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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

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.

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

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.

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.

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).

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

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 (

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.

It has recently been shown that the clumped isotopic composition (Δ47) of carbonate-bearing hydroxyapatite (CHAP) from teeth and bones reveals important information about the body temperature of vertebrates (Eagle et al., 2010, 2011). In this study we reinvestigate the temperature dependence of Δ47 in CHAP, extending the temperature range from 2 to 59 °C. In addition, the effects of chemical pre-treatment of CHAP on its bulk and clumped isotopic composition are studied. CHAP is best reacted with phosphoric acid at 90 to 110 °C minimizing the potential of evolved CO2 or reaction intermediates to re-equilibrate with traces of water in the acid environment. Reaction at 110 °C ensures that digestions of CHAP samples are complete within 60 min. We determined a Δ47 ⁎ 90–110 value of 0.032 ± 0.008‰ that is - within errors - indistinguishable from a Δ47 ⁎ 90–110 value of 0.019 ± 0.007‰ received for aragonite. For tooth enamel pre-treated with H2O2 lower Δ47 values, and higher δ18O and δ13C values were measured than for pre-treated tooth dentine. In addition, similar trends were observed for pre-treated dentine and bone material: higher Δ47 values, and lower δ18O and δ13C values were determined compared to untreated samples. A new tentative clumped isotope temperature calibration based on a synthetic apatite, untreated tooth enamel of an African elephant and enameloid from teeth of a Greenland shark is presented using a reaction temperature of 110 °C. It follows the equation: Δ47 = 0.0320 (± 0.0022) × 106/T2 + 0.1977 (± 0.0259) (Δ47 in ‰ and T in K). The slope of this regression line is identical to those previously obtained from 90 °C digestions of calcite and/or aragonite in several laboratories (e.g., Henkes et al., 2013; Wacker et al., 2014; Defliese and Lohmann, 2015). The Δ47 data of untreated enamel(oid) samples reacted at 90 °C closely match a Δ47-1/T2 relationship for calcite that was made at the same digestion temperature (Wacker et al., 2014). These preliminary results suggest that calcite calibrations made at a reaction temperature of 90 °C might be directly applicable to CHAP samples to determine their formation temperatures.

The Plio-Pleistocene expansion of Eastern Africa savanna ecosystems was a major driver for morphological and behavioral innovations in hominin evolution. Most evidence for hominin ecosystem reconstructions originates from the Eastern Rift in today's Somali-Masai Endemic Zone. We provide stable carbon (δ 13 C) and oxygen (δ 18 O) isotope data from 22 bovid, equid, suid, hippopotamid and elephant teeth from the southern part of the East African Rift and supplement these by δ 18 O values of present-day meteoric water. This region (Karonga Basin, Malawi) hosts remains of Homo rudolfensis and Paranthropus boisei . It is situated between hominin-bearing sites in Eastern and Southern Africa and therefore fills an important geographical gap for hominin evolution. Tooth enamel δ 13 C and δ 18 O data of 14 large-bodied mammalian herbivore species from Units 2 and 3 (ca. 4.3 to 0.6 Ma) in the Chiwondo Beds provide information about foraging strategies and vegetation patterns. Our stable isotope data reflect C 3 -dominated ecosystems that permitted access to open C 4 -environments for migratory mammals. Many analyzed taxa show evidence for mixed diets with high abundances of C 3 -biomass consumption; only selected bovids were specialized grazers. δ 18 O of present-day meteoric water reflects rainfall amount and seasonality, elevation, and lake evaporation. δ 18 O values of Karonga Basin herbivore enamel are generally low and cover values similar to present-day drinking water, indicating both, evaporated and freshwater sources. Comparison of δ 13 C values from the Karonga Basin with other Eastern African herbivore communities reveals significant differences in dietary patterns with much more generalized mixed C 3 /C 4 , and pure C 3 feeding behaviors in the Malawi Rift. Similarly, enamel δ 18 O values are lower than in most Plio-Pleistocene Eastern African herbivores, suggesting more humid conditions. Collectively, our data support models in which early hominin foraging activity included access to C 3 -dominated biomes, complicating traditional interpretations linking early human evolutionary innovations to a shift towards savanna habitats.

