Stable Oxygen Isotope Composition Research Articles

Rapid decrease of the Labrador Sea’s influence on black spruce ecosystems with distance inland

In eastern Canada, Black spruce (Picea mariana Mill. B.S.P.) grows in a wide variety of climates, from maritime-oceanic conditions near the Labrador Sea, to more continental climates, inland. Along this gradient, timing and provenance of heat and moisture that support growth are uncertain, weakening our capacity to predict the response of boreal ecosystems to climate variability. Here, we measured the stable oxygen isotopic composition of black spruce tree-ring cellulose at three sites in eastern Canada and provide evidence of a rapid decrease of Labrador Sea’s influence on adjacent ecosystems. Our results report a landwards decrease in the oxygen isotope composition of both tree-ring cellulose (δ18OTRC) and precipitation water (δ18Op). We also reveal a rapid landwards decoupling between δ18OTRC variability (1950-2013), maximum temperature and Sea Surface Temperature variations over the Northwest Atlantic. Thus, despite their apparent ecological homogeneity, eastern Canada’s black spruce ecosystems rely on heterogeneous sources of heat and moisture.

Application of geochemical tracers for the investigations of groundwater resources in semi‐arid region (Central‐East Tunisia)

AbstractGroundwater resources in Mahdia‐Ksour Essef region, located in the central‐eastern part of Tunisia, suffer from intensive exploitation and degradation of water quality. The assessment of groundwater vulnerability, the well‐understanding of geochemical processes and the investigation of groundwater quality variations are of particular importance for water resources management in this semi‐arid region. The results of this multi‐disciplinary investigation show that groundwaters of Mahdia‐Ksour Essef region are flowing from El Jem and Boumerdes regions in the South, towards the Mediterranean Sea and the sebkha of Moknine in the North. The groundwaters are classified as either Na‐Cl or Ca‐SO4. Stable oxygen and hydrogen isotope compositions (δ18O and δ2H) confirm a recharge by rapid water infiltration, evaporate surface water and water‐rock interaction processes in the salinity increase. The rock‐water interaction processes of the mineralization of groundwaters include the cation‐exchange reactions and the dissolution of carbonates and evaporate. The high values of the water quality index (WQI) and of the total dissolved solids (TDS) (3.7–11 g/L) of these groundwaters indicate their unsuitability for drinking purpose. Moreover, the combination of the WQI, TDS and nitrate results prove the vulnerability of the studied groundwater to the anthropogenic pollution linked to agriculture and domestic activities and to the salt water contamination.

Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Fieldwork provided well-preserved Laevaptychus sp. ex gr. hoplisus–obliquus specimens from the lower Kimmeridgian of Zengővárkony (Mecsek Mountains, south Hungary). This study presents the stable isotope analysis of these aptychi and control samples from brachiopods (Nucleata and Pygope) derived from the Zengővárkony section bed 3. Rarely observed structures in the upper lamellar layers of the studied laevaptychi revealed 24–32 concentric lamellae that represent primary textural features and indicate excellent preservation. After careful screening for diagenetic effects, stable oxygen isotope compositions yielded seawater temperatures between 20 and 26 °C in good agreement with earlier studies on Jurassic formations, with improved precision. Our research presents for the first time that well-preserved laevaptychi may be a reliable data source for paleoclimate and paleotemperature reconstructions.Graphical abstract

Indian summer monsoon variability during the past ~75 ka based on stable isotope records of sediments from NW India

