Isotopic Composition Research Articles

Mixing behaviour and sources of Ag, Pd, and other trace elements in the Estuary and Gulf of St. Lawrence under winter conditions

The marine chemistry of platinum group elements is poorly documented despite robust evidence of their widespread emissions and deposition around the globe. Here, we report the concentrations and discuss the geochemical behaviours of Ag, Pd and other trace and ultra-trace elements in the Estuary and Gulf of St. Lawrence (EGSL). We highlight the contrasting mixing behaviours of these elements, i.e., conservative (Cd, Re) vs. non-conservative (Ag, Pd), in samples collected during the winter and under ice-covered conditions. We ascribe the contrasting geochemical behaviour of these elements to their differential affinity for reactive surfaces carried into the estuary from the frozen watersheds. We also report an increase of the concentrations of Ag (up to 40 pmol L−1), Pd (up to 10 pmol L−1) and Pt (up to 0.4 pmol L−1) in the bottom and oxygen-depleted waters of the Gulf of St. Lawrence (GSL). A strong correlation between dissolved Pt concentrations and the stable carbon isotopic composition of the dissolved inorganic carbon (δ13C-DIC) suggests that the increased mobility of Pt may result from the aerobic mineralization of organic carbon or the oxidation of Pt-bearing organic complexes. Molar Pt/Pd ratios in the three water masses that compose the water column in the EGSL highlight a potential influence of anthropogenic sources near urban centers. The signature of continental end-members will be required to confirm the impacts of road traffic on the estuarine geochemistry of these elements.

Large variability and 2H-depletion of Middle Miocene to Pleistocene alkenone hydrogen isotopes in the Equatorial Pacific reflect subsurface, low light haptophyte growth

Hydrogen isotope ratios of haptophyte derived long-chain alkenones (δ2HC37:2) have shown to be a useful tool for reconstructing past isotopic compositions of surface seawater (δ2HSSW). The δ2HSSW is related to global ice volume, sea surface salinity and the local hydrological cycle. Here, we present a hydrogen isotope record of alkenones spanning the last 14.5 Ma from IODP site U1338 in the east equatorial Pacific. The alkenone-based reconstructed δ2HSSW is substantially more negative and variable than reconstructed δ2HSSW based on published oxygen isotopes of coccolith carbonates. This suggests that factors other than the isotopic composition of seawater affect the hydrogen isotopic composition of alkenones. The relatively negative and highly variable δ2HC37:2 values are in line with published modern observations on alkenones from suspended particulate matter in the equatorial and north Pacific, with the highest values at relatively high light conditions at the surface and the lowest values at higher water depth and relatively low light conditions. This suggests that the relatively negative and highly variable δ2HC37:2 values in these Middle Miocene to Pleistocene sediments are likely derived from haptophytes growing below the sea surface under variable low light conditions. In regions where the contribution of alkenones from subsurface production, due to high subsurface nutrients, at low light intensities to the sediment is relatively high the δ2HC37:2 has to be interpreted with care as a proxy for δ2HSSW.

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.

High-temperature boron partitioning and isotope fractionation between basaltic melt and fluid

In the last two decades, boron has gained significance as a geochemical tracer in mantle studies, particularly related to fluid-mediated processes. In our investigation, we explore how boron and its stable isotopes distribute between basaltic melt and hydrous fluid under conditions relevant to magmatic degassing in the shallow crust (1000–1250 °C, 150–250 MPa). We utilized a synthetic MORB-like composition with added boric-acid isotope standard (NIST-SRM951a) and additional trace elements, subjecting it to varying pressure, temperature, and melt-fluid ratios using an internally heated pressure vessel. The B isotope composition in the quenched glasses were determined through femtosecond laser ablation coupled to a multi-collector inductively-coupled-plasma mass spectrometer. Our experiments revealed that, even at the highest temperatures, boron strongly partitions into the fluid phase, accompanied by significant B isotope fractionation. This leads to an enrichment of the heavy B isotope in the fluid, with a constrained Δ11Bmelt-fluid range of -1.7 ± 0.9‰, consistent with ab-initio modeling results. These findings highlight the potential of B isotopes to trace geochemical processes at elevated temperatures with \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Delta}^{11}{{B}}_{melt-fluid}=2.913-9.693\\frac{{10}^{6}}{{{T}}^{2}}$$\\end{document}. Our results have implications for predicting the δ11B of degassed, water-bearing basaltic magmas and estimating the B isotope composition of their mantle source.