Eocene hyperthermals are among the most enigmatic phenomena of Cenozoic climate dynamics. These hyperthermals represent temperature extremes superimposed on an already warm Eocene climate and dramatically affected the marine and terrestrial biosphere, yet our knowledge of temperature and rainfall in continental interiors is still rather limited. We present stable isotope (δ18O) and clumped isotope temperature ( Δ 47 ) records from a middle Eocene (41 to 40 Ma) high-elevation mammal fossil locality in the North American continental interior (Montana, USA). Δ 47 paleotemperatures of soil carbonates delineate a rapid +9/−11 °C temperature excursion in the paleosol record. Δ 47 temperatures progressively increase from 23 °C ± 3 °C to peak temperatures of 32 °C ± 3 °C and subsequently drop by 11 °C. This hyperthermal event in the middle Eocene is accompanied by low δ18O values and reduced pedogenic carbonate concentrations in paleosols. Based on laser ablation U/Pb geochronology of paleosol carbonates in combination with magnetostratigraphy, biostratigraphy, stable isotope, and Δ 47 evidence, we suggest that this pronounced warming event reflects the Middle Eocene Climatic Optimum (MECO) in western North America. The terrestrial expression of northern hemisphere MECO in western North America appears to be characterized by warmer and wetter (sub-humid) conditions, compared to the post-MECO phase. Large and rapid shifts in δ18O values of precipitation and pedogenic CaCO3 contents parallel temperature changes, indicating the profound impact of the MECO on atmospheric circulation and rainfall patterns in the western North American continental interior during this transient warming event.

The eastern equatorial Pacific Ocean (EEP) upwelling system supports >10% of the present-day global ocean primary production, making it an important component in Earth's atmospheric and marine carbon budget. Traditionally, it has been argued that since intensification of Northern Hemisphere glaciation (iNHG, ~2.7 Ma), changes in EEP productivity have predominantly depended on trade wind strength-controlled upwelling intensity. An alternative hypothesis suggests that EEP productivity is primarily controlled by nutrient supply from the high southern latitudes via mode waters. Here we present new high-resolution data for the latest Pliocene/early Pleistocene from Ocean Drilling Program Site 849, located within the equatorial divergence system in the heart of the EEP upwelling regime. We use carbon isotopes in benthic and planktic foraminiferal calcite and sand accumulation rates to investigate glacial-interglacial (G-IG) productivity fluctuations between 2.65 and 2.4 Ma (marine isotope stages (MIS) G1 to 94). This interval includes MIS 100, 98, and 96, three large-amplitude glacials (~1‰ in benthic δ18O) representing the culmination of iNHG. Our results suggest that latest Pliocene/early Pleistocene G-IG productivity changes in the EEP were strongly controlled by nutrient supply from Southern Ocean-sourced mode waters. Our records show a clear G-IG cyclicity from MIS 100 onward with productivity levels increasing from full glacial conditions and peaking at glacial terminations. We conclude that enhanced nutrient delivery from high southern latitudes during full glacial conditions together with superimposed intensified regional upwelling toward glacial terminations strongly regulated primary productivity rates in the EEP from MIS 100 onward.

The topography of the present-day Washington Cascades impacts atmospheric circulation and precipitation patterns in the Pacific Northwest, introducing a pronounced orographic rain shadow in the lee of the mountain range. The temporal development of Cascade topography, however, remains largely unconstrained for the early Cenozoic. Based on coupled carbonate clumped isotope (Δ47) and oxygen isotope (δ18O) measurements we reconstruct δ18O values of Eocene groundwater (δ18Owater) in the Chumstick basin (central Washington), today located in the Cascade rain shadow. Δ47 (paleo)thermometry indicates a systematic change in basin burial temperatures from 110°C to 70°C depending on burial depth in the basin. These data are in good agreement with low-T thermochronological and vitrinite reflectance data, and further constrain the basin burial and exhumation history. In concert with field observations, microstructural analysis, and δ18O values of the analyzed carbonates, we suggest that the Δ47 temperatures and δ18O values reflect open-system carbonate cement recrystallization in meteoric-derived groundwaters during early burial diagenesis. Assuming open-system behavior, reconstructed mean δ18Owater values of ~ −7‰ (middle Eocene) to −9‰ (late Eocene/early Oligocene) are consistent with a low-elevation origin of the corresponding meteoric waters that permeated the sandstone/conglomerate members of the Eocene sedimentary units. In light of the paleogeographic setting of the Chumstick basin, the reconstructed δ18Owater values agree well with Pacific-derived moisture that did not experience strong rainout. The absence of a rain shadow effect therefore permits only moderate Eocene/Oligocene elevations at least for the southern part of the Washington proto-Cascades.

