Geochimica et Cosmochimica Acta最新文献

{"title":"The role of dissolved sulfide in controlling copper speciation in basaltic melts","authors":"Antonio Lanzirotti, Michelle Muth, Elisabet Head, Matthew Newville, Molly McCanta, Paul J. Wallace, Zoltan Zajacz","doi":"10.1016/j.gca.2025.02.037","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.037","url":null,"abstract":"This study evaluates changes in copper (Cu) speciation that occur in sulfate-dominated basaltic and andesitic magmas equilibrated at oxygen fugacities (<ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>′s) above the nickel-nickel oxide (NNO) buffer. Cu K-edge microfocused X-ray absorption fine structure spectroscopy (XAFS) data are presented from both natural and synthetic silicate glasses. Natural samples analyzed include olivine-hosted melt inclusions from tephra of mafic cinder cones in the Lassen segment of the Cascade arc (USA) and from the Michoacán-Guanajuato volcanic field (Mexico) as representative samples from melts equilibrated at <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> > NNO. A comparison with melts equilibrated at <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> < NNO is provided by analysis of olivine-hosted melt inclusions from Kīlauea Volcano. Data are also presented from copper- and sulfur-bearing synthetic hydrous andesitic glasses synthesized over a range of <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>, from roughly NNO-2 to NNO+2. The Cu spectroscopy data from the natural and synthetic glasses show two dominant Cu species, Cu<ce:sup loc=\"post\">1+</ce:sup> oxides (referred to here as Cu–O) and Cu<ce:sup loc=\"post\">1+</ce:sup> sulfides (referred to here broadly as Cu-S, but not precluding Cu-Fe-S species). The relative proportion of each species present correlates with the relative concentration of dissolved sulfide in the melt. Synthetic sulfur-bearing glasses equilibrated at NNO-1.2 were found to contain exclusively Cu-S species. Sulfur-bearing experimental glasses equilibrated at NNO-0.5 give calculated Cu–O/(Cu–O + Cu-S), defined here as the “Cu–O fraction”, of < 0.10, whereas sulfur-bearing glasses synthesized at NNO+0.6 and NNO+1.8 give calculated Cu–O fraction > 0.96. Natural melt inclusions from Lassen and Kīlauea show a bimodal distribution in Cu–O fraction, with overlapping ranges, of 0.14–0.77 for Lassen and 0.18––0.78 for Kīlauea. Michoacán-Guanajuato inclusions yield Cu–O fractions of 0.68–0.91. The difference in the calculated proportions of Cu–O to Cu-S species appear correlated with available sulfide in the melt. As relative S<ce:sup loc=\"post\">2-</ce:sup> concentrations decrease, the dissolved Cu species in the melt evolves from dominantly Cu-S to Cu–O. This includes melts equilibrated at <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>’s where S<ce:sup loc=\"post\">6+</ce:sup> is the dominant S species. At intermediate sulfide abundances both species appear to coexist. Thermodynamic modeling of the Cu speciation in these silicate glasses suggests that speciation of Cu as a CuFeS<ce:inf loc=\"post\">2</ce:inf> melt species (akin to chalcopyrite or intermediate solid solution) most accurately predicts the measured Cu species. The modeling suggests that a<ce:inf loc=\"post\">FeO</ce:inf> in the silicate melt, <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> and ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"49 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stable isotope equilibria in the dihydrogen-water-methane-ethane-propane system. Part 2: Experimental determination of hydrogen isotopic equilibrium for ethane-H2 from 30 to 200 °C and propane-H2 from 75 to 200 °C","authors":"Andrew C. Turner, Roman Korol, Markus Bill, Daniel A. Stolper","doi":"10.1016/j.gca.2025.02.033","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.033","url":null,"abstract":"The stable isotopic compositions of light <ce:italic>n</ce:italic>-alkanes, including methane, ethane, and propane, are often used to identify the sources and thermal maturity of natural gas samples. Though stable isotopic compositions of these molecules are commonly assumed to be controlled by kinetic isotope effects, recent studies have proposed both carbon and hydrogen isotopic equilibrium may also occur in some samples. Assessing whether samples are in isotopic equilibrium requires knowledge of light alkane equilibrium fractionation factors over geologically relevant temperatures for formation and storage (up to ∼300 °C). In this study, we report experimental results of hydrogen isotopic equilibrium between ethane and H<ce:inf loc=\"post\">2</ce:inf> from 30 to 200 °C and propane and H<ce:inf loc=\"post\">2</ce:inf> from 75 to 200 °C. We compare these results with high-level theoretical calculations and provide a preferred polynomial fit to describe equilibrium fractionation factors. Comparison of these fractionation factors with a compilation of ∼500 compiled environmental gas samples supports the proposal that many (∼50%) of these natural gas samples exhibit hydrogen isotopic compositions consistent with having formed in or attained methane-ethane-propane hydrogen isotopic equilibrium over geologically relevant temperatures for formation and storage (50–300 °C).