolved in circulating meteoric or seawater or found in pre-existing organic-rich sedimentary rocks, but an abiotic origin has also been proposed. We measured the relative abundances of four CH4 isotopologues (12CH4, 13CH4, 12CH3D, and 13CH3D) in hydrothermal gases discharged by steam vents and geothermal wells from Iceland and Nisyros island (Greece) in order to investigate the origin of methane. Measured methane samples yielded consistently low Δ13CH3D values (13CH3D abundance relative to stochastic) of 0.82–1.77‰, which correspond to high apparent temperatures of isotopologue equilibrium ( T Δ 13 CH 3 D = 278–490 °C). Hydrothermal well fluids from the Krafla and Namafjall geothermal fields in Iceland yielded the lowest Δ13CH3D values, and thus the highest Δ13CH3D-based temperatures averaging 438 - 45 + 55 °C. Those samples also show the most pronounced departures in δDCH4 and δ13CCH4 values expected for isotopic equilibrium with respect to δDH2O and δ13CCO2. In contrast, CH4 samples from natural steam vents in other Iceland locations and in Nisyros have slightly higher Δ13CH3D values (with T Δ 13 CH 3 D = 351 - 35 + 42 °C) and have δDCH4 and δ13CCH4 values that are consistent with those expected for isotopic equilibrium with both H2O and CO2. The short fluid residence times (1–50 years) in systems that are exploited for geothermal energy, such as Krafla and Namafjall, combined with the proximity of a hot magma chamber, favor the preservation of kinetic signals. The initial disequilibrium δDCH4 and δ13CCH4 values are consistent with a thermogenic origin from immature organics dissolved in hydrothermally heated groundwater, but an abiotic origin cannot be excluded. The high apparent Δ13CH3D-based temperatures at Krafla and Namafjall could therefore represent nonequilibrium signals associated with either pyrolysis or abiotic generation of CH4 in a superheated vapor or supercritical water phase (>374 °C), considered to exist in the roots of the system above the magmatic heat source. Isotopologue equilibration calculations demonstrate that under such conditions (e.g. > 400 °C) kinetic signals would be erased in days to months, implying rapid migration and quenching of CH4 into the overlying subcritical ( 100 years. Our calculations further reveal that CO2–CH4 isotopic equilibration requires unreasonably long fluid residence times, suggesting that any apparent 13C equilibrium may be coincidental.

Reconstructing long-term continental temperature change provides the required counterpart to age equivalent marine records and can reveal how terrestrial and marine temperatures were related during times of extreme climate change such as the Miocene Climatic Optimum (MCO) and the following Middle Miocene Climatic Transition (MMCT). Carbonate clumped isotope temperatures (T(Δ47)) from 17.5 to 14.0 Ma Central European paleosols (Molasse Basin, Switzerland) display a temperature pattern during the MCO that is similar to coeval marine temperature records. Maximum temperatures in the long-term soil T(Δ47) record (at 16.5 and 14.9 Ma) lag maximum ocean bottom water temperatures, lead global ice volume, and mark the initiation of minimum global ice volume phases. The suggested onset of the MMCT, deduced by a marked and rapid decline in Molasse Basin soil temperatures is coeval with cooling reported in high-latitudinal marine records. This is best explained by a change in the seasonal timing of soil carbonate formation that was likely driven by a modification of rainfall seasonality and thus by a major reorganization of mid-latitude atmospheric circulation across Central Europe. In particular, our data suggest a strong climate coupling between the North Atlantic and Central Europe already in the middle Miocene.

The Eocene, as the warmest epoch during the Cenozoic, has received much attention as it can inform us about the features of global warmth, highly relevant to a “high-CO2” future. However, there is still a lack of knowledge regarding some key features of global warm climates, such as how higher global temperatures might have affected the duration and intensity of seasonality. Furthermore, recognizing seasonal cycles is essential when interpreting proxy data and reconstructing paleo climate, e.g. in order to understand inter-annual bias between proxies. In the current study the seasonal variations in sea surface temperature (SST) and fresh water input into the Anglo-Paris Basin (subjacent areas of the Paleo-North Sea) was investigated. Marginal seas, like the Paleo North Sea, are an important intersection between the continental and marine realm, and are especially sensitive to short-term climate variations.In order to resolve seasonal and perennial changes in SST and freshwater balance, we measured Ba/Ca, δ18O, and the clumped isotopic composition (∆47) of exceptionally well-preserved fossil molluscs. Although δ18O is commonly used for the reconstruction of temperature, its calculation often assumes a constant δ18O value of seawater, which might not be true on seasonal scales and/or within swallow marine basins. In this context, ∆47 was employed to determine the average temperature amplitude, due to its independence from δ18Oseawater. Additionally, Ba/Ca was used to account for periods with enhanced fresh water input, because barium mostly enters the oceans via fluvial systems and could therefor indicate seasonally enhanced and isotopic lighter fresh water input. The bivalve species Venericor planicosta was employed as proxy archive, due to its long life span (10-20 years) and its wide distribution in the Anglo-Paris Basin during the Eocene. The pristinely preserved, aragonitic bivalve shells were sampled by micro-milling (δ18O, ∆47), as well as, laser ablation (Ba/Ca), to generate proxy records with high temporal resolution.The isotopic data reveal well pronounced seasonal oscillation with a sinusoidal shape and a maximum difference of 2‰, from -3,5‰ to -5,5‰. On average, the inter-annual variation of the δ18O record is around 1‰. The Ba/Ca record, on the other hand, shows a flat background with recurring large and sharp peaks. While the baseline Ba/Ca values are around 20 µmol/mol, the peaks can reach up to 300 µmol/mol. The peaks largely fall together with periods of depleted δ18O values. These results hint to a possible seasonal bias of temperature records in the Anglo-Paris basin based purely on δ18O, due to variable δ18O of seawater. This is further implied by the back-calculation of δ18Oseawater from ∆47 measurements, revealing a range from 2‰ to -4‰.