Here we report continuous and chronologically well-constrained records of stable oxygen (δ18O) and carbon (δ13C) isotope compositions of carbonate nodules (nodular calcretes), and δ13C of sediment organic matters (δ13CSOM) in samples from two (~48 m deep) drill-sediment cores, collected from a paleo-Yamuna channel in the NW Indo-Gangetic Plain in north Haryana. The results were used to reconstruct Indian summer monsoon (ISM) precipitation variability and paleovegetation pattern during the past ~75 ka and present a longer record of ISM variability in the Indo-Gangetic Plain. The δ18O of carbonate nodules (−7.80‰ to −4.04‰, average −6.01‰) shows a good negative covariation with variability in the model-derived intensity of ISM precipitation, indicating it to be a good proxy for ISM variability. We infer intense ISM precipitation during late marine isotope stage (MIS) 5, early and late MIS 3, and early MIS 1 periods, marked by relatively lower δ18O of carbonates. These changes in the ISM intensity are in-phase with the precession-induced changes in the Northern Hemisphere summer insolation. The δ13CSOM (−27.4‰ to −22.3‰, average −25.3‰) indicates C3-dominated vegetation in the Himalayan catchment with a noticeable increase in δ13CSOM during late MIS 4 to early MIS 3, late MIS 3, and early MIS 1 periods, which are characterized by the intense ISM (warm and moist condition). This suggests an increased abundance of C4 plants during the periods of intensified ISM precipitation. The δ13C of carbonate nodules varies from −3.63‰ to 1.56‰ (average −1.55‰). The enrichment in 13C of the carbonates is most likely due to the influence of dissolved inorganic carbon derived from the Himalayan source and/or atmospheric CO2 on the carbonate nodules. Therefore, we suggest that the δ13C of carbonate nodules from the Indo-Gangetic Plain requires a careful evaluation.

Surface occurrence of dawsonite and natural CO2 emanation in Covasna, in the Eastern Carpathians: A stable isotope study

Dawsonite (NaAlCO3(OH)2) is widely known as a CO2 trapping mineral during the geological storage of CO2 (Carbon Capture and Storage). Dawsonite can occur naturally in various geological environments, however only few surface occurrences are known. The Covasna area (Eastern Carpathians) gives an excellent opportunity to study dawsonite in surface outcrop in the Hankó Valley and extend our knowledge about the possible precipitation environments of dawsonite. Based on the detailed petrographic and geochemical investigations of the rock and water samples from this area, formation environment of dawsonite and the concomitant mineral assemblage (e.g. alumohydrocalcite) were constrained. Based on our results, dawsonite and alumohydrocalcite formed at low temperature (7.6–20 °C). Utilizing the stable carbon, oxygen and hydrogen isotope composition of dawsonite separates (δ13CDaw: +8.0 − +10.1 ‰, δ18ODaw: +40.7 − +46.7 ‰, δ2HDaw: −55 - -42 ‰), the isotopic composition of the parental fluid was determined. Our results indicate that the dawsonite formed from a CO2 source, which has mantle origin. In addition, H2O which was present during the formation of dawsonite, had similar hydrogen isotope composition to recent spring waters, whereas the oxygen isotope composition is characterized by more positive values. This oxygen shifts relative to Global Meteoric Waterline might be related to water-rock interaction or contribution of metamorphic/magmatic water and oxygen isotope exchange between H2O and CO2.

Calcification depth of pteropods in the Coral Sea using stable oxygen isotopes

Pteropods are marine holoplanktonic gastropods inhabiting epipelagic and mesopelagic waters with a wide distribution from tropical to polar regions. However, their ontogeny and calcification depth/habitat depth are not well understood. To this end, we analyzed the stable oxygen isotopic composition of five pteropod species (Diacavolinia angulata, Diacavolinia longirostris, Heliconoides inflatus, Limacina bulimoides and Telodiacria quadridentata) from two multicores recovered offshore north-eastern Australia between 15°S and 26°S in the Coral Sea. We applied the Limacina dissolution index (LDX) to evaluate the preservation status of the pteropods, which revealed very good to moderate aragonite preservation at both locations. Comparison of the pteropod shell oxygen isotopic composition with predicted aragonite equilibrium oxygen isotope values implies calcification depths of 50 ± 20 m for D. longirostris and 75 ± 30 m for D. angulata, suggesting that they predominantly calcify in the mixed layer during austral summer. The apparent calcification depths of T. quadridentata and H. inflatus at 90 ± 30 m and 120 ± 30 m at both sites indicate a year-round, lower mixed layer and upper thermocline habitat depth, respectively, while T. quadridentata appear to calcify at temperatures above 22 °C. The calcification depth of L. bulimoides is deeper (100 ± 15 m) at the northern station and shallower (75 ± 30 m) at the southern station that might also hint to a temperature control. The relative narrow calcification depth ranges of the investigated pteropod species in the Coral Sea bolster their potential for reconstructing past ocean conditions at the mixed layer and thermocline.