Tracing the geographic origin of Atlantic cod products using stable isotope analysis.

Increasing demand for fish and seafood means that the traceability of marine products is becoming ever more important for consumers, producers and regulators. Highly complex and globalised supply networks create challenges for verifying a stated catch region. Atlantic cod is one of the most commercially important species in the northeast Atlantic. Several regional fisheries supply cod into the trade network, of which some are at greater risk of overexploitation than others. Tools allowing retrospective testing of spatial origin would significantly assist sustainable harvesting of fish, reducing incentives for illegal fishing and fraud. Here, we investigate whether stable isotope ratios of carbon, nitrogen and sulphur can be used to retrospectively identify the catch region of Atlantic cod (Gadus morhua). We measured the isotopic composition of muscle tissue from 377 cod from 10 catch regions across the northeast Atlantic and then applied three different assignment methods to classify cod by region of most likely origin. The assignment method developed was subsequently tested using independently sourced, known-origin samples. Individual cod could be traced back to their true origin with an average assignment accuracy of 70-79% and over 90% accuracy for certain regions. Assignment success rates comparable to those using genetic techniques were achieved when assigning among restricted and pre-selected regions. However, assignment accuracy to the fishery region estimated from independent samples across the whole geographic range of cod averaged ~25% overall, highlighting the need for careful application of isotope-based approaches. Stable isotope techniques can provide effective tools to test for origin in Atlantic cod, but not all catch regions are isotopically distinct. Stable isotopes could be combined with genetic techniques to result in higher assignment accuracy than could be achieved using either method independently. Assignment potential can be estimated from reference datasets, but estimates of realistic assignment accuracy require independently collected data.

A novel pretreatment method for analysis the oxygen isotopic compositions of inorganic phosphorus pools in freshwater sediment

Identifying the sources and cycling of phosphorus (P) is particularly important for formulating effective P management strategies in inland water. The oxygen isotopic compositions of phosphate (δ18OP) are recognized as a promising tool to solve this problem. However, the application of δ18OP in freshwater sediment is currently constrained by multiple difficulties. In this study, we presented a novel pretreatment method for δ18OP analysis of sediment inorganic P pools. Our results showed that the new method has advantages of simple operation, less time-consuming, and high P recovery rates. Specifically, we replaced the traditional Mg-induced co-precipitation (MAGIC) method by introducing Zr-Oxides gels with high selective adsorption function for phosphate. This made subsequent processing simpler and reduced the time consumption to ∼10 days, and the range of P recovery rates were from 88 % to 104 %. Furthermore, we emphasized the necessity of vacuum roasting following lyophilized Ag3PO4 to eliminate residual oxygen-containing impurities (e.g., NO3−, Ag2O, and organic matter). Additionally, evidences from microscopy and spectroscopy confirmed that this method ultimately yielded high-purity Ag3PO4 with the Ag:P molar ratios of 3.35:1. Importantly, combining direct synthesis Ag3PO4 between KH2PO4 and AgNO3 with the Ag3PO4 obtained by the method revealed no stark oxygen isotopic fractionation of phosphate during the pretreatment processes. The newly established δ18OP pretreatment methods here can also be extended to broader studies of the biogeochemical cycling of P in aquatic ecosystems, potentially advancing the understanding of the global P cycle.

High precision determination of carbon isotope composition and concentration of dissolved inorganic carbon in seawaters

Determination of the isotopic composition and concentration of dissolved inorganic carbon (DIC) in sea water requires not only high measurement accuracy, but also the development of unified approaches to data standardization and material collection. In this work, we studied the effect of sampling methods (“in a container” and “in a vial with acid”, with and without the toxin) on the results of determining the values of δ13C(DIC) and the concentration of DIC in sea water. The analytical protocol was described in detail, based on many years of experience in the selection, measurement and standardization of data obtained for a large number of water samples of the Arctic seas. According to this protocol, the values of δ13C(DIC) and [DIC] can be determined with an error of less than 0.05 ‰ (1σ) and 4.5 rel.% respectively. It has been shown that sampling “in a vial with acid” with their storage for 4 months is accompanied by significant contamination by atmospheric carbon dioxide with an underestimation of δ13C(DIC) values by an average of 0.3–0.8 ‰ and an overestimation of [DIC] values by an average of two times. The absence of the toxin that stops biological activity does not lead to significant shifts in the DIC concentration, but it strongly affects the δ13C(DIC) values, which become underestimated by an average of 1 ‰. Using sampling “in a container”, with toxin addition, and following other recommendations, the samples retain the isotope and concentration parameters of DIC for at least year.