Quantifying surface elevation over geological time is essential for reconstructing coupled climatic and mountain building processes. Surface uplift of an orogen, such as the European Alps, results from the interplay between subsurface geodynamic processes and climate-induced denudation. Although being one of the most studied mountain ranges worldwide, knowledge about the elevation history of the European Alps is still scarce. Stable isotope paleoaltimetry is a robust tool to reconstruct paleoelevations of orogens. The method is based on the systematic inverse relationship of isotope ratios of oxygen (δ18O) and hydrogen (δD) in precipitation with elevation. Recent stable isotope paleoaltimetry studies that focused on the Central Alps indicate elevations locally exceeding 4 km during the Mid-Miocene. Here, we reconstruct past Alpine surface elevations by applying stable isotope paleoaltimetry coupled with clumped isotope, T(Δ47), temperature reconstructions in Miocene paleosols of the Alpine foreland basins. Knowledge of low-elevation (near sea level) temperature conditions allows to refine low-elevation, near sea level estimates for δ18O in precipitation. Contrasting these low-elevation isotope in precipitation values with age equivalent records from high elevation counterparts hence permits calculation of surface elevation differences between the foreland basin and the orogen interior. With a spatio-temporally enhanced coverage of the European Alps, we present a long-term terrestrial climate record covering the time interval between ca. 23 and 14 Ma including sites in the Western and Central Alps. Pedogenic carbonate nodules from paleosols of the Digne-Valensole basin (Western Alps, France) indicate relatively warm and stable temperatures (ca. 26°C) for the early Miocene (23-20 Ma) followed by enhanced temperature variability with maximum values of 34°C at ca. 16.5 Ma. By contrasting temperature-corrected foreland basin pedogenic carbonate δ18O values from the Digne-Valensole Basin with δD values of dated, clay-bearing fault gouge from the Periadriatic Fault in Val Morobbia (Switzerland), we conclude that the stable isotope paleoaltimetry data permit peak elevations of 4-5 km in the Central Alps during the earliest Miocene (ca. 23 Ma).ReferencesKrsnik et al., 2021: SED, doi: 10.5194/se-2021-59Zwingmann & Mancktelow, 2004: EPSL, doi: 10.1016/j.epsl.2004.04.041

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

The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and, ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives only provide a low temporal resolution (ca. 15 years), precluding the ability to identify changes on inter-annual and quasi-decadal timescales. Here, we present a new, high-resolution reconstruction using shells of freshwater pearl mussels, Margaritifera margaritifera, from three streams in northern Sweden. We present seasonally to annually resolved, calendar-aligned stable oxygen and carbon isotope data from 10 specimens, covering the time interval from 1819 to 1998. The bivalves studied formed their shells near equilibrium with the oxygen isotope signature of ambient water and, thus, reflect hydrological processes in the catchment as well as changes, albeit damped, in the isotope signature of local atmospheric precipitation. The shell oxygen isotopes were significantly correlated with the North Atlantic Oscillation index (up to 56 % explained variability), suggesting that the moisture that winter precipitation formed from originated predominantly in the North Atlantic during NAO+ years but in the Arctic during NAO− years. The isotope signature of winter precipitation was attenuated in the stream water, and this damping effect was eventually recorded by the shells. Shell stable carbon isotope values did not show consistent ontogenetic trends, but rather oscillated around an average that ranged from ca. −12.00 to −13.00 ‰ among the streams studied. Results of this study contribute to an improved understanding of climate dynamics in Scandinavia and the North Atlantic sector and can help to constrain eco-hydrological changes in riverine ecosystems. Moreover, long isotope records of precipitation and streamflow are pivotal to improve our understanding and modeling of hydrological, ecological, biogeochemical and atmospheric processes. Our new approach offers a much higher temporal resolution and superior dating control than data from existing archives.

