Oxygen Isotope Signatures Research Articles

The triple oxygen isotope signature of uranium oxides in the nuclear fuel cycle

Uranium oxides, in the form of U3O8 and UO2, are principal compounds in the uranium nuclear fuel cycle and attract significant interest in the general field of nuclear forensics, for the development of new and credible signatures to support attribution. This study presents, for the first time, the analytical method and high-precision measurements of the triple oxygen isotope composition of U3O8 and UO2. We show that Δ’17O can be measured at the accuracy and reproducibility needed for nuclear forensics. Δ’17O exhibits a wide range, from -450 to -120 ppm, for both commercial and synthetic uranium oxides. The presentation of the data in Δ’17O-δ’18O space provides a two-dimension identification of uranium oxides for nuclear forensic characterization of samples. The relation between Δ’17O and the process from which the oxide was formed or manipulated, has the potential to trace the chemical history of the material. We determined the change in Δ’17O of the system U3O8 – atmospheric O2 resulting from isotope exchange at the temperature range of 298 K to 973 K. The dependency of the triple isotope exponent, θ, on temperature was calculated for this exchange reaction, concluding that the phase transition from pseudo-hexagonal to hexagonal structure plays a major role in determining Δ17O and θ. A set of reduction reactions of U3O8 to UO2 indicate that Δ’17O undergoes minimal change during this process.

Oxygen Isotopes of Iron Oxides as a Diagnostic Tool for Iron Formation-Hosted High-Grade Magnetite-Hematite Deposits

Coarse-grained granoblastic magnetite-hematite and sheared platy hematite iron orebodies comprise several small deposits (5 to 30 Mt each) on the eastern margin of the São Francisco Craton, bordering the Ediacaran–Cambrian Brasiliano Orogenic belt. Three main mineralization stages are associated with the Brasiliano Orogeny: (1) syn- to the late-collisional stage (ca. 580–560 Ma) with development of lens-shaped schistose orebodies along thrust planes. (2) late- to the post-collisional stage (ca. 560–530 Ma) with the formation of massive magnetite bodies by contact metamorphic-metasomatism with pegmatite. (3) Post-tectonic stage with crystallization of granular hematite associated with late pegmatite (ca. 530–490 Ma). In order to better evaluate the fluid oxygen signature of each mineralization stage, new oxygen isotopes measurements were performed on ore bodies associated with the three stages. These stages are followed by changes in the oxygen isotope signature, with a progressive decrease of the δ18O from the iron formation (1.7 to 8.1‰) to high-grade ore (-1.6 to 2.6‰) that appears to be a common aspect of the mineralization of iron formations. In the present cases, magmatic fluids (δ18O from 4.6 to 13.1‰) have imprinted a relatively “heavier” signature than the most hypogene iron formation high-grade ores worldwide that was progressively modified by meteoric water percolated along extensional fractures. The iron oxides from the contact zones of pegmatitic yielded intermediate δ18O values (1.8 to 5.0‰), indicating a higher magmatic fluid/rock ratio.

Significance of conodont data for explaining geosystem perturbations during the Middle Devonian Kačák Episode

The present review of published data as well as the new results demonstrate the versatility of conodonts in documenting and explaining global environmental fluctuations related to the Kačák Episode (KE) in the latest Eifelian. Although the conodont zonation of the KE interval is ambiguous and requires revision, the compilation of conodont stratigraphic ranges shows their potential for a precise worldwide correlation of relevant marine strata. Conodont biofacies may serve to document environmental changes connected with KE, in particular the sealevel rise at its beginning, followed by a regressive trend. Nevertheless, the familiar Icriodus/Polygnathus ratio should be carefully applied as an indication of water depth and nearshore vs. offshore position, being controlled also by other factors, such as paleolatitude and/or climate. Oxygen isotopes in conodont apatite, studied using secondary ion mass spectrometry technique evidence a warming at the onset of KE, based on the new data from the open marine facies of the Prague Basin. At the same time, they indicated climate-controlled salinity fluctuations in the epeiric Belarusian Basin. The present investigations as well as previous results suggest caution when analyzing thermally altered conodonts which may result in biased oxygen isotope signatures. The present experience suggests the conodont colour alteration index CAI 3 as a boundary value above which the caution is necessary.

