Stable Oxygen Isotope Analyses Research Articles

Stable isotope and hydrogeological measurements: Implications for transit time and mixing ratio in a riparian system of the Danube River

Riverbank filtration has a very important role in the supply of drinking water globally. However, this water source is vulnerable, because rivers are easily contaminated. To assess its vulnerability, it is essential to understand the properties of the aquifer including the sources of the water and the transit time. Therefore, a comprehensive investigation of the Hungarian Danube River-riverbank system was conducted on two of its islands (Szentendre and Csepel). Water level, temperature and electrical conductivity were monitored in the wells located in the riverbank, and water samples were collected regularly from the wells and the river for stable hydrogen and oxygen isotope analyses over a year. It was found that the wells located at different distances from the Danube River have various responses to the hydrological changes occurring in the river. Transit time distributions (TTD) belonging to different production wells were determined by the lumped parameter method, based on the convolution integral. Differences in the TTDs of the wells are explained by their distance from the Danube River, spatial variations in the aquifer hydraulic properties and the varying pumping rates. Additionally, the estimated mixing ratio of different water sources (i.e., Danube River and background shallow groundwater infiltrated from precipitation) to the exploited water suggests that the contribution of precipitation is less than 20 %.Furthermore, the stable water isotope data of the Danube River in the Budapest area was measured from 1998 to 2021 was gathered and evaluated. It appears that the δ18O values of the Danube River at Budapest show systematically higher values than those from Vienna, indicating lowland water contribution and some evaporation effect.

A dual bivalve approach for interpreting past sea surface temperatures and seasonality from shell midden sites using oxygen isotope sclerochronology

Stable oxygen isotope (δ18O) analysis of archaeological shellfish remains combined with sclerochronology can be used to precisely reconstruct past sea surface temperature (pSST), season(s) of shellfish collection, and thus the season(s) of archaeological site occupation. Our study tests if δ18Oshell and sclerochronological analyses of marine bivalve species Leukoma staminea – with previously unassessed seasonality and pSST potential – can provide additional insights not captured by the better studied species, Saxidmous gigantea in British Columbia (BC, Canada). We analyzed live-collected L. staminea and S. gigantea shells from Sechelt, BC, and compared results to archaeological shell data from Powell River, BC, in the territory of the Tla'amin First Nation (1065 to 797 cal. B.P.). The seasonality of shellfish harvest differed between species, with S. gigantea preferentially collected in the spring, whereas L. staminea collected year-round. This highlights that sole-species seasonality studies may miss important variability harvesting strategies. Additionally, comparisons between instrumental (5.7 to 20.4 °C) and reconstructed SST from modern L. staminea δ18Oshell (5.6 to 18.4 °C) showed good agreement in annual range. Our results indicate that archaeological S. gigantea record a wider range of pSST (−1.6 to 22.9 °C) than archaeological L. staminea (5.8 to 25.9 °C), suggesting that S. gigantea may be a more sensitive palaeotemperature recorder. Further, we found that using the same reconstructed δ18Owater value for both species in pSST reconstruction caused an overestimation of temperature. Accordingly, we argue that it is critical to calibrate the equation with corresponding species-specific δ18Oshell values, regardless of both having aragonite mineral structures. Our study highlights the potential of L. staminea to broaden seasonality interpretations while clarifying that its use for pSST reconstruction may not capture the lower range of temperature.

Multistage selective diagenesis increasing poro-perm properties of Anisian sponge-microbial-coral patch reefs and adjacent facies in the Muschelkalk of Upper Silesia, Southern Poland