What causes site-specific intra-event variations of stable isotopes in precipitation in Beijing?

Stable oxygen isotope composition (δ18Op) and deuterium excess (dp) in precipitation carry important climate and hydrological information on the history of water from evaporation, transport to precipitation. This study aims to quantify the effect of potential factors on site-specific intra-event δ18Op and dp dynamics during three precipitation events in a mid-latitude region Beijing, China. The tested factors included moisture source (Ms) and upstream rainout fraction (Up) obtained by HYSPLIT backward trajectory model, radar reflectivity factor (Ze) that corresponds to raindrop size by weather radar, sub-cloud evaporation fractionation (fe) by an isotope-evaporation model, local precipitation amount (Lp) and precipitation intensity (I) by rain gauge, and relative location of the sampling sites (downwind or upwind). Intra-event δ18Op had an amplitude of 10.3‰, and 84% of the variance could be explained, in the descending order of importance, by Ms, site, Ze, fe and I. Intra-event dp had an amplitude of 16.5‰, and 57% of the variance could be explained by fe, site, Ms and I, in the descending order of importance. Absolute values of intra-event δ18Op and dp differed between two sites, 30 km apart, by up to 4.7‰ and 9.7‰, respectively. This site-specificity in δ18Op and dp was mainly caused by differences in rainout effects and I. This work provides new insights into separating the effects of various climatic and hydrological variables on high-frequency dynamics of δ18Op and dp.

Meteorological Analysis on Extremely Depleted 18O Rainfall Events during the Summer in Adelaide, Australia

Abstract The transport of atmospheric water vapor plays a crucial role in the production of precipitation and the variation of precipitation isotopic composition (δ18Op). This study investigates three precipitation events with extremely depleted heavy isotopes in the summer of Adelaide, Australia. Using fundamental water vapor diagnosis and moisture calculation method, this research analyzes the impact of rainout degrees along moisture transport paths, atmospheric circulation patterns, water vapor sources, and moisture transport on the extreme depletion of precipitation isotopes in the study area. The purpose of this study is to reveal the direct cause of extremely depleted δ18Op at the hourly time scale. The results show the diversity and complexity of δ18Op variation in summer precipitation events in Adelaide. The rainout caused by local and upstream large precipitation may be the main reason for extremely low values of δ18Op. The phenomenon of subcloud secondary evaporation, which is driven by the interaction between relatively low humidity and high temperature at near-surface levels, plays a pivotal role in the entire precipitation process. This mechanism is particularly pronounced during the onset or cessation of precipitation events, thereby resulting in the observed enrichment of δ18Op values. The oxygen stable isotopic composition of water vapor (δ18Oa) would usually become higher, when the air mass mixes with new moisture with relatively high δ18Oa, suppressing the influence of the previous rainout.

Carbonate-associated sulfate as an archive of sulfur and oxygen stable isotope composition of seawater sulfate: Evidence from reef carbonate rocks of the southern South China Sea

Carbonate-associated sulfate (CAS) is a useful proxy for the reconstruction of the isotopic composition of ancient seawater sulfate, archiving information on the global sulfur cycle, Earth's surface redox evolution, and biological activity. The CAS proxy is possibly compromised by early diagenetic alteration, which may cause secondary inhomogeneities in the isotopic composition of pore water sulfate achieved in the form of CAS. However, the effects of early diagenesis on the retention of primary δ34S signals of CAS in reef carbonates are not well understood, and it is unknown whether reef carbonate deposits can faithfully record the coeval isotopic composition of marine sulfate. To provide new constraints on the resilience of CAS isotopic signatures of reef carbonate, we have measured and analyzed CAS content and CAS isotopic composition of reef carbonates from the Meiji Atoll (well NK-1) of the South China Sea, representing carbonates affected by meteoric and marine diagenesis including dolomitization. CAS contents were found to decrease rapidly during meteoric and marine diagenesis, with minimum CAS contents caused by prolonged subaerial exposure. Despite low contents, the corresponding δ34SCAS values were found to vary within a narrow range from 21.5 to 24.1‰, compared to values of 20.9 to 22.7‰ of coeval barite, suggesting that the original δ34SCAS values are preserved and largely unaffected by recrystallization. However, δ18OCAS values were found to vary widely, ranging from 7.1‰ to 15.0‰, only recording the same oxygen isotope signal as coeval marine barite for reef carbonates younger than 5 Ma. Our data reveal that reef carbonates can be used as an archive of paleoceanic change, faithfully tracking δ34S changes in coeval seawater regardless of whether reef carbonates underwent recrystallization, including dolomitization. In contrast to sulfur isotopes, the oxygen isotope composition of CAS is more susceptible to alteration during diagenesis. Overall, this study provides new insight for the future reconstruction of the sulfate sulfur and oxygen isotope record of ancient seawater.