Heavy silicon and oxygen isotope signatures of TTGs formed in distinct tectonic settings

Tonalite–trondhjemite–granodiorite suites (TTGs) are key components of Archean continental crust and are therefore crucial to understanding the evolution of Archean Earth. However, the tectonic settings of their formation remain unresolved. Here we present new in situ zircon Si–O–Hf isotopes and quartz Si–O isotopes from 2.95 to 2.54 Ga TTGs of the Jiaodong terrane in the North China Craton. Through first-principles calculations, the corresponding TTG melt δ30Simelt and δ18Omelt values are determined as –0.03 ‰ to 0.06 ‰ and 7.12 ‰ to 7.60 ‰, respectively, indicating heavier isotope signatures than those of mantle-derived juvenile rocks. The 2.95–2.93 Ga and 2.56–2.54 Ga TTGs have depleted Hf isotopes [εHf(t) = +3.7 to +4.9, and +2.5 to +5.5, respectively] and higher (La/Yb)N ratios compared with the 2.75–2.71 Ga TTGs, which have relatively less depleted Hf isotopes [εHf(t) = +0.9 to +2.0] and lower (La/Yb)N ratios. Although the heavy Si–O isotope compositions indicate the involvement of supracrustal materials in the melting sources of all studied TTGs, the variable zircon Hf isotopes and (La/Yb)N ratios suggest that these rocks formed in distinct tectonic settings. The 2.95–2.93 Ga and 2.56–2.54 Ga TTGs are inferred to have been generated in a subduction setting involving the melting of juvenile oceanic crust under high-pressure conditions, whereas the 2.75–2.71 Ga TTGs are inferred to have been derived from the melting of buried ancient oceanic crust under a mantle-plume-induced lower-pressure environment. We conclude that the heavy Si–O isotope signatures of Archean TTGs may not be directly related to plate-tectonic processes.

Hydrogen and oxygen isotope signal transmission in rainfall, soil water, and cave drip water in Liangfeng Cave, Southwest China

δD and δ18O isotope signatures were widely used as tracers to investigate recharge processes of rainfall transfer into caves in the vadose zones of karst regions. The present research systematically monitored rainfall, soil water, and drip water at the Liangfeng Cave in Guilin City, China, from January 2020 to September 2022, as these aspects remain poorly quantified. The δD and δ18O compositions of rainfall were depleted during the rainy season and enriched during the dry season. The local meteoric water line (LMWL) was described as δD = 7.98δ18O + 11.52. The dry season is mainly characterized by resident soil water, with little mobile soil water, whereas the primary source of recharged drip water is stored bedrock water on the top of the cave. During the rainy season, resident and mobile soil water exchanged with each other, resulting in homogenous δD and δ18O compositions across different soil depths and indicating a lack of ecohydrological separation; however, δD and δ18O signature in drip water may differ from the original observed in rainfall, suggesting that the residence time affected the response time of the drip water to rain. Moreover, mixed stored older water in the overlying bedrock was the primary drip water recharge source each season; thus, drip water's isotope amplitude values were more depleted than rainfall's. Distinct flow paths also created differences in the lag time and amplitude at each drip site. During high-intensity rain, the isotopic signals were rapidly transmitted by preferential flow at different soil depths and via drip water. The δD and δ18O signals in the drip water showed significant depleted excursions several months after high-intensity rainfall. These findings indicate that ecohydrological separation did not occur under any circumstances within the study area, and care should be taken when interpreting significant depleted excursions of δD and δ18O signals in drip water during the summer monsoon or the amount of rainfall in stalagmites across seasonal or interannual scales.