High-precision analysis of the excess abundance (relative to the stochastic distribution) of mass 48 isotopologues in CO2 evolved from acid digestion of carbonates (∆48) has not been possible until recently due to the relatively low natural abundance of 18O. Here we show that the 253 Plus™ gas source mass spectrometer equipped with Faraday cups and 1013 Ω resistors can perform combined ∆47 and ∆48 analyses on carbonates with external reproducibilities (1SD) of 0.010 ‰ and 0.030 ‰, respectively. ~10 mg aliquots of five carbonate reference materials (ETH 1, ETH 2, ETH 3, ETH 4, and Carrara) are digested with phosphoric acid at 90 °C using a common acid bath. The evolved CO2 is purified using an automated gas preparation system (including cryotraps and a GC) and analyzed for its ∆47 and ∆48 compositions using the dual inlet system of a 253 Plus™ gas source mass spectrometer. Raw ∆47 and ∆48 values are finally normalized to the Carbon Dioxide Equilibrium Scale (CDES). In ∆47, CDES 90°C vs. ∆48, CDES 90°C space, calcite reference materials Carrara, ETH 3 and ETH 4 agree with the equilibrium curve for calcite after adding semi-empirically determined 90 °C acid fractionation factors of 0.196 ‰ (for ∆47) and 0.136 ‰ (for ∆48) to theoretical ∆63 and ∆64 data. Agreement between measured and theoretically expected ∆48, CDES 90°C highlights the accuracy of our high-precision clumped isotope analytical setup. Combined analysis of the abundances of mass 47 and mass 48 isotopologues in CO2 evolved from acid digestion of natural carbonates has excellent potential for the determination of accurate and highly precise paleotemperatures as well as for the identification of rate-limiting kinetic processes involved in biomineralization. A formation temperature of 15(±2) °C is obtained on the 95 % confidence level for the Upper Cretaceous chalk sample ETH 3.

Clumped isotope data from carbonated apatite from in vivo and in vitro samples are presented to refine the relationship between mineral growth temperature and carbonate clumped isotopic composition (Δ47). Δ47, δ18O and δ13C data were obtained from phosphoric acid digestion (T = 110 °C) of chemically untreated teeth from an African elephant, Greenland sharks, sand tiger sharks and synthetic apatites. These data cover a temperature range between 1 °C and 80 °C and enlarge the calibration dataset presented in Wacker et al. (2016) by a factor of five. Taxon-specific analyses of tooth enamel(oid) and dentine reveal that both tissues show identical Δ47 values even though the content of organic matter differs by an order of magnitude. The following Δ47 temperature calibration for (bio)apatite is derived (R2 = 0.9924, p-value Δ 47 C D E S 110 = 0.0325 ( ± 0.0012 ) × 10 6 / T 2 + 0.2137 ( ± 0.0124 ) ( w i t h T i n K a n d Δ 47 i n ‰ ) This calibration becomes indistinguishable from a reprocessed empirical calibration of calcite made in the same laboratory if a difference of the acid fractionation factors (AFF) of 0.110‰ between 25 °C and 110 °C is considered. The measured AFF for bioapatite matches the one that is extrapolated from experimental data on calcite and aragonite. The oxygen isotope fractionation between structural carbonate in the synthesized carbonated hydroxylapatites (CHAP) and water between 7 °C and 80 °C closely follows the temperature dependence for the calcite-water system. It is described by the following (CHAP-water) equation (R2 = 0.997, p-value 1000 l n ( α C H A P - w a t e r ) = 17.23 ± 0.59 × 10 3 × T - 1 - 27.28 ( ± 1.73 ) ( w i t h T i n K ) Both calibrations are applied to shark teeth from a modern Greenland shark and a fossil megatooth shark (Carcharodon megalodon) specimen to reconstruct the apparent Δ47-based habitat temperature of C. megalodon (19 ± 4 °C) and the oxygen isotopic compositions of seawater.

Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth’s surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope δ-δ paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5 °C) yield a near sea level precipitation δ18Ow value of −5.8 ± 0.2 ‰ and in conjunction with the high-Alpine phyllosilicate δD record suggest that the region surrounding the SFZ attained surface elevations of > 4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between −4.2 and −7.6 ‰ for the Northern Alpine Foreland Basin.

Hyrrokkin sarcophaga is a parasitic foraminifer that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Lophelia pertusa. Here, we present measurements of the elemental and isotopic composition of this parasitic foraminifer for the first time, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe micro analysis (EPMA) and mass spectrometry (MS).Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr/Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest L. pertusa, which could be an indication that dissolved host carbonate material is utilised in shell calcification, given that the aragonite of L. pertusa has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on L. pertusa, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn/Ca ratios in foraminifers that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions.While our measurements provide an interesting insight into the calcification process of this unusual foraminifer, these data also indicate that the geochemistry of this parasitic foraminifer is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.