Moisture sources and climatic effects controlling precipitation stable isotope composition in a western Mediterranean island (Pianosa, Italy)

The Mediterranean basin is indicated as a hot spot of climate change, which is an area whose climate is especially responsive to variations. The insular environment is one of the most threatened by the current climate change, especially in terms of drought events, with serious consequences for water scarcity and water stress. This issue is even enhanced in small islands, whose ecosystems are among more sensitive to climatic changes and water availability. The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in precipitation is globally recognized as a powerful natural tracer in the water cycle and represents the starting point to investigate hydrological processes. The understanding of the prevailing factors that drive the isotopic variability of precipitation in the Mediterranean is therefore essential to unravel the hydrological processes and to ensure proper and sustainable management of potentially vulnerable resources to climate change. Here, we discuss the results of multi-year isotopic monitoring in the period 2014–2021 of monthly precipitation collected on Pianosa Island (Italy), a small island located in the northern Tyrrhenian (western Mediterranean). The lower slope and intercept of the Local Meteoric Water Line of the island compared to the Global Meteoric Water Line indicated warmer and drier climatic conditions, suggesting the existence of sub-cloud evaporation processes of raindrops during precipitation, especially in summer. The mean δ18O of precipitation was lower with respect to other sites placed at higher elevation in this Mediterranean region, due to the lack of summer precipitation which were generally enriched in heavy isotopes. Temperature and amount effects may explain part of the δ18O variability observed at the monthly and seasonal scale. An HYSPLIT-based moisture uptake analysis indicated the area between the western Mediterranean basin, Italy, and the Adriatic Sea as the region that supplied most of the humidity associated with monthly precipitation samples on Pianosa Island. Less moisture was picked from the northwestern areas of Europe, the North Atlantic Ocean, the proximal Atlantic Ocean, the Iberian Peninsula and North Africa. Consistently with the rainout effect, the higher the moisture fraction picked from the more proximal regions, the more positive the δ18O of precipitation occurring on Pianosa Island; conversely, the higher the percentage of moisture sourced from more distal regions, the more negative the δ18O. A multiple linear model was proposed to predict the δ18O of monthly precipitation from temperature, precipitation amount and moisture origin data, which explained 45% of the δ18O variability. The deuterium excess variability on the island was partly controlled by the local climatic variables, whose effect potentially modifies the original d-excess signature imprinted at the moisture source. No relationship was found between the precipitation deuterium excess and moisture sources, suggesting that more attention should be paid when using the deuterium excess as a tracer of moisture origin, especially in the Mediterranean.

Machine Learning Solutions to Regional Surface Ocean δ18O‐Salinity Relationships for Paleoclimatic Reconstruction

AbstractStable isotope‐based reconstructions of past ocean salinity and hydroclimate depend on accurate, regionally constrained relationships between the stable oxygen isotopic composition of seawater (δ18Osw) and salinity in the surface ocean. An increasing number of δ18Osw observations suggest greater spatial variability in this relationship than previously considered, highlighting the need to reassess these relationships on a global scale. Here, we use available, paired δ18Osw and salinity data (N = 11,119) to create global interpolations of each variable. We then use a self‐organizing map, a specialized form of machine learning, to define 19 regions with unique δ18Osw‐salinity relationships in the surface (<50 m) ocean. Inclusion of atmospheric moisture‐related variables and oceanic tracer data in additional self‐organizing map experiments indicates global surface δ18Osw‐salinity spatial patterns are strongly forced by the atmosphere, as the SOM spatial output is highly similar despite no overlapping input data. Our approach is a useful update to the previously delimited regions, and highlights the utility of neural network pattern extraction in spatiotemporally sparse data sets.