Provenance changes of the holocene deposits of Oga and Tsivolki bays (Novaya Zemlya archipelago) according to SR, ND, PB isotope data

The paper is devoted to the Sr-, Nd-, Pb-isotope data obtained for two cores of bottom sediments taken in the Oga and Tsivolki bays of the Severny Island of the Novaya Zemlya archipelago. The studied sequence of sediments from Oga Bay has been accumulated over the last thousand years. The 87Sr/86Sr ratio decreases from top to bottom down the section from 0.72225 to 0.71995, the value of εNd varies from –6.1 to –5.5. The Pb isotopic composition varies within narrow limits: the 206Pb/204Pb ratio from 19.107 to 19.139, the 207Pb/204Pb ratio from 15.632 to 15.635, and the 208Pb/204Pb ratio from 38.568 to 38.635. A rapid decrease in the 87Sr/86Sr ratio at a relatively stable neodymium and lead isotope composition indicates a change in the source of the clastogenic material. This can be explained by the fact that the material of the destruction of Permian clay shales, and then the Devonian-Silurian sedimentary carbonates, first entered the area of glacier abrasion and further, respectively, into the sedimentation zone. The sediment column from the Tsivolki Bay was formed over a little more than 10 thousand years. Based on the Sr, Nd, and Pb isotope ratios, these bottom sediments are divided into lower and upper parts: before and after 150 cm (or ~3500 years). In the lower part of the column, the 87Sr/86Sr ratio increases from 0.72055 to 0.72580, the value of εNd remains approximately the same and varies around –8.2. In the upper part, the 87Sr/86Sr ratio drops to 0.72049 in the near-surface layer; at the same time, the value of εNd increases to –6.4. At the boundary of these two units, the 206Pb/204Pb ratio abruptly changes from about 18.0 in the lower part to 19.3 in the upper part and 208Pb/204Pb from about 36.5 in the lower part to 38.7 in the upper part of the section. The change in the Sr, Nd, and Pb isotope characteristics is likely a reflection of changes in the composition of the rocks in the area where the basin was removed, which is now being eroded by the glacier. Comparison with modern sources supplying clastic material to the Kara Sea showed that the material inputs the Oga and Tsivolki bays only from Novaya Zemlya.

Water-use characteristics of Populus euphratica trees in response to flood and groundwater depth in desert oasis

Populus euphratica, as the dominant species in arid desert area, plays an important role in maintaining the stability of desert ecosystem. However, P. euphratica water-use characteristics at different sizes and the effects of flooding and groundwater depth on water use remain unclear. In this study, the hydrogen and oxygen isotope compositions of xylem water, soil water, and floods were measured and coupled with the MixSIAR model to investigate the water-use patterns of P. euphratica at different sizes, flood periods (before, during, and after floods), and groundwater depths in the Taklimakan Desert hinterland. The carbon isotope composition of P. euphratica leaves was determined to investigate the water-use efficiency (WUE) of P. euphratica. The water-use patterns of P. euphratica at different sizes were consistent because of its reproductive mode (aswxual root tiller reproduction). P. euphratica showed a greater degree of ecological plasticity during different flood periods. Before the flood, the main water sources for P. euphratica were deep-soil-layer (140–220 cm) and near-groundwater-layer (220–300 cm). During the flood, it could absorb the flood directly, reducing water absorption from deep-soil-layer and near-groundwater-layer. After the flood, it resumed water absorption from deep-soil-layer and near-groundwater-layer. P. euphratica water absorption patterns differed at different groundwater depths. In the shallow and middle groundwater depth sample plots, the water sources were the deep-soil and near-groundwater layers, and the population of P. euphratica grew well. In the deep sample plot, water absorption was mainly near the groundwater layer, and the P. euphratica population showed a decreasing trend, further explaining the degradation of P. euphratica in terms of water-use patterns. WUE is related to the growth stage of P. euphratica and the water conditions of the living environment; the more mature the P. euphratica, the more deficit the water conditions, and the higher the WUE. This study provides a basis for maintaining the stability of P. euphratica forests in arid deserts and for water allocation.