The Miocene experienced both, ice-house periods with continental ice-sheets covering both poles and warm greenhouse conditions with strongly increased global temperature, glacier retreat and sea-level rise. The Mid-Miocene Climatic Optimum (MMCO) is the most pronounced warming event in the last 24 Ma, standing out in a time of protracted cooling. The MMCO is marked by a period of intensive global warming between ca. 17 and 15 Ma. The subsequent Mid-Miocene Climate Transition (MMCT), in contrast, was affected by global temperature decline, growth of Antarctic ice sheets, sea level fall and marine biota overturn.Miocene climate conditions were intensely studied on both, global and regional scales, based on i.a. marine isotope records and continental paleobotanical and mammalian fossil data sets. Despite the dense data sets continental Miocene temperature evolution still remains unclear owing to a large range of inferred temperatures and/or poor age constraints of the associated records.Here, we present a long-term terrestrial climate record that covers the time interval between ~20 and ~13 Ma and is based on stable (δ18O) and clumped isotope (Δ47) geochemical data. We apply Δ47 thermometry on terrestrial foreland basin sediments to reconstruct the Middle Miocene continental temperature evolution for central Europe. Pedogenic carbonates from well dated fossil soils from several sites in the Northern Alpine Foreland Basin (Switzerland) reveal warm and stable temperatures for the early Miocene (20 – 19 Ma), followed by overall strongly enhanced variability in temperatures with maximum values attained between ca. 17 and 14 Ma. We observe a highly dynamic transition to cooler climates at the end of the MMCO and a subsequent rapid temperature decline of approximately 20°C after 14 Ma during the MMCT. The highly variable temperature patterns during the cooling period coincide with phases of high seasonality in the precipitation pattern as derived from oxygen isotope compositions of soil water.

Geochemical records from incremental carbonate archives, such as fossil mollusk shells, contain information on climate and environmental change at the resolution of days to decades (e.g. Schöne and Gillikin, 2013; Ivany, 2012). These high-resolution paleoclimate data, providing snapshots of past climate change on a human scale, complement more conventional reconstructions on a geological timescale of thousands to millions of years. Recent innovations in geochemical techniques such as high-resolution trace element and clumped isotope analyses provide the unique potential to improve the accuracy and resolution of these high-resolution climate reconstructions in the near future (see e.g. de Winter et al., 2020a; b; Caldarescu et al., 2021). However, to be able to make the most out of these new techniques requires a more detailed understanding of the timing and mechanisms of mollusk shell growth as well as the relationship between environment and shell chemistry on daily to weekly timescales.The UNBIAS (UNravelling BIvAlve Shell chemistry) project combines investigations on lab-grown modern bivalve shells with reconstructions based on fossil shell material from past greenhouse periods in an attempt to improve our understanding of short-term temperature variability in warm climates. Samples from cultured shells labeled with a novel trace element spiking method are used to calibrate accurate temperature reconstructions from bivalve shells using the state-of-the-art clumped isotope method. As a result, we present a temperature calibration of clumped isotope measurements on aragonitic shell carbonates. New statistical routines are developed to accurately date microsamples within shells relative to the seasonal cycle (ShellChron; de Winter, 2020) and to strategically combine these microsamples for seasonal reconstructions of temperature and salinity from fossil shells (seasonalclumped, de Winter et al., 2020c; de Winter, 2021). We present the first results of this integrated seasonal reconstruction approach on fossil bivalve shells from the Pliocene Warm Period and Late Cretaceous greenhouse of northwestern Europe as well as an outlook on future plans within the UNBIAS project. ReferencesCaldarescu, D. E. et al. Geochimica et Cosmochimica Acta 294, 174–191 (2021).de Winter, N. J. ShellChron v0.2.8: Builds Chronologies from Oxygen Isotope Profiles in Shells. (2020).de Winter, N. J. seasonalclumped v0.3.2: Toolbox for Seasonal Temperature Reconstructions using Clumped Isotope Analyses. (2021).de Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020a).de Winter, N. J. et al. Nature Communications in Earth and Environment (in review; 2020b) doi:10.21203/rs.3.rs-39203/v2.de Winter, N., Agterhuis, T. & Ziegler, M. Climate of the Past Discussions 1–52 (2020c) doi:https://doi.org/10.5194/cp-2020-118.Ivany, L. C. The Paleontological Society Papers 18, 133–166 (2012).Schöne, B. R. & Gillikin, D. P. Palaeogeography, Palaeoclimatology, Palaeoecology 373, 1–5 (2013).

Carbonated hydroxy-apatite (CHAP) was experimentally synthesized in batch-type set-ups by mixing of calcium (Ca)- and phosphate-bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11° and 65°C (Gussone et al., 2020). Compositional changes of the experimental solution and solid phase products were followed by elemental analysis, Raman spectroscopy, scanning-electron microscopy, and powder XRD. In the mixing experiments, crystallization of CHAP took place following the precipitation of metastable brushite as precursor that was then transformed into CHAP. In the transformation experiments using synthetic calcite as a precursor phase it was found that the reaction at pH values between 7.5 and 7.9 occurs via the direct replacement of calcium carbonate by CHAP.Calcium isotope fractionation led to an enrichment of the light isotope in the solid CHAP compared to the aqueous solution by about -0.5 to -1.1 ‰, independent from the experimental approach, and the magnitude was essentially independent of temperature. The metastable brushite formed prior to transformation to CHAP showed a reduced fractionation compared to the CHAP. The observed Ca isotope fractionation into the CHAP lattice resembles that of natural phosphorites and lies within the range of the view existing theoretical and experimental studies. Reference: Gussone N., Böttcher M.E., Conrad A.C., Fiebig J., Pelz M., Grathoff G., Schmidt B.C. (2020) Calcium isotope fractionation upon experimental apatite formation. Chem. Geol., 551, 119737The study was supported by German Science Foundation (DFG) to M.E.B and J.F. within the EXCALIBOR project (BO1548/8 and FI 948/7), and to N.G. (GU1035/10), and by Leibniz IOW.

Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth‐system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I‐CDES) values for Intercarb‐Carbon Dioxide Equilibrium Scale., Key Points The exclusive use of carbonate reference materials is a robust method for the standardization of clumped isotope measurementsMeasurements using different acid temperatures, designs of preparation lines, and mass spectrometers are statistically indistinguishableWe propose new consensus values for a set of seven carbonate reference materials and updated guidelines to report clumped isotope measurements

The Δ47 (paleo)thermometer has opened a new avenue to determine carbonate formation temperatures independent of the oxygen isotopic composition of the fluid from which the carbonate crystallized. A major limitation of this thermometer is related to kinetic effects if homogeneous isotopic equilibrium is not attained during carbonate precipitation. Dual clumped isotope thermometry – the high-precision analysis of Δ48 along with Δ47 in CO2 evolved from phosphoric acid digestion of carbonates – makes it possible to resolve temperature from the kinetic information recorded in an individual carbonate phase. Therefore, it provides a new opportunity to identify (bio)mineralization pathways and to determine carbonate formation temperatures devoid of a kinetic bias, based solely on isotopic analysis of a single carbonate phase. Identification of the nature and extent of kinetic effects as well as the reconstruction of accurate formation temperatures requires knowledge of the position of equilibrium in Δ47 vs Δ48 space. Here, we present Δ47 and Δ48 data of carbonates that were previously considered as having crystallized closest to equilibrium in a temperature range of 8 to 1100 °C. Across this range, the temperature dependences of Δ47 and Δ48 are best expressed by the following fourth order polynomials of 1/T: Δ47 (CDES 90) (‰) = 1.038 (−5.897 1/T − 3.521 103 1/T2 + 2.391 107 1/T3 − 3.541 109 1/T4) + 0.1856 Δ48 (CDES 90) (‰) = 1.028 (6.002 1/T − 1.299 104 1/T2 + 8.996 106 1/T3 − 7.423 108 1/T4) + 0.1245 with CDES 90 representing the Carbon Dioxide Equilibrium Scale at a reaction temperature of 90 °C. In its entire temperature range, our Δ47 (CDES 90) - T - relationship agrees within 2 ppm with two previous Δ47 (I-CDES) - T - relationships reported by Jautzy et al. (2020) and Anderson et al. (2021). Accuracy of our proposed Δ47 (CDES 90) − Δ48 (CDES 90) equilibrium relationship is independently confirmed by additional dual clumped isotope data of experimental and geothermal carbonates which precipitated from potentially equilibrated dissolved inorganic carbon pools at a temperature range of 25–100 °C. Furthermore, we reprocessed original dual clumped isotope data of natural carbonates (Bajnai et al., 2020) and compared their composition to the position of equilibrium in Δ47 vs Δ48 space. These results corroborate preliminary evidence that the hydration/hydroxylation reactions became rate-limiting during the calcification of a speleothem-like sample, a warm water coral, a cold water coral and a brachiopod, finally evoking significant departures of carbonate-Δ47 and -Δ48 from dual clumped isotope equilibrium. An anti-clumped Δ48 value of −419 (±16) ppm (95% confidence interval level) is obtained for a technical calcite that was precipitated by the injection of CO2 into a Ca(OH)2-saturated solution. Its negative Δ48 value largely arises from a combinatorial effect, i.e. the carbonate oxygen derives from two sources with different bulk isotopic compositions. Besides the identification of the nature and the extent of (bio)mineralization kinetics and the reconstruction of carbonate formation temperatures unbiased by kinetics, dual clumped isotope analysis, therefore, allows tracing the isotopic heterogeneity of oxygen pools contributing to carbonate formation.

Upwelling within the Eastern Equatorial Pacific (EEP) Ocean is a key factor for the Earth's climate because it supports >10% of the present‐day biological production. The dynamics of upwelling in the EEP across the Plio‐Pleistocene transition—an interval particularly relevant for understanding near‐future warming due to Anthropocene‐like atmospheric carbon‐dioxide levels—have been intensively studied for the region east of the East Pacific Rise. In contrast, changes of the equatorial upwelling regime in the open Pacific Ocean west of this oceanographic barrier have received markedly less attention. We therefore provide new proxy records from Ocean Drilling Program Site 849 located within the EEP open‐ocean upwelling regime. Our target interval (∼3.35–2.0 Ma) covers the Plio‐Pleistocene transition characterized by the intensification of Northern Hemisphere Glaciation (iNHG). We use benthic δ18O values to generate a new, high‐resolution age model for Site 849, and sand‐accumulation rates together with benthic δ13C values to evaluate net export production. Although showing temporary substantial glacial‐interglacial variations, our records indicate stability in net export production on secular timescales across the iNHG. We suggest the following processes to have controlled the long‐term evolution of primary productivity at Site 849. First, nutrient export from the high latitudes to the EEP; second, a successive shoaling of the Pacific nutricline during the studied interval; and third, a simultaneous reduction in dust‐borne iron input., Key Points: Glacial‐interglacial change in net export production at East Pacific Site 849 from ∼3.35 to 2.0 Ma. No secular change in net export production in the East Pacific across the Plio‐Pleistocene transition. Net export production on secular timescales regulated by nutrient content of upwelled waters, nutricline dynamics, and iron fertilization., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, Trond Mohn Foundation