Exploring the Deuterium Excess of Cretaceous Arctic Paleoprecipitation Using Stable Isotope Composition of Clay Minerals from the Prince Creek Formation (Maastrichtian) in Northern Alaska

We report estimated stable isotope compositions of Artic paleoprecipitation using phyllosilicates sampled from three paleosols and two bentonites in the Prince Creek Formation (Maastrichtian) in northern Alaska. Previous studies reported a deuterium excess in estimates of Arctic paleoprecipitation from the Late Cretaceous by combining hydrogen and oxygen proxy sources, including pedogenic minerals, dinosaurian tooth enamel phosphates, pedogenic siderites, and n-alkane biomarkers. The new dataset produced in this study removes uncertainty on possible explanations (photosynthetic and transpiration) of the deuterium excess by producing stable hydrogen and oxygen isotopic signatures from the same source material. The δD of the phyllosilicates range from −171‰ to −72‰ VSMOW and δ18O ranges from 5.0 to 11.8‰ VSMOW. By assuming a MAT of 6.3 °C and calculating uniquely derived fractionation equations for each phyllosilicate, we report estimated isotopic composition of Late Cretaceous paleoprecipitation with an average δD value of −133‰ VSMOW, corresponding to an average δ18O value of −20.3‰ VSMOW. The estimates of Late Cretaceous paleoprecipitation do not intersect the Global Meteoric Water Line and reveal a reported deuterium excess ranging from 7 to 46 per mil. These results confirm the presence of a deuterium excess in Late Cretaceous Arctic paleoprecipitation and provide new insight to assessing possible explanations for this phenomenon.

Magnetite geochemistry and mineralogy of iron skarn in the southern Wag Water Belt, Jamaica: Implications for ore genesis

The Mavis Bank iron skarn mineralisation is located within a Paleocene to Eocene rift system typified by terrestrial and marine deposits, and extensive lava flows and subvolcanic intrusions of adakitic composition. Iron occurs primarily as massive, lenticular magnetite bodies at the contact between the intrusions and calcic Fe skarn (metasomatised limestone) which grades into a low-grade marble with disseminated magnetite. Magnetite is also disseminated in shales and lavas located within the main mineralised zones. Skarn mineralogy is poorly developed in both the endoskarn and the exoskarn with only minor occurrence of diopside. Retrograde and alteration minerals, such as epidote, chlorite, and hematite, are more common. Sulphides are rare, highly altered, and dominated by pyrite, pyrrhotite, and minor chalcopyrite. Petrographic analysis, including micro-XRF-EDS mapping of polished thin sections, shows that massive magnetite and calcic Fe skarns have minor disseminated Ti and S phases along with trace amounts of Cu and Co. Scanning electron microscope-backscattered electron (SEM-BSE) imaging of the exoskarn highlights the extent of retrograde alteration and later supergene weathering, and the presence of dissolution and reprecipitation features.The in situ trace element composition of magnetite in massive magnetite and calcic Fe skarn was determined using LA-ICP-MS. The results, when plotted on multi-element and discriminant diagrams, including Ni/(Cr + Mn) vs Ti + V, Ca + Al + Mn vs Ti + V, Ti vs V, and Ti vs Ni/Cr, are generally consistent with the geochemical signatures of skarn deposits worldwide. The mineralogy and trace element signatures suggest that the skarn deposit was formed at relatively shallow levels by low temperature hydrothermal fluids with high fO2 and fS. In addition, δ18O values of 6.6 and 7.1 ‰ obtained from massive magnetite are typical of infiltrative skarns and are consistent with a mixture of magmatic and meteoric water, and limestone oxygen isotope signatures.

Precipitation δ18O paced the seasonal δ18O variations of terrestrial snail body water and shells in the East Asian monsoon region

Terrestrial snails are sensitive to climate changes and their shell's oxygen isotope composition (δ18Oshell) is widely used in studies of paleoclimate reconstructions. However, the interpretation of δ18Oshell remains complex due to the combined effects from different factors such as precipitation δ18O (δ18Op), relative humidity (RH), and temperature. Furthermore, no systematic studies have addressed the transformation of oxygen isotope signals from rainfall to the aragonite shell via snail body water. Here we present the results of Cathaica fasciola body water δ18O (δ18OBW) and its content, which were sampled every two days throughout the growing season in 2021 in Xi'an. Meanwhile, the soil water δ18O (δ18OSW), δ18Op, rainfall amount, RH and temperature were also simultaneously monitored, and two high-resolution (at ∼0.3 mm interval) δ18Oshell series were obtained from two live snails collected in September and October 2021, respectively. These data reveal that the δ18OBW mimic the variations of δ18Op, and they are positively correlated (r2 = 0.84) for precipitation events and the correlation coefficient only increases slightly (r2 = 0.88) when RH is included in the multivariate analysis. During non-precipitation intervals, there is an obvious negative correlation between δ18OBW and RH. Moreover, the variations of two δ18Oshell series are broadly consistent with the theoretically calculated δ18Oshell from δ18OBW/δ18Op at seasonal scale. Collectively, this study demonstrates that δ18Op is the first-order control on the seasonal variations of δ18OBW and δ18Oshell, while RH play its role during non-precipitation periods. Importantly, this study lays good foundation for reconstructing terrestrial seasonal distribution of precipitation and extreme rainfall events using fossil shells in the geological past.