Experimental constraints on Mg isotope fractionation during the aragonite–calcite transition and implications for seawater δ26Mg reconstruction

The linkage between the variation of the seawater Mg budget and the long-term carbon cycle can be elucidated by seawater Mg isotope composition (δ26Mg). However, obtaining primary seawater δ26Mg signatures from marine archives is challenging due to the widespread alteration of diagenesis. Aragonite, a common primary marine carbonate, can effectively record seawater δ26Mg but is prone to alteration and transformation into calcite during early diagenesis. Therefore, a comprehensive understanding of Mg isotope behavior during the aragonite–calcite transition is essential to enhance the applicability of aragonite δ26Mg. In this study, we investigate the variation of aragonite δ26Mg during diagenesis with a limited supply of Mg by conducting a series of well-controlled aragonite–calcite transition experiments in a closed system. The experimental conditions encompass temperatures of 60 and 90 °C, the presence of Ca and Na in the solution, varying Na concentrations, as well as the presence of calcite seed. Results demonstrate that the significant decrease of bulk carbonate δ26Mg is accompanied by a substantial amount of Mg released into the solution during the aragonite–calcite transition, and the amount of released Mg is controlled by fluid chemistry via altering Mg partitioning in calcite. Furthermore, Mg isotope fractionation during calcite precipitation is influenced by temperature, ionic strength, and the presence of calcite seed, while kinetics played a negligible role in our experiments. Combined with previous experiments, the temperature-dependent Mg isotope fractionation during calcite precipitation in unseeded experiments is Δ26Mgcal-sol = (−0.13 ± 0.06) × 106/T2 – (0.47 ± 0.68). This fractionation is systematically higher than that of seeded experiments by 0.3–0.6 ‰ from 15 to 90 °C and can mainly be attributed to differences in surface free energy between homogeneous and heterogeneous calcite nucleation. These findings offer fundamental understandings of the Mg isotope behavior during the aragonite–calcite transformation, providing useful insights for interpreting the variation of δ26Mg in experimental and natural carbonates and facilitating ancient seawater δ26Mg reconstruction.

Impactor identification with spallogenic Cr isotopes: The Wabar impact craters (Saudi Arabia)

AbstractPrecise measurements of Cr isotopic composition of terrestrial impactites have successfully provided evidence for the presence of extraterrestrial material and have, in some cases, allowed the identification of the type of impactor responsible for the formation of the impact structure. The high Cr abundance in most meteorite groups aids in detecting extraterrestrial contamination while their distinct isotopic compositions can help with the identification of the nature of the projectile. However, this common approach of detection and identification of extraterrestrial contamination using mass‐independent 53Cr and 54Cr variations fails when the impactor type is an iron meteorite because of their low Cr abundances (which are in a similar range to terrestrial rocks). The present study demonstrates the viability of a spallogenic Cr contribution in iron meteorites (resulting from their long cosmic ray exposure times), which compensates for their low Cr abundances and facilitates the identification of iron‐meteoritic contamination in terrestrial impactites. Thus, it broadens the scope of impactors (and impactites) that can be investigated using mass‐independent Cr isotopes from solely chondrites and primitive achondrites to include iron meteorites. The Wabar impact craters are an optimal candidate for this study, characterized by low weathering, diverse impactites, partial meteorite survival, substantial impactor material contamination, and a felsic target lithology with low background Cr concentration. The Cr isotopic composition of the Wabar background sand, which represents the target lithology, is indistinguishable from the terrestrial Cr isotopic composition range, whereas the Wabar iron meteorites show coupled spallogenic excesses in ε53Cr and ε54Cr. The Cr isotopic compositions of Wabar impactites show resolved deviations from the terrestrial Cr isotopic composition, thereby indicating the presence of Wabar meteoritic contamination. Moreover, the study demonstrates that even an impactor with a non‐carbonaceous chondritic origin, such as a IIIAB iron meteorite, can have a carbonaceous chondrite‐like signature in ε54Cr anomalies due to spallogenic Cr contamination. The study advocates for a comprehensive investigation combining platinum group elements and Cr (and/or Ni, Ru) isotopes to accurately characterize impactor types.