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

Sea-level rise resulting from the instability of polar continental ice sheets represents a major socioeconomic hazard arising from anthropogenic warming, but the response of the largest component of Earth’s cryosphere, the East Antarctic Ice Sheet (EAIS), to global warming is poorly understood. Here we present a detailed record of North Atlantic deep-ocean temperature, global sea-level, and ice-volume change for ∼2.75 to 2.4 Ma ago, when atmospheric partial pressure of carbon dioxide (pCO2) ranged from present- day (>400 parts per million volume, ppmv) to preindustrial (

Iron objects are among the most abundant type of metal artefacts in the archaeological record and help to deepen our understanding of past societies and their technologies. However, sampling of them is often problematic due to the destructive character of most analytical methods. In this study, iron and oxygen isotope compositions of iron artefacts from marine and water under-saturated oxidising environments were analysed in a first attempt to gather artefact information from the corrosion layer without sampling the object directly. No Fe isotope fractionation between artefact and its corrosion products was recognised for both environments but cannot be excluded for marine environments. Hence, the artefact’s Fe isotope composition can be determined from the corrosion layer. This allows the characterisation of artefacts which cannot be sampled directly. Because the available data precluded a clear identification of the underlying processes, possible fractionation mechanisms resulting in this situation are presented. Furthermore, the results of this study indicate that corrosion products have the same oxygen isotope composition as their source water. As for marine corrosion, general absence of oxygen isotope fractionation could not be manifested here, because only a small sample size was available for the present study. However, a complex interplay of many parameters governs the oxygen isotope compositions of corrosion products on metallic iron. Especially oxidising environments above the water table have a strong impact on the oxygen isotope composition of the corrosion layer. The first-order controlling mechanisms, such as evaporation, are set by the local environment and cannot be reconstructed. Therefore, the oxygen isotope composition of corrosion products seems to bear no valuable potential for archaeometallurgical research.

Reconstructing past elevations of mountain ranges improves our understanding of crustal- and mantle-scale geodynamic processes involved in formation of orogenic belts. Recent studies suggest that slab breakoff beneath the Central Alps occured ~30 Ma ago (e.g. Schlunegger and Castelltort, 2016), while the breakoff reached the Eastern Alps about 10 Ma later (~20 Ma, e.g. Handy et al., 2015). The proposed west-to-east slab tear migration would imply variations in topography. This raises the question of a diachronous surface uplift history for the Central and Eastern Alps. Although being extremely well studied over the last century and serving as a prime exemple for orogenic belt evolution, there are very few investigations addressing the Neogene paleoelevation history of the European Alps. Obtained paleoelevation constraints suffer from inconsistency and range from average elevations of 2300 m (Kocsis et al., 2007) to at least 5000 m (e.g. Sharp et al., 2005).In order to provide quantitative robust paleoelevation estimates for the Mid-Miocene Central Alps we applied stable isotope paleoaltimetry on authigenic soil carbonates from the Northern Alpine Foreland Basin (NAFB) and contrast these with syntectonic high-Alpine fault zone mica. This δ-δ paleoaltimetry approach benefits from the advantage of comparing a low-elevation site and a high-elevation site of the same age which allows us to circumvent the basic issue of climate bias in paleoaltimetry studies.We obtained stable isotope (δ18O) records of pedogenic carbonate from the Swiss Molasse Basin and δD values of fault mica from the Simplon Fault Zone, for the Middle Miocene (15.5 – 14.0 Ma). The key element in conducting stable isotope paleoaltimetry is the prevailing temperature during low-elevation proxy material formation. Here we present new Mid-Miocene paleoelevation data for the European Central Alps based on precisely defined clumped isotope (∆47) derived carbonate formation temperatures and new low-elevation stable isotope records. A conservative approach renders Mid-Miocene Central Alps mean elevation of approximately 4000 m, which contrasts modern Alpine topography with average elevations of ca. 2000 m in the Central Alps (Kühni and Pfiffner, 2001).