Carbonate rocks, particularly reefs and circum-reef facies, are significant reservoir rocks whose reservoir properties depend on their primary composition and diagenetic history. This paper reconstructs the influence of multistage selective diagenesis on the pore system evolution and porosity-permeability properties of the Anisian tropical reef system (Karchowice and Diplopora Beds) in the Muschelkalk of Upper Silesia, southern Poland, using field and slab observations, standard and cathodoluminescence petrography, bulk and SIMS carbon and oxygen stable isotope analyses, porosity-permeability plug study, and computer image analysis of macroporosity (>5 mm across). The reef system comprises two distinct levels of sponge-microbial(-coral) reef mounds surrounded by diverse bioclastic, peloidal, coated-grain, and micritic facies rich in Balanoglossites burrows. The strata experienced complex diagenetic alterations related to various fluids (marine, evaporitic, meteoric) and diagenetic environments (shallow substratal, burial, telogenetic), including (in chronological order): 1) early-marine precipitation of isopachous fibrous rims; 2) early dissolution during emersion; 3) brine-reflux dolomitization; 4) patchy silicification; 5) recrystallization; 6) burial calcite cementation by heated marine fluid; 7) deposition of vadose silt; 8) meteoric calcite cementation; 9) chemical compaction; 10) fracturing; and 11) final karstification, dedolomitization, FeO precipitation, and Liesegang ring formation by meteoric water during Cenozoic telogenesis. Many processes were selective and affected the same (more permeable) parts of the rocks. The strata exhibit porosities reaching 50% (combined plug porosity of 6–35% and macroporosity of up to 20%) and plug permeabilities of 0.07–70 mD, with the highest values occurring in the reefs and burrowed facies. The dominant late-stage telogenic dissolution pores originated from selective removal of dolomitized micrite within burrows and between sponge-microbial automicrite as well as dolomite crystals. The study illustrates the transition of the reef system from tight to porous due to multistage selective diagenesis and fluid flow, which enhanced subtle permeability differences between various types of micrite. This is the first case where four different fluids (dolomitizing, early dissolving, calcite-forming, and late dissolving) selectively migrated through the same rock parts at different times and modified them one after another.

Lithofacies and diagenetic controls on thrombolitic dolomite reservoir development from the Precambrian Dengying Formation in the central Sichuan Basin, SW China

Microbialite reservoirs are of great importance in oil and gas exploration. However, there is still a lack of comprehensive studies on the formation mechanisms of thrombolitic reservoirs, a specific type of microbialite. This research focuses on the oldest thrombolitic dolomite reservoir located within the Precambrian Dengying Formation in the central Sichuan Basin, southwestern China. A multi-disciplinary approach was employed to characterize different thrombolite facies and elucidate the formation mechanism of thrombolitic dolomite reservoirs and their controlling factors, involving core observation, thin-section analysis, cathodoluminescence, scanning electron microscope (SEM) microscopy, elemental analysis using LA-ICP-MS, and carbon and oxygen stable isotope analysis. Based on variations in texture, four types of thrombolite were identified: 1) distinct clotted thrombolite, 2) diffuse and regular clotted thrombolite, 3) diffuse and irregular clotted thrombolite, and 4) composite clotted thrombolite. Notably, the diffuse clotted thrombolitic dolomite is the prevalent lithology in the reservoir. Through modification by meteoric water, organic acid fluids, and hydrothermal fluids, a reservoir with dominant porosity in the form of primary growth-framework pores, dissolution pores, and vugs was formed. This resulted in the development of two high-quality reservoir intervals within the Second Member and at the top of the Fourth Member of the Dengying Formation. The growth-framework porosity of the thrombolites, epigenetic karstification, and tectonic fracturing were mainly conducive to reservoir development. However, various types of cementation have reduced porosity and connectivity within the reservoir. Overall, this study is a valuable example of the methodology required to understand meso- and microstructures of deep-buried thrombolitic dolomite reservoirs, including their heterogeneities and diagenesis, as the original structures influence diagenesis.

Stable oxygen isotopes reveal different thermal regimes during the Early Pliocene in the southern North Sea Basin: a multi-species approach

ABSTRACT Oxygen stable isotope (δ18O) analysis of marine biogenic carbonates is widely used to study the temperature at which the hard parts precipitated. This technique enables investigation of the environmental conditions experienced by carbonate-shelled organisms throughout their life. We used this approach on four bivalve species from the Coralline Crag Formation (Early Pliocene; UK), where warm- and cold-associated species co-occur in the Ramsholt Member. Our results reveal species-specific differences in reconstructed temperature. Two distinct climatic settings were identified: a cold setting with seafloor temperatures of 7.3 °C in winter and 12.4 °C in summer, and a warm one with seafloor temperatures of 10.4 °C in winter to above 14 °C in summer. These absolute temperatures were calculated using a modelled value of seawater δ18O (+0.1‰) that is open to question, but the disparity in temperatures exists whatever value is used. Interestingly, the reconstructed temperatures for some of the studied species align with those of their modern relatives: Arctica islandica records the coldest temperatures in this dataset, while Centrocardita squamulosa ampla indicates warmer conditions. Aequipecten opercularis, a eurythermal pectinid, exhibited the broadest range of temperatures. The interval during which the Coralline Crag was deposited (c. 4.4‒3.8 Ma) is generally regarded as relatively warm. However, the presence of A. islandica and the absolute seawater temperatures derived from shell δ18O suggest the occurrence of sufficiently long cool periods for the establishment and survival of this long-lived species. Data from specimens of C. squamulosa ampla and A. islandica collected from a single bed point to glacial/interglacial-type climate fluctuation. These results confirm that the presence of A. islandica is a marker for cold temperate environments. These results also confirm that assemblage information is not sufficient to determine palaeoclimatic conditions, and that reconstructed temperatures from shell δ18O can reveal time-averaging in fossil shell beds.