New chloromethane preparation line for the stable chlorine isotope composition analysis*

ABSTRACT Stable isotopes of chlorine have great application potential due to the widespread occurrence of the chlorine anion in water, minerals, living organisms and the environment. In most studies, the chloride ion from the samples is converted to chloromethane, which is then analysed isotopically using a mass spectrometer. In the present study, a new design for a chloromethane preparation line is proposed. In particular, the new chloromethane preparation line uses a new system for injecting iodomethane into the preparation system, as well as ampoules with Teflon valves and the u-shaped freezers. These improvements reduced the preparation time to about 1 h, and also achieved a decent measurement uncertainty of 0.05 permil.

Mascarene basin asthenosphere reservoir source and composition revealed by Central Indian Ridge basalt geochemistry

Along the Central Indian Ridge (CIR), the geochemical and isotopic signature of mid-ocean ridge basalts (MORB) from three segments between 8° and 12°S show a FOZO-like enrichment with elevated 3He/4He (R/RA) (> 10 RA), suggesting small-scale upwelling with a deep primordial mantle component. Based on complementary major and trace elements analysis as well as Sr, Nd and Pb radiogenic isotope compositions of MORB samples from the same location, we confirm the presence of a FOZO/C-like enriched signature characterized by high Pb isotope ratios (206Pb/204Pb = 18.1134–19.1481; 207Pb/204Pb = 15.4710–15.6146 and 208Pb/204Pb = 37.8625–39.0332), relatively low 87Sr/86Sr (0.702767–0.702974) and high 143Nd/144Nd (0.512989–0.513118). In agreement with recent seismological studies highlighting an asthenospheric anomaly centered under the Mascarene Basin and flowing beneath the CIR, we propose that this plume-like anomaly named Mascarene Basin Asthenosphere Reservoir (MBAR) is the source of the enriched FOZO/C-like signature observed along this portion of the CIR. Furthermore, our analyses reveal that the source of the MBAR anomaly may have a unique geochemical signature in the Indian Ocean, distinct from other Indo-African plumes such as the Réunion plume. Moreover, the primordial characteristics, and the location of the MBAR (next to the margin of the African LLSVP) suggest that this plume-like anomaly may be a disconnected blob/proto-plume of a broad mantle structure formed by different Indo-African plumes/upwelling (e.g., Afar and Bouvet plumes) and anchored in the lower mantle.

Hydrologic source identification using stable isotope ratios of bottled drinking water in Egypt

A convenient way to understand hydrologic source identification is to make use of a suitable tracer. Isotopes of oxygen and hydrogen provide that opportunity since the isotope ratios of the primary source, precipitation, can be modified by post precipitation processes. This approach has been tested by carrying out a comprehensive isotope ratios investigation of domestic and imported bottled water sourced and distributed across Egypt. Our collection of bottled water includes 33 samples distributed under 27 distinct brands. We compare the isotope ratios of the bottled water with the isotope ratios of the reported natural water source of this water. The bottled water isotope ratios preserve information about the water sources from which they were derived. The measured oxygen and hydrogen ratios of the studied bottled water samples range from −11.51‰ to 2.94‰, with an average value of −1.89‰ for δ18O and from −81.69‰ to 23.94‰, with an average value of −9.54‰ for δ2H. The observed variability of isotope ratios in the bottled water falls within the span of the natural groundwater resources in Egypt, such as shallow and deep groundwater aquifers as well as claimed non-Egyptian sources. In general, the bottled water samples in the data set can be divided into four distinct groups based on their isotope ratios. One group represents imported bottled water brands, and three groups include domestic brands. The first group represents the imported bottled water brands. Their measured isotopic compositions are similar to those of their claimed sources. The second group has the lowest δ18O and δ2H values and likely originated from the Nubian aquifer. The third and fourth groups appear to have been sourced from the Nile Valley and Delta aquifer. The third group isotopic content and d-excess values indicate a higher degree of mixing with evaporated return flow water. The results provided in this study indicate the diverse hydrogeology of the local bottled water brands. This promises extending the approach to several sites globally.