Carbonated hydroxy-apatite (Ca10-b(NH4,K,Na)2b(PO4)6-y[(CO3)2x+(3/2)y(OH)2–2x]; CHAP) was synthesized in batch-type experiments by mixing of calcium (Ca)- and phosphate-bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11° and 65 °C. Compositional changes of the mother solution and solid phase products were followed by powder XRD, scanning-electron microscopy (SEM-EDX), Raman spectroscopy, and elemental analysis. It was found that the transformation at pH values between 7.5 and 7.9 occurs via the dissolution of calcite followed by the precipitation of CHAP. In the mixing approach, crystallization of CHAP took place via precipitation of metastable brushite (CaH(PO4).2H2O) as precursor phase that was further transformed into apatite. Calcium isotope fractionation led to an enrichment of the light isotope by about −0.5 to −1.1‰ in the solid CHAP compared to the aqueous solution, consistently in all experimental approaches, essentially independent of temperature. In some experiments metastable brushite formed prior to transformation to CHAP and 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 recently published experiments.

In this study, we investigated Early Cretaceous (Valanginian, ca. 135 million years ago) climate from subtropical to boreal palaeolatitudes. Combined carbonate clumped isotope and oxygen isotope data derived from sub-arctic, boreal, and sub-tropical fossil belemnite rostra (Mollusca: Cephalopoda) provide new palaeotemperature estimates as well as a constraint on the oxygen isotope composition of seawater. Our belemnite data reveal balmy high-latitude marine temperatures (ca. 22 °C) and warm sub-tropical temperatures (ca. 31 °C). Supplementing our clumped isotope-based temperature estimates with published TEX86 data results in a conservative reconstruction of a latitudinal temperature gradient that is reduced compared to modern conditions. We find that modelling efforts are close to reproducing tropical temperatures when high pCO2 levels are considered. Warm polar temperatures imply, however, that data-model discrepancies remain. Early Cretaceous seawater oxygen isotope values show a modern profile and are much more positive (up to 1.5‰ SMOW) than typically assumed. Based on our findings, if the positive Cretaceous seawater δ18O values are not considered, carbonate δ18O thermometry would underestimate temperatures, most acute at middle and tropical latitudes.

The carbon and nitrogen stable isotopic compositions and elemental characteristics of Pliocene pale and dark lignites in the Jinsuo Basin, Yunnan Province, southwestern China, were investigated. These data were used to develop paleoenvironmental models and to discuss possible geological driving forces for the formation of pale and dark layers. The δ13C values of fossil wood (av. −24.79‰) and fusain samples (av. −24.19‰) are generally higher than the values obtained from bulk pale (av. −27.01‰) and dark (av. −26.38‰) lignite samples. In contrast, the δ15N values of fossil wood (av. −0.63‰) and fusain samples (av. 1.29‰) are lower than the average values of bulk pale lignites (av. 2.17‰) and dark lignites (av. 1.79‰). The difference in the carbon isotopic values between pale and dark lignites can be explained by the very high amount of liptinite and strong degradation of woody material by bacterial activity in pale lignites, which resulted in depletion of 13C in pale lignites, and the wet/humid depositional conditions contributed to the relatively heavy stable carbon isotope compositions of dark layers. The higher δ13C values in the fossil wood and fusain samples can be explained by the general enrichment of 13C in woody material compared to leaves. The weakly negative correlation between the δ15N and δ13C values indicates that, besides bacterial degradation, the liptinite content could also influence the carbon and nitrogen compositions of lignites. The influence of the original plant community (gymnosperms/angiosperms) on the carbon and nitrogen isotopic compositions of bulk lignites is insignificant in the Jinsuo Basin. The paleoenvironmental model suggests deposition of pale layers under relatively dry, cold conditions supporting the expansion of gymnosperms such as Pinus yunnanensis. The slight stepwise uplift of the Tibetan Plateau and the approximate co-occurrence of the more intense Asian monsoon might have supported short periods of a locally dry, cold climate resulting in the lowering of water table which was favorable for the formation of pale layers. The low δ13C values in pale layers further support this. The relatively high SiO2/Al2O3 ratios, higher values of the average detrital/authigenic index, and high levels of TiO2 and Zr in pale layers suggest an increased detrital input relative to dark layers. The dark layers, however, formed in a tropical/subtropical warm, humid climate that favored angiosperm dominance of the vegetation. The long-term geologically stable conditions together with the regionally warm, humid climate resulted in a rise in the water table in the basin, which led to the formation of dark layers until the subsequent slight uplift of the Tibetan Plateau. This conclusion is also supported by the high δ13C values in dark layers and the thickness differences between pale (thin) and dark (thick) layers and the changes in major elements and minerals changes between the two types of layer.