Micritisation products in the inner ramp settings of the Abu Dhabi Lagoon

AbstractIn numerous carbonate reservoirs in the Middle East, peloidal packstone‐grainstones are rock types with excellent pore storage potential in micritised microporous grains. However, the origin of the micro‐porosity and associated micro‐spar remains unclear, and one hypothesis is that both micro‐spar and porosity originate from early marine micritisation and were later altered during subsequent diagenesis (i.e. cementation recrystallisation). The south‐eastern coast of the Arabian Gulf is recognised as a modern, albeit miniature, depositional setting analogue to Mesozoic carbonate sequences that form the supergiant reservoirs of the Middle East. Using optical microscopy, backscattered scanning electron microscopy and carbon and oxygen stable isotope analysis the present study aims to document the nature of internal microstructures of micritic envelopes and peloids from the surface sediments of various sub‐environments of the Abu Dhabi Lagoon. Results highlight a high degree of diversity and heterogeneities of most micritic envelopes and peloids observed across the sub‐environments. First, carbonate grains from ooid and bioclastic shoals show the simpler micritic envelopes. Here, micritic envelopes and peloids show sparse microborings filled with banded radial aragonite cement, a pattern of production of cryptocrystalline texture (e.g. micritisation) that is similar to the sequence of micritisation observed in the modern sediment of the Great Bahama Bank. Conversely, in the subtidal and intertidal zones with mangroves or seagrass, the micritic envelopes and peloids are much more complex and show multiple generations of microborings that are either empty or filled with carbonate materials of varying types (i.e. various cements, fragments, etc.).

Sample preservation methods for nitrous oxide concentration and isotope ratio measurements in aquatic environments

AbstractThe nitrogen (N) and oxygen (O) stable isotope analysis of dissolved nitrous oxide (N2O) can provide important constraints on the sources and cycling of N2O in aquatic environments. The isotopic composition of aqueous N2O, both in field (natural abundance) or experimental (15N‐labeling) samples, however, may be altered by abiotic reactions involving nitrite () or hydroxylamine (NH2OH) and microbial activity during sample storage, if samples are not adequately preserved. Here we tested five different preservatives, mercuric chloride (HgCl2), copper sulfate (CuSO4), zinc chloride (ZnCl2), hydrochloric acid (HCl) mixed with sulfamic acid (SFA), and sodium hydroxide (NaOH), for fixing natural water samples from an estuary and a lake with different concentrations over a range of different storage times for N2O analyses. ZnCl2 and CuSO4 decreased the pH, and led to abiotic N2O production from , shifting the N2O isotopic composition significantly. Removal of with a mixture of SFA and HCl did not always prevent the alteration of the original N and O isotope composition of N2O, confirming the requirement for complete removal, and underscoring the biasing effects of at very low pH, even at trace levels. At low background, HgCl2 preservation led to robust and accurate results. However, in light of its toxicity and bioaccumulation potential in food webs, this fixative should be avoided. The addition of NaOH reduced abiotic side reactions involving , and yielded the most reliable and reproducible results for N2O concentration and isotope ratio measurements across tested settings and storage times.