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.

Origin of Low-26Al/27Al Corundum/Hibonite Inclusions in Meteorites

Most meteoritic calcium-rich, aluminum-rich inclusions formed from a reservoir with 26Al/27Al ≈ 5 × 10−5, but some record lower , demanding they sampled a reservoir without live 26Al. This has been interpreted as evidence for “late injection” of supernova material into our protoplanetary disk. We instead interpret the heterogeneity as chemical, demonstrating that these inclusions are strongly associated with the refractory phases corundum or hibonite. We name them “low-26Al/27Al corundum/hibonite inclusions” (LAACHIs). We present a detailed astrophysical model for LAACHI formation in which they derive their Al from presolar corundum, spinel, or hibonite grains 0.5–2 μm in size with no live 26Al; live 26Al is carried on smaller (<50 nm) presolar chromium spinel grains from recent nearby Wolf–Rayet stars or supernovae. In hot (≈1350–1425 K) regions of the disk, these grains and perovskite grains would be the only survivors. These negatively charged grains would grow to sizes 1–103 μm, even incorporating positively charged perovskite grains, but not the small, negatively charged 26Al-bearing grains. Chemical and isotopic fractionations due to grain charging was a significant process in hot regions of the disk. Our model explains the sizes, compositions, oxygen isotopic signatures, and the large, correlated 48Ca and 50Ti anomalies (if carried by presolar perovskite) of LAACHIs, and especially how they incorporated no 26Al in a solar nebula with uniform, canonical 26Al/27Al. A late injection of supernova material is obviated, although formation of the Sun in a high-mass star-forming region is demanded.

Climate variability in the northern Levant from the highly resolved Qadisha record (Lebanon) during the Holocene optimum

AbstractNew stalagmites from Qadisha Cave (Lebanon) located at 1720 m above sea level provide a high-resolution and well-dated record for northern Mount Lebanon. The stalagmites grew discontinuously from 9.2 to 5.7 and at 3.5 ka, and they show a tendency to move from a more negative oxygen isotope signal at ~9.1 ka to a more positive signal at ~5.8 ka. Such a trend reflects a change from a wetter to a drier climate at high altitudes. The δ13C signal shows rapid shifts throughout the record and a decreasing trend toward more negative values in the mid-Holocene, suggesting enhanced soil activity. In the short-term trend, Qadisha stalagmites record rapid dry/wet changes on centennial scales, with a tendency to more rapid dry events toward the mid-Holocene. Such changes are characterized by overall good agreement between both geochemical proxies and stalagmite growth and might be affected by the seasonal variations in snow cover. The Qadisha record is in good agreement with other Levantine records, showing more humid conditions from 9 to 7 ka. After 7 ka, a drier climate seems to affect sites at both low- and high-altitude areas. The Qadisha record reflects uniquely mountainous climate characteristics compared with other records, specifically the effect of snow cover and its duration regulating the effective infiltration.

Hydrogen Peroxide Formation during Ozonation of Olefins and Phenol: Mechanistic Insights from Oxygen Isotope Signatures.