Reaction kinetics involved in the precipitation of carbonates can introduce large scatter and inaccuracies in the temperatures derived from their δ18O and ∆47 values. Advances in mass spectrometry instrumentation recently enabled high-precision analysis of the 18O–18O clumping in carbonate minerals (∆48), despite the relatively low natural abundance of 12C18O18O, the main isotopologue contributing to the ∆48 signal (1). Measurements of ∆48, when combined with ∆47, can yield additional insights into kinetic effects and the carbonate formation environment (2).Here we report high-precision ∆47 and ∆48 values of speleothem carbonates, modern coral skeletons, a brachiopod, and a belemnite. We constrained equilibrium in ∆47 vs ∆48 space by anchoring empirically derived ∆47 vs temperature and ∆48 vs temperature relationships to a Devils Hole mammillary calcite, known to be precipitated at extremely slow rates at a constant 33.7(±0.8) °C and water oxygen isotope composition. Our results, compared to theoretical predictions, provide the most substantial evidence to date that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Data from an ancient belemnite imply it precipitated near isotopic equilibrium and confirm the warmer-than-present temperatures at Early Cretaceous southern high latitudes. The presence of similar kinetic departure in a brachiopod but not in a belemnite suggests that the current discrepancy between belemnite and brachiopod-based temperature estimates in the geologic record is most likely related to a greater kinetic bias in the isotopic composition of brachiopod shells.We demonstrate that the combined clumped isotope method makes it possible to identify carbonates that did not precipitate in thermodynamic equilibrium from their parent water. Our results highlight the potential that the combined clumped isotope analyses hold for accurate paleoclimate reconstructions and the identification of the kinetic fractionation processes dominant in carbonate (bio)mineralisation.(1) Fiebig et al. (2019), https://doi.org/10.1016/j.chemgeo.2019.05.019(2) Guo, W. (2020), https://doi.org/10.1016/j.gca.2019.07.055

Significance Clumped and stable isotope data of paleosol carbonate and fossil tooth enamel inform about paleoenvironments of Early Pleistocene hominins. Data on woodland- vs. grassland-dominated ecosystems, soil temperatures, aridity, and the diet of Homo rudolfensis and Paranthropus boisei ca. 2.4 Ma show that they were adapted to C3 resources in wooded savanna environments in relatively cool and wet climates in the Malawi Rift. In contrast, time-equivalent Paranthropus living in open and drier settings in the northern East African Rift relied on C4 plants, a trend that became enhanced after 2 Ma, while southern African Paranthropus persistently relied mainly on C3 resources. In its early evolutionary history, Homo already showed a high versatility, suggesting that Pleistocene Homo and Paranthropus were already dietary generalists., New geochemical data from the Malawi Rift (Chiwondo Beds, Karonga Basin) fill a major spatial gap in our knowledge of hominin adaptations on a continental scale. Oxygen (δ18O), carbon (δ13C), and clumped (Δ47) isotope data on paleosols, hominins, and selected fauna elucidate an unexpected diversity in the Pleistocene hominin diet in the various habitats of the East African Rift System (EARS). Food sources of early Homo and Paranthropus thriving in relatively cool and wet wooded savanna ecosystems along the western shore of paleolake Malawi contained a large fraction of C3 plant material. Complementary water consumption reconstructions suggest that ca. 2.4 Ma, early Homo (Homo rudolfensis) and Paranthropus (Paranthropus boisei) remained rather stationary near freshwater sources along the lake margins. Time-equivalent Paranthropus aethiopicus from the Eastern Rift further north in the EARS consumed a higher fraction of C4 resources, an adaptation that grew more pronounced with increasing openness of the savanna setting after 2 Ma, while Homo maintained a high versatility. However, southern African Paranthropus robustus had, similar to the Malawi Rift individuals, C3-dominated feeding strategies throughout the Early Pleistocene. Collectively, the stable isotope and faunal data presented here document that early Homo and Paranthropus were dietary opportunists and able to cope with a wide range of paleohabitats, which clearly demonstrates their high behavioral flexibility in the African Early Pleistocene.

Abundance patterns of planktic and benthic foraminifera from the middle to upper Albian of tropical Atlantic Ocean Drilling Program Site 1258 (Demerara Rise) display a pronounced shift between two clearly distinguishable assemblages: (1) a foraminiferal fauna dominated by coiled taxa, which is inferred to represent a deep and/or weak oxygen minimum zone, and (2) abundant clavate and biserial taxa, inferred to record a shallow and/or strong oxygen minimum zone at Demerara Rise. The entire sequence is rich in organic matter (3–6 wt% TOC) of a marine phytoplankton origin (δ 13 C ∼ −28‰), consistent with a highly productive region. Both the high productivity and changes in foraminiferal assemblages are consistent with changes in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ) over the South American continent. Movements of the ITCZ are proposed to reduce the amount of runoff during the 'clavate-dominated' cycles, leading to the intensification of upwelling and therefore a stronger oxygen minimum zone compared to the intervals dominated by coiled foraminifera. We have previously found a similar hydrographic cycle in Turonian to Coniacian sections from the same area suggesting that this climate cyclicity and palaeogeography was long-lived off NE South America (∼15 million years). Due to the stratigraphic position of the interval with high abundances of clavate planktic foraminifera and the inferred strong oxygen minimum zone, it is tentatively proposed that this interval represents a local expression of the OAE 1c event within the long-living Demerara Rise upwelling system.