Differences in the intensity of past forest fire events inferred from stable oxygen isotope analysis of charred bark

Understanding past fire regimes requires reliable proxy data that record fire conditions and preserve them over time. The objective of this study was to determine if the oxygen isotope composition of charred bark samples (pyrogenic organic matter) could be used as proxy data to differentiate wildfires based on burn intensity. We collected charred and uncharred bark samples from three fire sites in northern Ontario, Canada that represented a gradient of fire intensity as depicted by Fire Weather Index (FWI) data. We hypothesized that the mean Δ18Obark-char (the difference between δ18O of uncharred bark and a charred sample) would be greater for fires with higher intensities. Analysis of variance of Δ18Obark-char indicated a significant effect of fire event ( F = 73.6, p < 0.001), which explained 57.0% of the variance. A prescribed surface fire treatment (mean FWI = 9.5) had significantly lower Δ18Obark-char than two natural crown fires (FWI = 21 and 27). These results demonstrate that Δ18Obark-char differentiated moderate from high intensity fires in a similar manner to the FWI data.

Clumped and in situ carbon and oxygen isotopes of calcite as tracers for oxidation of hydrocarbons in deep siliciclastic strata

Abstract The oxidation of hydrocarbons, including methane, is part of interrelated hydrogeochemical reactions affecting the carbon budget in Earth’s crust. To investigate these processes in deep siliciclastic strata, we analyzed core samples from Lower Triassic red beds in the Mahu Sag (Junggar Basin, northwest China) by coupling petrological observations with high-resolution in situ secondary ion mass spectroscopy stable carbon and oxygen isotope analyses and clumped isotopes (Δ47) of authigenic calcite. The strata contain variable oil and gas content as well as abundant high-valence Fe and/or Mn oxides. Three sequential generations of cement occur, which are characterized as (1) non-luminescent, early diagenetic calcite (MnO <0.3%, δ13CVPDB [Vienna Peedee belemnite] = −5.6‰ to −4.1‰); (2) bright-orange luminescent late-stage I calcite (0.75%–5.23% MnO, δ13C = −51.4‰ to −25.8‰); and (3) dull-orange late-stage II calcite (4.10%–12.93% MnO, δ13C = −91.4‰ to −30.9‰). Clumped isotopic thermometry reveals that the calcite precipitation temperature increases successively from <40 °C, to 81–107 °C, to finally 107–132 °C, corresponding to three precipitation time periods: before the Late Triassic, from the Early Jurassic to the Early Cretaceous, and from the Early Cretaceous to the present, respectively. δ13C values of −55.7‰ to −25.8‰ indicate that late-stage I calcite is the final product of oxidation of both methane and C2+ hydrocarbons, whereas δ13C values as low as −91‰ indicate that late-stage II calcite is mainly derived from the thermochemical oxidation of methane (δ13C = −46.8‰ to −39.3‰) induced by high-valence Mn and/or Fe oxides. For late-stage I calcite, hydrocarbon oxidation was most likely promoted by high temperatures, although microbial oxidation cannot be completely ruled out. The higher precipitation temperature of late-stage II calcite demonstrates that the oxidation of methane requires higher activation energies than oxidation of C2+ hydrocarbons. We provide reliable geochemical evidence for thermally induced sequential oxidation of hydrocarbons within deep siliciclastic strata.

When the woolly rhinoceroses roamed East Asia: a review of isotopic paleoecology of the genus Coelodonta from the Tibetan Plateau to northern Eurasia

East Asia, being the evolutionary center of Coelodonta, offers a unique opportunity to explore the spatiotemporal paleoecologies of this genus. This study utilized bulk and serial stable carbon and oxygen isotope analyses on the Coelodonta nihowanensis and other ungulates from the Longdan fauna as well as two modern goats in the Linxia Basin, aiming to explore the paleoecology of C. nihowanensis at the periphery of the Tibetan Plateau during the Early Pleistocene. The isotopic results of these mammals indicated that C3 vegetation was possibly a major component of the local environment in the Linxia Basin, which was influenced by a seasonal summer monsoon. C. nihowanensis specimens in the Longdan fauna were possibly mixed feeders, as indicated by the wide distribution of their δ13C values and the intermediate δ18O values compared to other coexisting ungulates. Moreover, the comparison of the δ13C and δ18O values of similar taxa from the Linxia and Nihewan basins has revealed spatiotemporal differences in the paleoclimate and paleoenvironments of these two regions throughout the Early Pleistocene. This provides a holistic framework for understanding the paleoecology of the C. nihowanensis. The isotopic results of the C. nihowanensis in the Linxia and Nihewan basins suggested varied foraging ecologies across different sites and time spans during the Early Pleistocene. This underscores the adaptability of the C. nihowanensis to diverse environments from west to east in northern China. By scrutinizing the evolutionary ecological history of the woolly rhinoceroses from its ancestor, Coelodonta thibetana, to its final form, Coelodonta antiquitatis, this study sheds light on the ecological adaptation of this genus from the Pliocene to Late Pleistocene, spanning its migration from the Tibetan Plateau to northern Eurasia.