Mitigation of undesired byproducts from ozonation of dissolved organic matter (DOM) such as aldehydes and ketones is currently hampered by limited knowledge of their precursors and formation pathways. Here, the stable oxygen isotope composition of H2O2 formed simultaneously with these byproducts was studied to determine if it can reveal this missing information. A newly developed procedure, which quantitatively transforms H2O2 to O2 for subsequent 18O/16O ratio analysis, was used to determine the δ18O of H2O2 generated from ozonated model compounds (olefins and phenol, pH 3-8). A constant enrichment of 18O in H2O2 with a δ18O value of ∼59‰ implies that 16O-16O bonds are cleaved preferentially in the intermediate Criegee ozonide, which is commonly formed from olefins. H2O2 from the ozonation of acrylic acid and phenol at pH 7 resulted in lower 18O enrichment (δ18O = 47-49‰). For acrylic acid, enhancement of one of the two pathways followed by a carbonyl-H2O2 equilibrium was responsible for the smaller δ18O of H2O2. During phenol ozonation at pH 7, various competing reactions leading to H2O2 via an intermediate ozone adduct are hypothesized to cause lower δ18O in H2O2. These insights provide a first step toward supporting pH-dependent H2O2 precursor elucidation in DOM.

Climate change-related growth improvements in a wide niche-breadth tree species across contrasting environments.

The vulnerability and responsiveness of forests to drought are immensely variable across biomes. Intraspecific tree responses to drought in species with wide niche breadths that grow across contrasting climatically environments might provide key information regarding forest resistance and changes in species distribution under climate change. Using a species with an exceptionally wide niche breath, we tested the hypothesis that tree populations thriving in dry environments are more resistant to drought than those growing in moist locations. We determined temporal trends in tree radial growth of 12 tree populations of Nothofagus antarctica (Nothofagaceae) located across a sharp precipitation gradient (annual precipitation of 500-2000 mm) in Chile and Argentina. Using dendrochronological methods, we fitted generalized additive mixed-effect models to predict the annual basal area increment as a function of year and dryness (De Martonne aridity index). We also measured carbon and oxygen isotope signals (and estimated intrinsic water-use efficiency) to provide potential physiological causes for tree growth responses to drought. We found unexpected improvements in growth during 1980-1998 in moist sites, while growth responses in dry sites were mixed. All populations, independent of site moisture, showed an increase in their intrinsic water-use efficiency in recent decades, a tendency that seemed to be explained by an increase in the photosynthetic rate instead of drought-induced stomatal closure, given that δ18O did not change with time. The absence of drought-induced negative effects on tree growth in a tree species with a wide niche breadth is promising because it might relate to the causal mechanisms tree species possess to face ongoing drought events. We suggest that the drought resistance of N. antarctica might be attributable to its low stature and relatively low growth rate.

Provenance of sculptural limestones in protohistoric Provence (SE France): Insights from carbonate rock petrography and stable isotope geochemistry

The combination of a detailed analysis of microfacies, diagenetic features and isotopic signatures (carbon and oxygen) of limestones from protohistoric statues and the comparison with substantial regional petrographic and geochemical databases have proven to be successful for constraining the provenance and providing insights into the production of statuary materials in Provence during the Iron Age. The limestones forming the sculptures from Roquepertuse (twin-headed “Hermes”, the lintel with horses and the warrior seated cross-legged) and Rognac (warrior seated cross-legged) are interpreted to derive from lower Barremian carbonate formations from La Fare Massif, likely from near Coudoux, based on 1) micropalaeontologic markers (orbitolinids), 2) grain size, texture and grain composition (oolitic, oobioclastic and bioclastic grainstones), 3) dissolution features affecting ooid cortices and 4) carbon and oxygen isotope signatures. The bryozoan-echinoderm association and the occurrence of Amphistegina suggest that the bust of warrior from La Cloche oppidum (3rd to 1st century BCE) is made of a Miocene limestone from La Couronne Formation. Its isotope composition suggests a provenance from quarries located at Anse du Verdon or possibly further west. The fragment of scapulary tunic found in a disturbed archaeological context dated of 6th to 2nd century BCE on the Baou de Saint-Marcel oppidum, in Segobrige territories east of Massalia, is made of a vuggy limestone whose clotted peloidal-fenestral fabric and isotope signature are consistent with local, lower Pleistocene travertines. The young male head from the Ziem Museum was made of a planktonic foraminiferal, quartz-free limestone with Heterohelix for which no analogue is known in the region, thus suggesting that its place of manufacture is likely to be located outside Provence. Finally, the analyzed set of limestones from protohistoric sculptures, and of certain Provençal provenance, derive from stone production sites geographically close (<20 km) to the places of discovery. A set of non-invasive in situ techniques has been also used to discriminate among the possible sources (magnetic susceptibility, X-ray fluorescence chemical analysis, sound velocity, photogrammetry), but they appeared non discriminant for the present case.