Chemotrophy-based phosphatic microstromatolites from the Mississippian at Drewer, Rhenish Massif, Germany

Abstract The Drewer quarry located in the Rhenish Massif is a well-studied outcrop that comprises Upper Devonian (Famennian) to Lower Carboniferous (Viséan) strata. Within the Drewer deposits two black shale intervals have been described that are linked to two global oceanic anoxic events, the Hangenberg Event and the Lower Alum Shale Event. The black shales associated with the Middle Tournaisian Lower Alum Shale Event contain abundant phosphatic concretions, which were investigated using thin section petrography, powder X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy. The concretions formed during several growth phases under anoxic and at least episodically sulphidic conditions within the sediment and served as a substrate for subsurface microbial mats that formed phosphatic microstromatolites. The microstromatolites occur either as partially branched columns of up to 600 µm in length attached to the phosphatic concretions or as smaller, bulbous aggregates surrounding the concretions. Element mapping identified the presence of pyrite and other metal sulphides within the phosphatic microstromatolites. The carbon and oxygen stable isotopic composition of phosphate-associated carbonate within the phosphatic microstromatolites suggests that the mat-forming microorganisms were probably anaerobic, chemotrophic microbial communities dwelling in the anoxic environment during the Lower Alum Shale Event. Such interpretation agrees with the deeper-water depositional setting of the Lower Alum Black Shale and its high content of organic matter, suggesting that chemotrophic microbial mats are potent agents of phosphogenesis in general, and of the formation of phosphatic stromatolites in particular.

Geochemical investigation of the mixed Máriahalom vertebrate fauna at the Paleogene–Neogene boundary in the Central Paratethys: environmental conditions and age constrain

The fossil vertebrate fauna of Máriahalom contains remains from a wide range of ecologies including terrestrial and aquatic mammals, crocodiles, sharks, and rays among others. All these were found mixed in mollusc-rich, shallow water, coastal deposits. The aim of the study is to trace the origin of the fossils using their rare earth element (REE) content and their respective ecology with stable oxygen isotopic compositions. In addition, marine vertebrates and calcareous marine fossils were analysed for their Sr isotope composition to provide a new age estimate for the locality. The REE content and their distribution in the fossils indicate similar early diagenetic environments and possible contemporaneous fossilization for the entire vertebrate assemblage. Reworked fossils of significantly different age can be excluded. The enamel/enameloid-derived phosphate oxygen isotope composition of selected fossil taxa fit well with previously inferred habitats that include marine, brackish, and terrestrial environments. Notably, the stem-pinniped Potamotherium valletoni is best interpreted as freshwater dweller instead of marine, consistent with the sedimentology of other occurrences. Our novel 87Sr/86Sr data suggest an Aquitanian age (21.4 ± 0.5 Ma) for the Máriahalom site that is younger than the previously proposed Late Oligocene age based on biostratigraphy (MP28–30 European Mammal Paleogene Reference Levels). An Aquitanian age raises the possibility that the index fossil taxon, the anthracothere mammal Microbunodon minimum, may have vanished earlier in Western Europe than in the Central Paratethys region.

Multi-isotopic analysis reveals the early stem turtle Odontochelys as a nearshore herbivorous forager