Shallow-water temperature seasonality in the middle Cretaceous mid-latitude northwestern Pacific

Temperature seasonality during the middle Cretaceous provides vital information about climate dynamics and ecological traits of organisms under the conditions of the “supergreenhouse” Earth. However, sub-annual scale paleotemperature records in the mid-latitude region remain limited. In this study, sclerochronological and stable oxygen isotope (δ18O) analyses of bivalve fossils from the northwestern Pacific (paleolatitude: 44°N) were used to estimate their life history and sub-annual scale temperature patterns of the middle Cretaceous. The materials studied included Cucullaea (Idonearca) delicatostriata and Aphrodina pseudoplana recovered from middle Turonian (middle Cretaceous) shallow marine deposits in Hokkaido, northern Japan. Growth increment width and shell δ18O of C. (I.) delicatostriata revealed that the growth rate was temporally maximized and then minimized, which can be interpreted as representing spring and winter growth, respectively. Approximately 25 fortnightly growth increments occurred within that cycle, suggesting that shell formation proceeded continuously throughout the year. Based on shell δ18O values, shallow-water temperatures from 28°C to 35°C with 7°C seasonality were estimated, under the assumption that seawater δ18O values were annually invariant at −1‰ relative to VSMOW. This temperature seasonality in the middle Cretaceous is more than 5°C smaller than the seasonality of modern shallow-water environments at the same latitudes. These findings, taken together with previous studies of other oceanic regions, suggest that the Northern Hemisphere had low seasonal shallow-water temperature variation of up to 10°C in the middle Cretaceous.

Multiproxy evidence for environmental stability in the Lesser Caucasus during the Late Pleistocene

The Lesser Caucasus, situated between Asia and Europe, has long been recognised as a key region for the study of human evolution in terms of the timing and routes of dispersal, as well as, ecological adaptations. In particular, scholars have argued whether stable environments persisted in the region throughout the last glaciation, serving as a refugium for temperate biota, likely attracting human settlement and use. Here, we present the results of a multidisciplinary study of Karin Tak Cave, which contains sediments that accumulated between 48,000 and 24,000 cal yr BP. We examined biostratigraphic changes at the site by looking at the composition of fauna, which we hypothesise to be naturally accumulated, in different stratigraphic phases using traditional zooarchaeological approaches combined with collagen fingerprinting (ZooMS, Zooarchaeology by Mass Spectrometry). To gain further insights into regional palaeoenvironmental conditions, we also applied stable carbon and oxygen isotope analyses to faunal tooth enamel. The obtained results suggest that the onset of the last glaciation did not cause dramatic changes in regional environments, indicating that the Lesser Caucasus was a climatically and ecologically stable region despite significant global climatic changes during this period.

Method to measure tree-ring width, density, elemental composition, and stable carbon and oxygen isotopes using one sample

Tree-ring width (RW), density, elemental composition, and stable carbon and oxygen isotope (δ13C, δ18O) are widely used as proxies to assess climate change, ecology, and environmental pollution; however, a specific pretreatment has been needed for each proxy. Here, we developed a method by which each proxy can be measured in the same sample. First, the sample is polished for ring width measurement. After obtaining the ring width data, the sample is cut to form a 1-mm-thick wood plate. The sample is then mounted in a vertical sample holder, and gradually scanned by an X-ray beam. Simultaneously, the count rates of the fluorescent photons of elements (for chemical characterization) and a radiographic grayscale image (for wood density) are obtained, i.e. the density and the element content are obtained. Then, cellulose is isolated from the 1-mm wood plate by removal of lignin, and hemicellulose. After producing this cellulose plate, cellulose subsamples are separated by knife under the microscope for inter-annual and intra-annual stable carbon and oxygen isotope (δ13C, δ18O) analysis. Based on this method, RW, density, elemental composition, δ13C, and δ18O can be measured from the same sample, which reduces sample amount and treatment time, and is helpful for multi-proxy comparison and combination research.