Nitrogen control of transpiration in grapevine.

Transpiration per unit of leaf area is the end-product of the root-to-leaf water transport within the plant, and it is regulated by a series of morpho-physiological resistances and hierarchical signals. The rate of water transpired sustains a series of processes such as nutrient absorption and leaf evaporative cooling, with stomata being the end-valves that maintain the optimal water loss under specific degrees of evaporative demand and soil moisture conditions. Previous work provided evidence of a partial modulation of water flux following nitrogen availability linking high nitrate availability with tight stomatal control of transpiration in several species. In this work, we tested the hypothesis that stomatal control of transpiration, among others signals, is partially modulated by soil nitrate ( ) availability in grapevine, with reduced availability (alkaline soil pH, reduced fertilization, and distancing source) associated with decreased water-use efficiency and higher transpiration. We observed a general trend when was limiting with plants increasing either stomatal conductance or root-shoot ratio in four independent experiments with strong associations between leaf water status, stomatal behavior, root aquaporins expression, and xylem sap pH. Carbon and oxygen isotopic signatures confirm the proximal measurements, suggesting the robustness of the signal that persists over weeks and under different gradients of availability and leaf nitrogen content. Nighttime stomatal conductance was unaffected by manipulation treatments, while application of high vapor pressure deficit conditions nullifies the differences between treatments. Genotypic variation for transpiration increase under limited availability was observed between rootstocks indicating that breeding (e.g., for high soil pH tolerance) unintentionally selected for enhanced mass flow nutrient acquisition under restrictive or nutrient-buffered conditions. We provide evidence of a series of specific traits modulated by availability and suggest that fertilization is a potential candidate for optimizing grapevine water-use efficiency and root exploration under the climate-change scenario.

Study on recharge source and influence mechanism of plant water in the Three-River Headwaters Region, China

This study, based on the stable isotope tracer technique (δ18O and δ2H), focuses on the recharge sources of plant water in the Three-Rivers Headwaters Region in Qinghai province, China. The oxygen and hydrogen isotope signatures of trees and shrubs were more depleted than those of herbs. However, the d-excess pattern was the opposite of the patterns of stable isotopes of oxygen and hydrogen. From the distribution of stable isotope characteristics of water bodies, the direct source of plant water was determined to be soil water, whereas the indirect sources were river water, supra-permafrost water, soil water, precipitation, and ground ice. The contribution proportions of soil water layers between 0 cm and 20 cm and between 40 cm and 60 cm to the plant water were higher than those of other soil water layers for trees. More importantly, the plant water of shrubs was similar to trees in the cold region. The analysis of the indirect recharge sources of plant water revealed that soil water was still the major source of plant water, while glacier snow meltwater, precipitation, and ground ice meltwater are also the main supply sources of plant water. The proportion of supra-permafrost water to plant water was relatively high, mainly because herbs grow in the active layer in the cold region. Therefore, the proportion of plant water recharged by supra-permafrost water and ground ice meltwater was higher than that of other water bodies during the plant growing season.

Tissemouminites: A new group of primitive achondrites spanning the transition between acapulcoites and winonaites