International audience; The fall into the Oligocene icehouse is marked by a steady decline in global temperature with punctuated cooling at the Eocene-Oligocene transition, both of which are well documented in the marine realm. However, the chronology and mechanisms of cooling on land remain unclear. Here, we use clumped isotope thermometry on northeastern Tibetan continental carbonates to reconstruct a detailed Paleogene surface temperature record for the Asian continental interior, and correlate this to an enhanced pollen data set. Our results show two successive dramatic (>9 °C) temperature drops, at 37 Ma and at 33.5 Ma. These large-magnitude decreases in continental temperatures can only be explained by a combination of both regional cooling and shifts of the rainy season to cooler months, which we interpret to reflect a decline of monsoonal intensity. Our results suggest that the response of Asian surface temperatures and monsoonal rainfall to the steady decline of atmospheric CO2 and global temperature through the late Eocene was nonlinear and occurred in two steps separated by a period of climatic instability. Our results support the onset of the Antarctic Circumpolar Current coeval to the Oligocene isotope event 1 (Oi-1) glaciation at 33.5 Ma, reshaping the distribution of surface heat worldwide; however, the origin of the 37 Ma cooling event remains less clear.

A total of 141 samples mostly located in the Coastal Chain and the Sila Massif of Northern Calabria have been collected from 125 different springs and analyzed chemically and for the isotopic ratios 2 H/ 1 H and 18 O/ 16 O of water, with the ultimate aim to investigate isotope–elevation relationships for local meteoric waters. The Small Springs Method (SSM) has been adopted for this purpose. The hydrogeological characteristics of the watersheds of interest indicate that the sampled springs are discharged from water circuits hosted in alluvial and colluvial deposits rather than in the underlying rock substrata. The chemical characteristics of the sampled waters suggest that they are immature and related to shallow and short water circuits, in spite of the variable degree of chemical evolution. The spring waters of relatively high Total Ionic Salinity (TIS >12.5 meq/L) and those from watersheds of comparatively large elevation range (>650 m) and relatively large areas (>17 km 2 ) have been excluded from the analysis of elevation–isotope relationships. An oxygen isotope lapse rate of −0.194 ‰/100 m has been found for the spring water samples of Northern Calabria as a whole, whereas the obtained hydrogen isotope lapse rates are −1.23 ‰/100 m for the Coastal Chain and −1.45 ‰/100 m for the Sila Massif based on measured isotope values and optimized elevation. The following O-isotopes equation is recommended to estimate the average elevation ( H i in m) of the recharge areas of Northern Calabria aquifer systems: δ O 18 = − 0.00194 · H i − 5.91 (1) The maximum estimated uncertainty due to variations in the δ 18 O value over time is 202 m. Use of H isotopes is not recommended for constraining average recharge elevations due to important local variations, reflecting in different relations for the Coastal Chain and the Sila Massif. Assuming that Equation (1) holds true throughout Northern Calabria, an iso-distribution map of the δ 18 O value in rainfall has been drawn for this area.

Sedimentary rocks recording the Toarcian oceanic anoxic event (T-OAE) are marked by a negative carbon isotope excursion (CIE) reaching up to −7‰ and ranking among the largest known in the Phanerozoic. These records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs. Nevertheless, the magnitude of the Toarcian CIE varies significantly from one substrate to another, hence complicating mass balance evaluation of the potential driving mechanisms. Here we show, using high-resolution, paired records of δ13Ctotal organic carbon (TOC) and hydrogen index from the Denkingen core and Dotternhausen quarry (Germany), that the amplitude of the negative CIE in marine organic matter is considerably exaggerated by changes in organic matter sourcing. Our corrected 3–4‰ CIE implies a constant carbon isotope fractionation between organic and carbonate carbon across the T-OAE and may point to a prominent role of cyanobacteria as organic matter producers during the Early Jurassic. These results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pCO2 levels across the T-OAE. Moreover, this corrected 3–4‰ CIE, together with evidence for >5°C seawater warming across the T-OAE, point to the input of >25,000 Gt C with much more 13C-enriched signature than previously modeled. Our results thus allow reconciling inorganic and organic δ13C records of the T-OAE and have important implications for the evaluation of their causal mechanisms.

International audience; Earth's climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma(405)1 to Ma(405)7) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4%) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a similar to 1 Myr period in the late Maastrichtian (67.8-66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change.