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Hydraulic Relationship between Hulun Lake and Cretaceous Confined Aquifer Using Hydrochemistry and Isotopic Data

Marine resource exploitation and human settlement patterns during the Neolithic in SW Europe: stable oxygen isotope analyses (δ18O) on Phorcus lineatus (da Costa, 1778) from Campo de Hockey (San Fernando, Cádiz, Spain)

In recent decades, investigations in the southern Iberian Peninsula have increased our understanding of the socio-economic impact of the spread of the Neolithic in southwestern Europe, including changes in marine resources exploitation. Nevertheless, considerable uncertainty still exists around the seasonality of such subsistence systems and the putative role of marine fish and shellfish to the evolving agro-pastoral economies. Earlier studies on the European Atlantic coast (including Iberia) have shown that the stable oxygen isotope (δ18O) values from the topshell Phorcus lineatus (da Costa, 1778) can be reliably used to derive seasonal sea surface temperatures (SST) during its lifespan. This information can be used by archaeologists to estimate the seasonality of mollusc collection in the past, and to shed light into settlement and subsistence patterns. This paper presents the results of a stable isotope study on archaeological shells of P. lineatus recovered from the Neolithic settlement of Campo de Hockey (Cádiz, Spain). We analysed shells from both funerary and residential contexts and found that P. lineatus was consumed year-round, but with a stronger preference during winter. Our results therefore contribute to advance our understanding of the role of coastal environments in early farming societies of southwestern Europe.

Origin of the Yueguang gold deposit in Xinhua, Hunan Province, South China: insights from fluid inclusion and hydrogen–oxygen stable isotope analysis

Origin of the Yueguang gold deposit in Xinhua, Hunan Province, South China: insights from fluid inclusion and hydrogen–oxygen stable isotope analysis

Preservation of bone organic fraction is not predictive of the preservation of bone inorganic fraction when assessing stable isotope analysis sample quality control measures

Stable isotope analysis of carbon (C), nitrogen (N), hydrogen (H), and oxygen (O) of archaeological bone has become an increasingly common research method for interpreting human behavior in the past. However, diagenesis of skeletal material can invalidate stable isotope ratios, thereby compromising interpretations. We examine patterns of bone diagenesis using infrared spectroscopy of bone bioapatite samples in relation to indicators of organic preservation quality indicators. We assess crystallinity, an indicator of bioapatite preservation, using the infrared splitting factor (IR-SF) and carbonate content (carbonate to phosphate ratio, C/P) calculated from infrared spectra. We then test the assumption that if the organic fraction of bone is preserved, the mineral fraction will also be unaffected by postmortem chemical alteration. We analyzed 454 bone bioapatite and extracted bone organic sample pairs from modern, historic, and prehistoric humans. Consistent with previous studies, we observed a strong, statistically significant negative linear relationship between IR-SF and C/P (r = −0.855, p < 0.001). Modern bone bioapatite samples unaltered by diagenesis have low IR-SF and high C/P values. There was no significant association between the collagen yield or atomic C:N ratio and IR-SF or C/P values. The range of variation in IR-SF and C/P values for samples with organic yields between 0 and >20 percent spanned the range of modern bone bioapatite unaltered by diagenesis as well as bone bioapatite significantly affected by diagenesis. The lack of predictive patterning between bone inorganic and organic diagenesis suggests that the depositional context and site formation history play critical and independent roles in the organic and mineral fraction of bone. Thus, the preservation of the organic fraction of bone is not predictive of the preservation of the inorganic fraction (e.g., bioapatite).

Sensitivity of the thermohaline circulation during the Messinian: Toward constraining the dynamics of Mediterranean deoxygenation