Mechanistic characterization of dissolved inorganic phosphorus in water during the red tide

The eutrophication of water, such as excessive nitrogen and phosphorus, are closely associated with the outbreak of red tide. However, the response of dissolved inorganic phosphorus (DIP) to red tide remained unclear in water. In this study, three species of diatoms capable of causing red tides were cultured in simulated seawater with different concentrations of DIP. The changes of biomass, chlorophyll a concentration and the carbon stable isotope composition of microalgae, the DIP concentration and pH of the culture medium were compared among the experimental groups. In addition, correlation verification was used to test the correlation between the change of DIP concentration and other indicators. The results showed that in the experimental period, the DIP concentration of each experimental group decreased significantly first, and the concentration dropped to less than 40% of the initial level. After that, the pH of the medium, the biomass, chlorophyll a concentration and carbon stable isotope composition of the microalgae showed varying degrees of increase, and then stabilized or decreased. These also marked the outbreak of red tide. Moreover, the correlation test showed that there was a correlation between them and the change of DIP concentration. Therefore, by exploring the relationship between the change of DIP concentration in water and the occurrence of red tide, this study provides a possible direction for the current prediction of red tide, and provides a basis for further investigation of the occurrence mechanism of red tide.

Mercury compound distribution and stable isotope composition in the different compartments of seabird eggs: The case of three species breeding in East Greenland

Mercury (Hg) is a toxic contaminant of global concern and the impact on Arctic ecosystems, particularly in seabirds, is critical due to large-scale Hg transport towards polar regions and its biomagnification in marine trophic systems. While the adverse effects of Hg on reproductive processes in seabirds are established, the understanding of Hg maternal transfer pathways and their control on Hg reproductive toxicity is limited. The combination of Hg compounds speciation (inorganic mercury and monomethylmercury MMHg) and Hg stable isotope composition in the different egg compartments (yolk, albumen, membrane, and shell) before embryo development was investigated to provide information on (i) Hg maternal transfer mechanisms, (ii) influence of egg biochemical composition on Hg organotropism and (iii) proxies of inputs of Hg contamination. Eggs of three seabird species (the common eider, the black-legged kittiwake and the little auk) collected within the same breeding period (summer 2020) in East Greenland were investigated. For all seabirds, albumen and membrane, the most protein-rich compartments, were the most contaminated (from 1.2 to 2.7 μg g−1 for albumen and from 0.3 to 0.7 μg g−1 for membrane). In these two compartments, more than 82% of the total Hg amount was in the form of MMHg. Additionally, mass-dependent fractionation values (δ202Hg) were higher in albumen and membrane in the three species. This result was mainly due the organotropism of MMHg as influenced by the biochemical properties and chemical binding affinity of these proteinous compartments. Among the different egg compartments, individuals and species, mass-independent fractionation values were comparable (mean ± sd were 0.99 ± 0.11‰, 0.78 ± 0.11‰, 0.03 ± 0.05‰, 0.04 ± 0.10‰ for Δ199Hg, Δ201Hg, Δ200Hg and Δ204Hg, respectively). We conclude that initial MMHg accumulated in the three species originated from Arctic environmental reservoirs exhibiting similar and low photodemethylation extent. This result suggests a unique major source of MMHg in those ecosystems, potentially influenced by sea ice cover.

Post-collisional reworking of juvenile mafic lower crust for the petrogenesis of late Triassic adakitic rocks in the East Kunlun Orogen

The East Kunlun Orogen (EKO), a major component of the Greater Tibetan Plateau, provides an excellent natural laboratory to investigate the tectonic evolution of the Paleo-Tethys Ocean (also known as the A'nyemaqen Ocean in the EKO). We present a combined study of in situ zircon UPb ages and LuHf isotopic compositions, and whole-rock major and trace element and Sr–Nd–Hf isotopic compositions of the post-collisional Xiangjia granodiorite at the eastern end of the EKO. Zircon UPb dating indicates that the Xiangjia granodiorites were emplaced at 225.0–217.1 Ma. Relict zircon cores yield ages of 267.5–239.5 Ma. These granodiorites are calc-alkaline to high-K calc-alkaline and metaluminous to weakly peraluminous, enriched in large-ion lithophile elements and light rare earth elements, and depleted in high field strength elements (e.g., Nb and Ta) and heavy rare earth elements. They yield trace element characteristics that are typical of adakitic rocks, including high Sr (493–590 ppm) and low Yb (0.74–1.12 ppm) and Y (8.83–12.24 ppm) contents, high Sr/Y (40.47–63.64) and (La/Yb)N (11.81–30.91) ratios, and positive Eu anomalies. The UPb ages and Hf isotopic compositions of the relict zircon cores and whole-rock SrNd isotopic compositions of the Xiangjia adakitic rocks are similar to those of the mafic arc magmatic rocks formed during the subduction of the Paleo-Tethys Ocean, suggesting they originated from the reworking of juvenile mafic lower crust. Phase equilibrium modelling suggests that the contemporaneous adakitic rocks from Xiangjia and other areas in the EKO are likely the products of partial melting of the juvenile mafic arc rocks under granulite-facies conditions at 10–11 kbar and 934–951 °C, possibly related to slab break-off in a post-collisional setting.