The genetic relationship between carbon-bearing species (CO, CO 2 , CH 4 , C 2 H 6 , C 3 H 8 , C 2 H 4 and C 3 H 6 ) was investigated in volcanic-hydrothermal gases emitted from Nisyros (Greece), Vesuvio, La Solfatara (Campi Flegrei) and Pantelleria (all Italy). Apparent carbon isotopic temperatures of the CH 4 –CO 2 system are ~ 360 °C at Nisyros, 420–460 °C at Vesuvio, ~ 450 °C at La Solfatara and ~ 540 °C at Pantelleria. These temperatures are confirmed by measured propene/propane and H 2 /H 2 O concentration ratios. CH 4 and CO 2 equilibrate in the single liquid phase prior to the onset of boiling, whereas propene and propane attain equilibrium in the saturated water vapor phase. Boiling in these high-enthalpy hydrothermal systems might occur isothermally. Once vapor has been extracted from the parental liquid, CO/CO 2 responds most sensitively to the temperature gradient encountered by the ascending gases. Our results imply that the CH 4 –CO 2 isotopic geothermometer can provide reliable information about temperatures of deep hydrothermal liquids associated with volcanism. Propene/propane and H 2 /H 2 O concentration ratios should be measured along with the carbon isotopic composition of CO 2 and CH 4 to provide independent constraints on the geological significance of the apparent carbon isotopic temperatures.

Thermal fluids in Iceland range in temperature from < 10 °C to > 440 °C and are dominated by water (> 97 mol%) with a chloride concentration from < 10 ppm to > 20,000 ppm. The isotope systematics of the fluids reveal many important features of the source(s) and transport properties of volatiles at this divergent plate boundary. Studies spanning over four decades have revealed a large range of values for δD (− 131 to + 3.3‰), tritium (− 0.4 to + 13.8 TU), δ¹⁸O (− 20.8 to + 2.3‰),³He/⁴He (3.1 to 30.4 R[subscript A]), δ¹¹B (− 6.7 to + 25.0‰), δ¹³C[subscript ∑ CO₂](− 27.4 to + 4.6‰), ¹⁴C[subscript ∑ CO₂](+ 0.6 to + 118 pMC), δ¹³C[subscript CH₄](− 52.3 to − 17.8‰), δ¹⁵N (− 10.5 to + 3.0‰), δ³⁴S[subscript ∑ S− II] (− 10.9 to + 3.4‰), δ³⁴S[subscript SO₄](− 2.0 to + 21.2‰) and δ³⁷Cl (− 1.0 to + 2.1‰) in both liquid and vapor phases. Based on this isotopic dataset, the thermal waters originate from meteoric inputs and/or seawater. For other volatiles, degassing of mantle-derived melts contributes to He, CO₂ and possibly also to Cl in the fluids. Water-basalt interaction also contributes to CO₂ and is the major source of H₂S, SO₄, Cl and B in the fluids. Redox reactions additionally influence the composition of the fluids, for example, oxidation of H₂S to SO₄ and reduction of CO₂ to CH₄. Air-water interaction mainly controls N2, Ar and Ne concentrations. The large range of many non-reactive volatile isotope ratios, such as δ³⁷Cl and ³He/⁴He, indicate heterogeneity of the mantle and mantle-derived melts beneath Iceland. In contrast, the large range of many reactive isotopes, such as δ¹³C[subscript ∑ CO₂] and δ³⁴S[subscript ∑ S− II], are heavily affected by processes occurring within the geothermal systems, including fluid-rock interaction, depressurization boiling, and isotopic fractionation between secondary minerals and the aqueous and vapor species. Variations due to these geothermal processes may exceed differences observed among various crust and mantle sources, highlighting the importance and effects of chemical reactions on the isotope systematics of reactive elements. Keywords: Iceland; Isotopes; Thermal fluids; Volatiles

Corals are important marine archives for high-resolution reconstructions of low-latitude climate variability in preinstrumental and historical periods. Herein, we present monthly-resolved records of delta O-18 and Sr/Ca for the 20th century (1917-2007) from a Porites lutea colony from the Maldives (northwestern Indian Ocean). Previous studies of annual mean extension rates of this coral revealed a distinct dependency of coral growth on variations of sea surface temperature (SST) and hydraulic energy, driven by El Nino-Southern Oscillation (ENSO) and southwestern Indian monsoon forcing. This enables the investigation of coral delta O-18 and Sr/Ca ratios from the Maldives as archives of historical ENSO and Indian monsoon variability. Unlike other locations in the Indian Ocean, correlation of delta O-18 and SST is weak (r = -0.42; p < 0.001), suggesting interferences of SST and seawater delta O-18 at the location. These interferences probably caused significantly weaker interannual ENSO signatures in delta O-18 as evident in the extension rates of our coral and in geochemical proxies measured at other sites in the northwestern Indian Ocean. Sr/Ca ratios show bias by nontemperature effects, and were not used to estimate seawater delta O-18 and salinity. Strong decadal variability (10-14 years) in delta O-18, indicative of a Pacific ENSO signal, is not found in instrumental SST, and could be explained by variations in salinity. Interannual and decadal monsoon variability (6-7 yrs and 18-19 yrs), found in the extension rates, was not found in delta O-18, suggesting, in agreement with other studies, that geochemical coral proxy records from the northwestern Indian Ocean do not capture temporal variations of the Indian monsoon strength.