IntroductionAfter decades of debate on the origin of turtles, it is now widely accepted that they are diapsid reptiles originating in the Permian from a terrestrial ancestor. It seems that the initial development of the structures that will later form the unique turtle bony shell took place as a response to a fossorial lifestyle. However, the earliest stem turtle with a fully complete plastron, Odontochelys semitestacea from the Late Triassic (lower Carnian) of China, is somewhat controversially interpreted as an aquatic or even a marine form, raising the question of the environment in which the completion of the plastron happened.MethodsHere, we analyzed the stable carbon, oxygen and sulfur isotope compositions (δ13C, δ18O and δ34S) of bones from two specimens of Odontochelys along with bones and teeth of two associated specimens of the marine ichthyosaur Guizhouichthyosaurus tangae.Results and discussionWe first show that δ18O values of Odontochelys are incompatible with a terrestrial lifestyle and imply a semi-aquatic to aquatic lifestyle. Isotopic results also demonstrate that the aquatic environment of Odontochelys was submitted to a strong marine influence, therefore excluding the possibility of a strict freshwater aquatic environment. Additionally, an unusual carbon isotope composition shows that O. semitestacea was herbivorous, probably consuming macrophytic algae in coastal zones like the extant green sea turtle (Chelonia mydas) or the marine iguana (Amblyrhynchus cristatus) do.

Origin and evolution of Li-rich geothermal waters from the Kawu geothermal system, Himalayas: based on hydrochemistry and H-O, Li isotopes

ABSTRACT There are 25 Li-rich geothermal fields (>15 mg/L) are displayed throughout nine geothermal zones in Tibet. The Kawu geothermal system is one of the representative high-enthalpy and Li-rich geothermal systems and is located in the Skaya dome, the Himalayas. Their boiling and hot and cold waters are Cl-HCO3-Na and HCO3-Ca types, respectively. The parent geothermal fluids are characterized by high Na, Cl, B, Si, As, Li, Rb+, Cs+ and F, and the Cl− concentration and enthalpy of the parent geothermal liquid are 515 mg/L and 1,485 J/g, respectively (corresponding to a temperature of 323.5°C). The stable oxygen and hydrogen isotopic compositions of geothermal fluids range from −19.7 to −23.4‰ and −155 to −181.2‰, indicating that the ratio of magmatic water mixed into geothermal fluid is between 11.7% and 19.5%. The lithium content in the geothermal system is high (13.04 to 20.8 ppm), but the δ7Li is relatively low (1.06 to 1.72‰). The high Cl, Li and B contents, constant Cl/Li and Cl/B ratios and low δ7Li indicate that they mainly originate from magmatic fluid, rather than from water rock reaction with the leucogranite and gneiss. While ascending from the reservoirs to the surface, the parent geothermal fluids gradually mixed with the meteoric waters infiltrated via brittle tensional small-scale faults, in turn forming four cooling processes upwelling patterns, i.e. conductive cooling, adiabatic cooling, mixing with cold water, and the combination of these processes.

A multi-region study of carbonate clumped isotope data from terrestrial snails

The stable oxygen isotope composition (δ18O) of land snail shells has been used for decades to provide insight into past changes in δ18Oprecipitation, relative humidity, moisture source and several other paleoenvironmental parameters across diverse environments and ecosystems. Recently, carbonate clumped isotope values (Δ47) recorded from land snail shells have also been applied as a geothermometer. However, there is limited information available regarding the relationship between modern shell geochemistry and paleoenvironmental conditions for regions with contrasting climates, which is needed for further contextualization and validation of snail shell temperature proxies. Our study utilizes paired Δ47 and δ18Oshell measurements in terrestrial snail shells to reconstruct temperature (T47) and δ18Obody water composition, which are two key variables used for the study of regional and sub-regional paleoclimates and paleoecosystems. We examine shells from three geographical regions with distinct hydroclimates: Central Europe, the Canary Islands, and the Chinese Loess Plateau. To constrain the timing of shell growth, we compare snail shell isotope-derived climate parameters to independent environmental data, including mean annual, warm season, and rainy season temperatures, assuming snail shells mineralize during the optimal activity range of 15–25 °C. Our results indicate that values for samples from the Canary Islands are most consistent with year-round growth; Chinese Loess Plateau samples are most consistent with summer growth; and samples from Central Europe are most consistent with growth between spring and autumn. Calculated values of δ18O body water in snail shells were found to be enriched relative to the value of δ18Oprecipitation for the season of growth, with values ranging from ∼1–5‰. Altogether, our data suggest that Δ47 and δ18O measurements from terrestrial snail shells represent a useful archive of environmental temperature and humidity. However, their application in the paleo-record requires careful consideration of the ecophysiology of the taxa, and the climate of the region.