First-Time Isotopic Characterization of Seleno-Compounds in Biota: A Pilot Study of Selenium Isotopic Composition in Top Predator Seabirds.

This study pioneers the reporting of Se isotopes in marine top predators and represents the most extensive Se isotopic characterization in animals to date. A methodology based on hydride generation─multicollector inductively coupled plasma mass spectrometry─was established for such samples. The study was conducted on various internal organs of giant petrels (Macronectes spp.), encompassing bulk tissues (δ82/78Sebulk), distinct Se-specific fractions such as selenoneine (δ82/78SeSEN), and HgSe nanoparticles (δ82/78SeNPs). The δ82/78Sebulk results (2.0-5.6‰) offer preliminary insights into the fate of Se in key internal organs of seabirds, including the liver, the kidneys, the muscle, and the brain. Notably, the liver of all individuals was enriched in heavier Se isotopes compared to other examined tissues. In nanoparticle fraction, δ82/78Se varies significantly across individuals (δ82/78SeNPs from 0.6 to 5.7‰, n = 8), whereas it exhibits remarkable consistency among tissues and individuals for selenoneine (δ82/78SeSEN, 1.7 ± 0.3‰, n = 8). Significantly, there was a positive correlation between the shift from δ82/78Sebulk to δ82/78SeSEN and the proportion of Se present as selenoneine in the internal organs. This pilot study proves that Se species-specific isotopic composition is a promising tool for a better understanding of Se species fate, sources, and dynamics in animals.

Determination of uranium isotopes in ground water by alpha spectrometry and associated age-dependent ingestion dose.

Determination of uranium isotopes in ground water plays a key role in assessment of geochemical condition of ground water and for estimating ingestion dose received by the general public because of uranium intake through drinking water. An attempt has been made in the present study to estimate isotopic composition and activity ratios (AR) of uranium isotopes by analysing the ground water samples using alpha spectrometry. Associated age-dependent ingestion dose was also calculated for the public of different age groups. 238U, 235U and 234U activity concentration was found to vary in the ranges of 5.85±1.19 to 76.67±4.16, < 0.90 to 3.15±0.84 and 6.52±1.25 to 107.02±4.92 mBq/L, respectively. 235U/238U AR varies from 0.038 to 0.068 with an average of 0.047 which is close to 0.046 implies that uranium in the ground water is from natural origin. Uranium concentration was found to vary in the range of 0.47±0.10μg/L to 6.20±0.34μg/L with a mean value of 3.01±0.23μg/L, which is much lower than national as well as international recommendation value. Annual ingestion dose to the public of all age groups for uranium intake through drinking water ranges from 0.60±0.11 to 19.50±1.03μSv/y.

The marriage between stable isotope ecology and plant metabolomics - new perspectives for metabolic flux analysis and the interpretation of ecological archives.

Even though they share many thematical overlaps, plant metabolomics and stable isotope ecology have been rather separate fields mainly due to different mass spectrometry demands. New high-resolution bioanalytical mass spectrometers are now not only offering high-throughput metabolite identification but are also suitable for compound- and intramolecular position-specific isotope analysis in the natural isotope abundance range. In plant metabolomics, label-free metabolic pathway and metabolic flux analysis might become possible when applying this new technology. This is because changes in the commitment of substrates to particular metabolic pathways and the activation or deactivation of others alter enzyme-specific isotope effects. This leads to differences in intramolecular and compound-specific isotope compositions. In plant isotope ecology, position-specific isotope analysis in plant archives informed by metabolic pathway analysis could be used to reconstruct and separate environmental impacts on complex metabolic processes. A technology-driven linkage between the two disciplines could allow us to extract information on environment-metabolism interaction from plant archives such as tree rings but also within ecosystems. This would contribute to a holistic understanding of how plants react to environmental drivers, thus also providing helpful information on the trajectories of the vegetation under the conditions to come.