The Domuyo volcanic complex (Neuquén Province, Argentina) hosts one of the most promising geothermal systems of Patagonia, giving rise to thermal manifestations discharging hot and Cl−-rich fluids. This study reports a complete geochemical dataset of gas and water samples collected in three years (2013, 2014 and 2015) from the main fluid discharges of this area. The chemical and isotopic composition (δD-H2O and δ18O-H2O) of waters indicates that rainwater and snow melting are the primary recharge of a hydrothermal reservoir located at relative shallow depth (400–600 m) possibly connected to a second deeper (2–3 km) reservoir. Reactive magmatic gases are completely scrubbed by the hydrothermal aquifer(s), whereas interaction of meteoric waters at the surface causes a significant air contamination and dilution of the fluid discharges located along the creeks at the foothill of the Cerro Domuyo edifice. Thermal discharges located at relatively high altitude (~ 3150 m a.s.l.), namely Bramadora, are less affected by this process, as also shown by their relatively high R/Ra values (up to 6.91) pointing to the occurrence of an actively degassing magma batch located at an unknown depth. Gas and solute geothermometry suggests equilibrium temperatures up to 220–240 °C likely referred to the shallower hydrothermal reservoir. These results, confirming the promising indications of the preliminary surveys carried out in the 1980′s, provide useful information for a reliable estimation of the geothermal potential of this extinct volcanic system, although a detailed geophysical measurements is required for the correct estimation of depth and dimensions of the fluid reservoir(s). Fil: Tassi, F.. Consiglio Nazionale delle Ricerche; Italia. Università degli Studi di Firenze; Italia Fil: Liccioli, Caterina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Ciencias Geológicas. Grupo de Estudio y Seguimiento de Volcanes Activos; Argentina Fil: Agusto, Mariano Roberto. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Chiodini, Giovanni. Istituto Nazionale Di Geofisica E Vulcanologia; Italia Fil: Vaselli, O.. Università degli Studi di Firenze; Italia Fil: Calabrese, S.. Istituto Nazionale Di Geofisica E Vulcanologia; Italia Fil: Pecoraino, G.. Università degli Studi di Firenze; Italia Fil: Tempesti, L.. Università degli Studi di Firenze; Italia Fil: Caponio, Cecilia. Istituto Nazionale Di Geofisica E Vulcanologia; Italia Fil: Fiebig, J.. Università degli Studi di Firenze; Italia Fil: Caliro, S.. Università degli Studi di Firenze; Italia Fil: Caselli, Alberto Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina

Earth’s climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Site U1403, providing an expanded deep ocean record from the North Atlantic (IODP Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role on depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma4051 to Ma4057) and spans 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4 ‰), typical for open ocean settings, are compared to the hemipelagic Zumaia section (N-Spain), with a well-established independent cyclostratigraphic framework. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both records, patterns diverge around 67.5 Ma, with Site U1403 more reliably reflecting global climate change. Our new carbon isotope record and the established cyclostratigraphy from Site U1403 may serve as a future reference for detailed studies of late Maastrichtian events in the North Atlantic.

We celebrate the contribution of Jochen Hoefs to the development of stable isotope (bio)geochemistry on the occasion of his 75th birthday.

In order to constrain spatial variability in watermass conditions within the European Epicontinental Seaway prior to, during and after the Toarcian Oceanic Anoxic Event, carbon (δ13Cbel, δ13Ccarb) and oxygen (δ18Obel, δ18Ocarb) isotope records were obtained from three sections in the Grands Causses Basin (southern France). These data were then compared with similar records along a north–south transect across the European Epicontinental Seaway. As the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes, an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite. Intra-rostral carbon and oxygen-isotope data from six belemnite specimens belonging to the genus Passaloteuthis were collected. Intra-rostral carbon-isotopes are influenced by vital effects, whereas oxygen-isotopes reflect relative changes in temperature and salinity. Palaeotemperatures calculated from δ18Obel-isotope records from the Grands Causses Basin confirm relatively low temperatures throughout the Late Pliensbachian. Similar cool water conditions have previously been shown in Germany, England, Spain and Portugal. A temperature increase of up to 6 °C is observed across the Pliensbachian–Toarcian boundary. A pronounced negative shift of at least −3‰ (Vienna-Pee Dee Belemnite) is recorded in bulk carbonate carbon during the lower Harpoceras serpentinum zone, typical of the Toarcian Oceanic Anoxic Event. Before and after the Toarcian Oceanic Anoxic Event, a good correlation between δ13Ccarb and δ13Cbel exists, indicating well-ventilated bottom-waters and normal marine conditions. Instead, data for the Toarcian Oceanic Anoxic Event indicate the development of a strong north–south gradient in salinity stratification and surface-water productivity for the Western Tethyan realm. This study thus lends further support to a pronounced regional overprint on carbon and oxygen-isotope records in epicontinental seaways.