International audience; The mid-Pleistocene Transition (MPT; approx. 1.2-0.7 Ma), is characterized by growing Northern Hemisphere ice sheets and the shift from a 41 kyr to a 100 kyr glacial-interglacial cyclicity. Concomitant to the growth of large ice sheets, atmospheric and oceanic circulation pattern have changed. One key feature of the North Atlantic is the wind-driven Subtropical Gyre, a major provider of heat and moisture for continental Europe. Here, we investigate changes in the strength and spatial configuration of the Subtropical Gyre during the MPT and its impact on the continental moisture balance. To reconstruct Subtropical Gyre dynamics, we conducted paired δ18O and Mg/Ca analyses on the deep-dwelling foraminifera Globorotalia inflata from Iberian Margin Site U1385 yielding thermocline temperature (Ttherm) variability between 1400 and 500 ka at the eastern boundary of the Subtropical Gyre. Long-term trends of Ttherm at Site U1385 oppose the North Atlantic climatic evolution of progressively intensified glacials during the MPT. Particularly, glacials MIS 20 and 18 were marked by warm thermocline waters off Iberia. We infer that a southward shift of the (sub)polar front displaced the source region of thermocline waters within the Subtropical Gyre from high to mid-latitudes. In addition, a strong Mediterranean Outflow Water production during the MPT caused the advection of warm waters to Iberia. Humid conditions during MIS 20 and 18 in SE Europe indicate that atmospheric moisture derived from this warm water might have been advected deep into continental Europe and contributed to enhanced growth of Alpine glaciers.

Holocene climate dynamics have strongly influenced precipitation patterns in the Eastern Mediterranean region. This holds particularly true for the ‘8.2 kyr BP climatic event’, arguably the strongest perturbation of early to mid-Holocene climate. Here we present a biomarker record of leaf wax-derived n -alkane distributions and stable isotopic composition of total organic carbon (δ 13 C TOC ) along with palynological data from the fen peat archive of Tenaghi Philippon (TP), NE Greece, spanning the interval from 8.7 to 7.5 kyr BP. Our record documents the response of in situ vegetation within the Philippi peatland to changing hydrological conditions, and addresses the applicability of organic proxies such as the ‘aquatic index’ ( P aq ), average chain length (ACL) and δ 13 C TOC as indicators of peat surface moisture conditions at the study site. The long chain n -alkanes ( n -C 27 , n -C 29 and n -C 31 ) typical of vascular terrestrial plants, dominated the peat sequence. A period of relatively dry surface conditions, indicated by low values of P aq and elevated ACL values, in concert with elevated δ 13 C TOC values, preceded the 8.2 kyr BP climatic event from ca. 8.7 to 8.2 kyr BP. Slightly wetter, more humid conditions, suggested by an increase in P aq as well as reduced ACL and δ 13 C TOC values, characterized the interval of the 8.2 kyr BP climatic event. Notably, the increase in surface wetness, as indicated by the biomarker record, coincided with a marked rise in fern spore proportion as well as increasing proportion of pollen from aquatic taxa. Following the 8.2 kyr BP event, a distinct change in paleohydrology at TP became apparent from ca. 7.9 kyr BP onward. An increase in the abundance of the mid-chain length n -alkanes ( n -C 23 and n -C 25 ), indicative of an increased contribution from aquatic plants to the sediment, together with a steep increase in P aq and a decrease in ACL, as well as variation in δ 13 C TOC , imply considerably elevated surface moisture levels, likely caused by the increased activity of the karstic system of the surrounding mountains. Collectively, the biomarker proxies and pollen data reveal a concise picture of changing moisture conditions at TP in response to the 8.2 kyr BP climatic event.

The late Pliocene/early Pleistocene intensification of Northern Hemisphere Glaciation (iNHG) represents the most recent major tipping point in Earth's climate history. In the equatorial Pacific, the iNHG has been suggested to mark the transition from a warm Pliocene climate state, in which the Pacific warm pool was greatly expanded relative to today giving rise to a surface ocean temperature field akin to modern El Nino conditions, to a climate state with strong upwelling in the east of the basin and stronger zonal temperature gradients. Here we examine this transition by presenting new high-resolution (∼800 yr) planktic foraminiferal Mg/Ca- and δ18δ18O-based sea-surface temperature (SST) and salinity (SSS; based on δ18Oδ18O residuals [δ18Oivc-swδ18Oivc-sw]) records from Eastern Equatorial Pacific (EEP) Ocean Drilling Program Site 849 spanning ∼2.75–2.4 Ma. Our study interval contains the first large-amplitude (∼1‰ in benthic δ18δ18O) early Pleistocene glacial–interglacial cycles (Marine Isotope Stages 100–96) representing the culmination of iNHG. In this study we investigate west-to-east equatorial Pacific SST and SSS gradients. We find that the zonal SST gradient increased by ∼1.5 °C from ∼2.75 to ∼2.4 Ma through EEP cooling. No glacial–interglacial pattern is seen in this gradient. On the other hand, we document obliquity-paced oscillations in the δ18Oivc-swδ18Oivc-sw (SSS) gradient. We hypothesize that these oscillations originated from a response to a glacial southward and interglacial northward migration of the Intertropical Convergence Zone over the EEP.