During the Messinian, the sensitivity of the Mediterranean Basin to ecosystem perturbation was enhanced in response to the progressive restriction of water exchange with the Atlantic Ocean. The widespread deposition of organic-rich layers (i.e. sapropel) during the Messinian testifies the perturbation of the carbon and oxygen cycles; indeed, these sediments were deposited under conditions of oxygen starvation, presumably in response to a periodic deterioration of the thermohaline circulation strength. Disentangling the causes, the effect and magnitude of the thermohaline circulation weakening during the geological past is crucial for better constraining present and near-future deoxygenation dynamics in the Mediterranean region under the current climate warming. For this purpose, we investigate a Messinian sapropel-bearing succession cropping out at Monte dei Corvi (Ancona, central Italy) with mineralogical, petrographic, micropaleontological and stable Carbon and Oxygen isotopic analyses. We show that sapropel layers were deposited in response to an increase of the sea surface buoyancy, which hampered the thermohaline circulation and thus the oxygenation of bottom water, in turn affecting the bioturbating organisms. Within the lithological cycle, the recovery of an efficient thermohaline circulation is recorded by thin packstone layers underlying the marly limestone/marlstone, which record intense bottom currents. The marly limestone/marlstone accumulated during periods of intense primary productivity and organic carbon export to the sea bottom, which promoted bottom hypoxia but not organic matter preservation. We infer that these lithological changes resulted from variations in the Adriatic Deep Water formation system, controlled by precession-driven climatic and oceanographic changes.By integrating previously published Sea Surface Temperature (SST) with new isotopic and mineralogical data, we show that variations in Sea Surface Salinity (SSS) were the leading factor controlling sapropel deposition, minimizing the role of primary productivity. The SSTs characterizing the sapropel deposits are close to the range of those projected in the Eastern Mediterranean at the end of this century under climate warming. In this scenario, future warming will be coupled with SSS increase, which will counteract the density loss provided by temperature, making the bottom deoxygenation in the Eastern Mediterranean abysses unlikely. However, additional forcing, such as winter heat waves and eutrophication, could contribute to negatively affecting the Mediterranean oxygen balance and should be considered in model-based projections.

Isotopic evidence of an environmental shift at the fall of the Kushite kingdom of Meroë, Sudan

Between c. 300 BC and AD 350, the Meroitic kingdom dominated the Middle Nile Valley; following its breakdown, it was replaced by a series of smaller successor polities. Explanation for this change centres on socio-political and economic instability. Here, the authors investigate the role of climate and environment using stable carbon and oxygen isotope analyses of human and faunal dental enamel from 13 cemeteries. The results show increasing δ18O values towards the end of the Meroitic kingdom and in the post-Meroitic period, combined with less negative δ13C values. These trends suggest a shift towards more arid conditions associated with changes in agricultural practices and land use that may have contributed to the kingdom's dissolution.

A passive method for sampling water in the soil-plant-atmosphere continuum for stable hydrogen and oxygen isotope analyses.

Hydrogen and oxygen isotopes in water molecules are powerful tools to constrain the dynamics of water cycling within the soil-plant-atmosphere continuum (SPAC). However, the recovery of water from the SPAC requires logistical arrangements and implementation of different time- and cost-consuming techniques in either the field or the laboratory. We developed a passive method to sample water from the three compartments of the SPAC by using a hygroscopic salt of a high water absorbance capacity (CaCl2 ). This method allows either H2 O(V) -H2 O(L) isotope equilibration in the case of infinite water reservoir (atmospheric water vapor (WV)) or quantitative absorption of water from a finite water reservoir (e.g. soil and plants). The water absorbed by CaCl2 was distilled first and subsequently processed for hydrogen and triple oxygen isotope mass spectrometry analyses. The distillation step can be bypassed when employing isotope analytical techniques that are based on equilibration. Our experiments show that anhydrous CaCl2 absorbs WV of 210 ± 6% and 130 ± 6% of its dry weight from an infinite WV reservoir at relative humidity of 60% and 30%, respectively. Chemical and isotope equilibrations between WV and absorbed water were attained within 3 days at room temperature, enabling the back-calculation of the isotope composition of atmospheric WV. Preliminary experiments to extract water from plant and sand (i.e. finite WV reservoir) demonstrate a quasi-complete recovery of water in these matrices without significant isotope fractionation. The reproducibility of our method is better than 1.6‰, 0.32‰, 0.17‰ and 6‰ per meg for δ2 H, δ18 O, δ17 O and 17 O-excess. The CaCl2 -H2 O absorption (passive) method requires very limited logistics in the field facilitating spatial and temporal water vapor/water sampling from atmosphere and soil at low resolution (i.e. average of 3-5 days). Moreover, it allows high sample throughput for the extraction of plant water in the laboratory. The reproducibility of this method is similar to the analytical uncertainty in mass spectrometry analyses.