We have addressed the origins of methane in fumarolic, thermal and cold emissions discharging from a diversity of geological settings spread all over the Italian Peninsula and at Panarea and Pantelleria islands. Fluid discharges from the main geothermal systems of the peri-Tyrrhenian area (including Mt. Amiata, Larderello, Latera and Manziana) show δ13C-CH4 and δD-CH4 values >−28‰ V-PDB and >−160‰ V-SMOW, respectively, and C1/C2 + concentration ratios > 1000. These patterns suggest that CH4 discharged from these systems is primarily generated by abiogenic reduction of CO2 and/or CO. Methane seems to have, at least partially, a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or, alternatively, to methane polymerization. Fumaroles from the volcanic systems of Solfatara, Vesuvio, Panarea and Pantelleria have C1/C2 + concentration ratios in a wide range (from 17 to 4300), but δ13C-CH4 and δD-CH4 values >−21‰ V-PDB and >−120‰ V-SMOW, respectively. Such isotopic values are very similar to those reported for CH4 discharging from ultramafic hydrothermal systems. In agreement with recent evidence provided for Solfatara and Pantelleria we, therefore, infer that the CH4 in the volcanic fumaroles is mainly abiogenic, too. The δ13C-CH4 (from − 21.6 to − 36.9‰ V-PDB) and δD-CH4 (from − 113 to − 164‰ V-SMOW) values, as well as the C1/C2 + concentration ratios (from 19 to 2240), in the CO2-rich fluid discharges located between the geothermal-volcanic systems and the Apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish, suggesting that the CH4 production is mainly related to thermogenic processes. According to this general trend, the CH4-dominated fluids from mud volcanoes located eastwards of the CO2-rich emissions are fed by an almost pure thermogenic source. The easternmost fluid discharges from the Po valley and the Adriatic coast, where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient, record the lowest δ13C-CH4 and δD-CH4 values, i.e. as low as − 69‰ V-PDB and

Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.

International audience; Mg/Ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography. However, our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite Mg/Ca is limited. Here we report results of a study designed to shed new light on ecological, size-related and very early (water column) diagenetic controls on Mg/Ca in planktic foraminiferal calcite. We analysed Mg/Ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 μm-window sieve fractions in a core-top sample from the North Atlantic Ocean. We also analysed Mg/Ca in four of these nine species from plankton-tow samples collected from 0 to 2500 m water depth in the North Atlantic Ocean and Arabian Sea. Our core-top study confirms that sensitivity of Mg/Ca to change in test size is species-specific but reveals an overall decrease in Mg/Ca with increasing test size in all but one species, Orbulina universa, for which Mg/Ca increases with size. These findings are broadly consistent with known ecological behaviour suggesting that the size-related signal is largely environmentally rather than calcification-rate controlled. Our results underscore the need to undertake Mg/Ca palaeothermometry on narrow size fractions of planktic foraminifers, particularly for shallow-dwelling species such as G. bulloides and G. ruber where Mg/Ca is most sensitive to test size across the size range of 200–350 μm. Our plankton-tow data from the Arabian Sea are in agreement with in-situ temperatures. In contrast, our data from the North Atlantic Ocean reveal large variability and marked offsets (to warmer values) from in-situ temperatures that are interpreted to reflect lateral advection from the south, storm-induced vertical mixing of the water column and/or the influence of surface-water salinity on the Mg/Ca signal. None of our plankton-tow Mg/Ca data shows any evidence of test dissolution in the water column. Our study provides important verification that the Mg/Ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor, thereby satisfying an important precondition of its palaeo-proxy utility.

We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ 13 C TOC and δ 15 N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ 13 C DIC were used to trace OM decomposition. The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH 4 and CO 2 in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO 3 . The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.