A speleothem record of seasonality and moisture transport around the 8.2 ka event in Central Europe (Vacska Cave, Hungary)

AbstractA stalagmite was collected in northern Hungary from the Vacska Cave, where monitoring and ventilation-based site selection had been conducted. The stalagmite covers the 10–8 ka (relative to AD 1950) period, including the so-called 8.2 ka event, and showed preceding signs of climate change that were evaluated by petrographic observations, 14C activities, Sr concentrations, and stable isotope compositions of calcite and inclusion-hosted water. Comparisons of speleothem records show that isotope peaks at ca. 8.5 ka are related to a regional climate anomaly, rather than to a continental-scale event. In accordance with regional proxy records, the 8.2 ka event was associated with a series of temperature and precipitation amount changes, starting with cooling and a reduction in the winter-to-summer precipitation ratio, and then becoming a humid and warm phase at 8.15 ka. X-ray diffraction-based crystallinity parameter (FWHM) values provided evidence for diagenetic alteration of the stable oxygen isotope compositions of inclusion waters. Nevertheless, the stable hydrogen isotope compositions of inclusion waters and the oxygen isotope values of the host calcite revealed elevated d-excess values, and therefore increased Mediterranean moisture contribution during the 8.2 ka event, which indirectly indicate the southward displacement of moisture transport from the Atlantic Ocean.

Feeding habits of a latest Pleistocene megamammal community. A synecological perspective by stable isotopes analysis

The coexistence and interaction between the Pleistocene megamammals and the first human groups have been mainly addressed extrinsically, without considering the megafauna's paleoecology. This study used the stable carbon and oxygen isotopic composition of carbonate fraction of well-preserved fossils to deepen the knowledge of these latest megamammals. We focus on an Argentine Pampas area, where they are concentrated archaeological and paleontological contexts with radiocarbon ages for the final Pleistocene. We employ Bayesian mixing models, built through quantitative diet information for modern analogs, a novel methodological approximation for the study area. The results indicate that the megamammals of the final Pleistocene Pampas were in equilibrium with the ecosystem, showing signs of resource natural cycles. Those rhythms suppose differential distribution and availability of these animals.

The measurement of ambient air moisture stable isotope composition for the accurate estimation of evaporative losses

Accurate estimation of evaporative losses from a water body, using the Craig-Gordon model and the stable hydrogen and oxygen isotope composition of water, requires knowledge of the stable isotope composition of ambient air moisture. This is rarely measured in the field, and it is usually estimated assuming that recent rainfall remains in isotopic equilibrium with atmospheric moisture. However, the ambient air moisture stable isotope composition may vary significantly at different heights above the water body.In this study, we set up outdoor pan evaporation experiments and simultaneously measured the stable isotope composition of ambient moisture in the atmosphere at three different heights. Using these measurements, we calculated evaporative losses, compared them with the observed losses in the pan, and assessed the uncertainty introduced by differences in ambient moisture measurements.Three main steps in the experimental method:•Daily water sampling from the evaporation pan for analysis of stable hydrogen and oxygen isotope compositions.•Recording the stable isotope composition of ambient air moisture at three different heights using the Picarro L2130-i system over a period of experiments.•Calculating evaporative losses from the pan using the Craig-Gordon model and ambient air stable isotope composition measured at three different levels and comparing to the observed losses.

An explainable machine learning for geographical origin traceability of mussels Mytilus edulis based on stable isotope ratio and compositions of C, N, O and H

Geographical traceability of marine bivalves has been explored continually, however the traceability results have not been recognized owing to the absence of a reasonable explanation for a certain model prediction. To address this problem, we employed an explainable machine learning to identify the origin of mussels based on stable isotope ratio and compositions of carbon (C), nitrogen (N), oxygen (O), and hydrogen (H). Our findings proved that the Extreme gradient boosting (XGBoost) model may be the best model based upon its high accuracy (93.75 %), precision (93.75 %), recall (94.51 %), F1 score (93.72 %) and AUC (0.990). The feature impact for model out of XGBoost was interpreted by SHapley Additive exPlanations (SHAP) on global and local perspective. This study demonstrated the potential of explainable machine learning to elucidate the complex relationships between desirable geographical information of mussels and the selected features.