AbstractThe Northwest Africa (NWA) 090 meteorite, initially classified as an acapulcoite, presents petrological, chemical, and isotopic characteristics comparable to a group of seven primitive winonaites: Dhofar 1222, NWA 725, NWA 1052, NWA 1054, NWA 1058, NWA 1463, and NWA 8614. Five of these samples were previously classified as acapulcoites or ungrouped achondrites before being reclassified as winonaites based on their oxygen isotopic compositions. These misclassifications are indicative of the particular compositional nature of these primitive achondrites. All contain relict chondrules and a lower closure temperature of metamorphism of 820 ± 20 °C compared to other typical winonaites, as well as mineral elemental compositions similar to those of acapulcoites. The oxygen isotopic signature of these samples, δ17O of 1.18 ± 0.17‰, δ18O of 3.18 ± 0.30‰, and Δ17O of −0.47 ± 0.02, is in fact resolvable from both acapulcoites and winonaites. We investigate the relationship between these eight primitive achondrites, typical winonaites, and acapulcoites, to redefine petrological, mineralogical, and geochemical criteria of primitive achondrite classification. Distinguishing between winonaites, acapulcoites, and this group of eight primitive achondrites can be unambiguously done using a combination of several mineralogical and chemical criteria. A combination of olivine fayalite content and FeO/MnO ratio, as well as plagioclase potassium content allow us to separate these three groups without the absolute necessity of oxygen isotope analyses. NWA 090 as well as the other seven primitive achondrites, although related to winonaites, are most likely derived from a parent body distinct from winonaites and acapulcoites–lodranites, and define a new group of primitive achondrites that can be referred to as tissemouminites.

Inter-annual and intra-annual tree-ring oxygen isotope signals in response to monsoon rainfall in northwestern Thailand

We present a new teak ( Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation ( r = −0.678, p &lt; 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy.

High rates of daytime river metabolism are an underestimated component of carbon cycling

River metabolism and, thus, carbon cycling are governed by gross primary production and ecosystem respiration. Traditionally river metabolism is derived from diel dissolved oxygen concentrations, which cannot resolve diel changes in ecosystem respiration. Here, we compare river metabolism derived from oxygen concentrations with estimates from stable oxygen isotope signatures (δ18O2) from 14 sites in rivers across three biomes using Bayesian inverse modeling. We find isotopically derived ecosystem respiration was greater in the day than night for all rivers (maximum change of 113 g O2 m−2 d−1, minimum of 1 g O2 m−2 d−1). Temperature (20 °C) normalized rates of ecosystem respiration and gross primary production were 1.1 to 87 and 1.5 to 22-fold higher when derived from oxygen isotope data compared to concentration data. Through accounting for diel variation in ecosystem respiration, our isotopically-derived rates suggest that ecosystem respiration and microbial carbon cycling in rivers is more rapid than predicted by traditional methods.

Combining metal and sulfate isotopes measurements to identify different anthropogenic impacts on dissolved heavy metals levels in river water

Dissolved heavy metals (DHMs) contamination has raised global concern for ecological and human health development. Weathering of sulfide-bearing ore metals can produce acidic, sulfate-rich solutions in the presence of water and oxygen (O2), and DHMs are released to deprave the river water quality. Sulfur and oxygen isotope signatures (δ34SSO4 and δ18OSO4) could identify this pyrite-derived sulfate; however, it is yet not well known whether the δ34SSO4 and δ18OSO4 values could limit the DHMs sources and illustrate anthropogenic impacts on DHMs along the river corridor. We tried to solve this problem through field works in the Luohe River and Yihe River, two tributaries of the Yellow River, China, where metal sulfide mine activities mostly occurred upstream, but agricultural and domestic behaviors concentrated in the lower plain reaches. In the Luohe River upper areas, δ34SSO4 values had negative correlations with concentrations of cadmium (Cd) (p < 0.01), nickel (Ni) (p < 0.05), molybdenum (Mo) (p < 0.01), uranium (U) (p < 0.01), and SO42− (p < 0.01). However, as the δ34SSO4 values increased downstream in the Luohe River, concentrations of copper (Cu) (p < 0.05), mercury (Hg) (p < 0.05), Ni (p < 0.05), and SO42− (p < 0.01) simultaneously elevated. The Bayesian Isotope Mixing Model (BIMM) results via δ34SSO4 values demonstrated 64.3%–65.3% of SO42− from acid mine drainage (AMD) in the Luohe River's upper reaches and 63.5%–67.7% in the Yihe River's upper reaches, and about 33% from sewage and industrial effluents in the Luohe River's lower reaches and 27% in Yihe River's lower reaches. Our results confirmed the different anthropogenic impacts on the DHMs concentrations in Luohe River and Yihe River and provided a robust method for DHMs sources appointment and pollution management in river systems.