Tubular carbonate concretions of up to 1 m in length and perpendicular to bedding, occur abundantly in the Upper Pliensbachian (upper Amaltheus margaritatus Zone, Gibbosus Subzone) in outcrops (Fontaneilles section) in the vicinity of Rivière-sûr-Tarn, southern France. Stable isotope analyses of these concretions show negative δ13C values that decrease from the rim to the center from −18.8‰ to −25.7‰ (V-PDB), but normal marine δ18O values (−1.8‰). Carbon isotope analyses of Late Pliensbachian bulk carbonate (matrix) samples from the Fontaneilles section show clearly decreasing C-isotope values across the A. margaritatus Zone, from +1‰ to −3‰ (V-PDB). Isotope analyses of coeval belemnite rostra do not document such a negative C-isotope trend with values remaining stable around +2‰ (V-PDB). Computer tomographic (CT) scanning of the tubular concretions show multiple canals that are lined or filled entirely with pyrite. Previously, the formation of these concretions with one, two, or more central tubes, has been ascribed to the activity of an enigmatic organism, possibly with annelid or arthropod affinities, known asTisoa siphonalis. Our results suggest tisoan structures are abiogenic. Based on our geochemical analyses and sedimentological observations we suggest that these concretions formed as a combination of the anaerobic oxidation of methane (AOM) and sulfate reduction within the sediment. Fluids rich in methane and/or hydrocarbons likely altered local bulk rock carbon isotope records, but did not affect the global carbon cycle. Interestingly, Tisoa siphonalis has been described from many locations in the Grands Causses Basin in southern France, and from northern France and Luxemburg, always occurring at the same stratigraphic level. Upper Pliensbachian authigenic carbonates thus possibly cover an area of many thousand square kilometers. Greatly reduced sedimentation rates are needed to explain the stabilization of the sulfate-methane transition zone in the sedimentary column in order for the tubular concretions to form. Late Pliensbachian cooling, reducing run-off, and/or the influx of colder water and more vigorous circulation could be responsible for a halt in sedimentation. At the same time (thermogenic) methane may have destabilized during a major phase of Late Pliensbachian sea level fall. As such Tisoa siphonalis is more than a geological curiosity, and its further study could prove pivotal in understanding Early Jurassic paleoenvironmental change.

Chemical and isotopic analyses of the main gas manifestations of the island of Pantelleria (Italy) were used to gain insight on the origin of the released methane. Results indicate that the most probable origin is through abiogenic reactions within the hydrothermal system. Methane and CO 2 flux measurements from the soils were made with the accumulation chamber method in an area of about 0.015 km 2 within the main fumarolic area of the island (Favara Grande). The 23 measurements range from − 34 to 3550 mg m −2 d − 1 for CH 4 and from 0.6 to 379 g m − 2 d − 1 for CO 2 . The relationships between CH 4 and CO 2 fluxes and the CH 4 /CO 2 ratios in the gases collected between the depths of 25 and 100 cm provide evidence for methanotrophic processes within the soils. Methane output for the surveyed area was calculated to be 2.5 t a − 1 and extrapolated to about 5–10 t a − 1 for the entire volcanic/hydrothermal system of the island. Previous higher estimates of the CH 4 output at Pantelleria (Etiope et al., 2007, J. Volcanol. Geotherm. Res., 165, 76–86) were based on soil CO 2 output and CH 4 /CO 2 ratios in fumarolic gases; the present work provides the first direct CH 4 flux data and it suggests that methanotrophic activity in the soil could be substantial in reducing the CH 4 emission to the atmosphere.

One of the five largest mass extinctions of the past 600 million years occurred at the boundary of the Triassic and Jurassic periods, 201.6 million years ago. The loss of marine biodiversity at the time has been linked to extreme greenhouse warming, triggered by the release of carbon dioxide from flood basalt volcanism in the central Atlantic Ocean. In contrast, the biotic turnover in terrestrial ecosystems is not well understood, and cannot be readily reconciled with the effects of massive volcanism. Here we present pollen, spore and geochemical analyses across the Triassic/Jurassic boundary from three drill cores from Germany and Sweden. We show that gymnosperm forests in northwest Europe were transiently replaced by fern and fern-associated vegetation, a pioneer assemblage commonly found in disturbed ecosystems. The Triassic/Jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons, which, in the absence of charcoal peaks, we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava. We conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone. Instead, we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction.

Thermogenic hydrocarbons entirely deriving from the thermal degradation of organic matter usually exhibit methane to ethane plus propane ratios smaller than 100. We present hydrocarbon distribution data of continental hydrothermal gases, whose methane has been independently identified to derive from the abiogenic reduction of CO2. We find that excess amounts of methane with respect to thermogenic hydrocarbon distributions are characteristic for the investigated gases. A similar pattern is observed for well discharges whose temperatures are too high to support any microbially mediated methanogenesis. These findings strongly suggest that abiogenic methane production in continental-hydrothermal systems is a more widespread process than previously assumed. The maximum contribution of such emissions to the modern atmospheric CH4 budget is estimated at ~1%.