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The overlooked role of mineral pore geometry in the solid-solution partitioning of (poly)oxyanionic metals","authors":"Yu Dai, Benjamin C. Bostick, Huihui Du, Xueyuan Gu, Guopei Huang, Shirong Liu, Lei Song, Yizhang Liu, Zengping Ning, Jing Sun, Chengshuai Liu","doi":"10.1016/j.gca.2025.02.031","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.031","url":null,"abstract":"A high specific surface area (SSA) typically signifies a superior adsorption capacity. Nevertheless, minerals with high SSAs tend to possess tiny pores that may not be accessible to relatively large (poly)oxyanionic metals. Herein, we assessed the adsorption of (poly)oxyanionic metals on 2-line and 6-line ferrihydrite and goethite with distinct SSAs and pore geometries. SSA was estimated by BET isotherm using N<ce:inf loc=\"post\">2</ce:inf>, while pore geometry was measured by N<ce:inf loc=\"post\">2</ce:inf> adsorption isotherms and positron annihilation lifetime spectroscopy. Tungstate and its polymers were chosen as representative (poly)oxyanions. Adsorption experiments were performed with constant mineral surface area, but different contact time, pH, and tungsten concentrations. Unexpectedly, the Langmuir adsorption capacities per unit surface area on 6-line ferrihydrite and goethite were 2–6 and 3–11 times as high as those on 2-line ferrihydrite, respectively. Adsorption on 2-line ferrihydrite was also severely kinetically limited. The varying rates and magnitudes of adsorption were attributed to distinct mineral pore widths: (poly)tungstates could hardly fit within the abundant tiny pores in 2-line ferrihydrite formed by voids between the primary particles/aggregates, but could enter the larger pores in 6-line ferrihydrite and goethite. Consequently, significant decreases of mineral microporosity (&lt;2 nm) were observed following (poly)tungstate adsorption. Tungstate and polytungstate with different hydrated ion radii exhibited similar adsorption behavior, most likely due to the formation of adsorbed polytungstate directly on mineral surface. Our data demonstrate that mineral pore geometry controls the solid-solution partitioning of (poly)oxyanionic metals, which is crucial to comprehend their environmental fate and to mitigate their contamination.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"154 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural transformation of manganese oxides induced by the oxidation of As(III) and Mn(II)","authors":"Huan Liu, Xiangjie Cui, Xiancai Lu, Elaine D. Flynn, Jeffrey G. Catalano","doi":"10.1016/j.gca.2025.02.034","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.034","url":null,"abstract":"Manganese (Mn) oxides are ubiquitous in natural systems, occurring as reactive nanoparticles with high surface area that play key roles in controlling the fate of trace elements and contaminants. These minerals may effectively scavenge arsenite [As(III)] from solution via oxidation and adsorption reactions, generating solid-phase Mn(II/III) as well as dissolved Mn(II). At redox interfaces, dissolved Mn(II) similarly generates solid-phase Mn(II/III) via adsorption and comproportionation reactions with Mn oxides, inducing structural transformations. It is unclear how the co-reaction of As(III) and Mn(II) with Mn oxides at redox interfaces affects both arsenic oxidation and mineral structure. This study investigates the reaction of As(III) and δ-MnO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;, a phyllomanganate mineral that has a turbostratic structure similar to natural biogenic Mn oxides, at pH 4, 7, and 8.5. Dissolved Mn(II) is introduced in some systems to investigate the synergistic and competitive effects of its co-reaction with As(III) on the structure of Mn oxides. Results show that partial adsorption of dissolved As after 2 d, with all remaining dissolved As being oxidized to As(V). The adsorption of As increased with decreasing pH. As(III) was fully oxidized to As(V) in the solid phase, and thus also the system, regardless of pH and dissolved Mn(II) concentration. Adsorbed As(V) occurred as a bidentate, binuclear surface complex with a coordination geometry unaffected by chemical conditions. Reactions of As(III) and Mn(II) with δ-MnO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; each decreased the average manganese oxidation state of the mineral. When these co-occurred, their effects were largely additive. Both Mn(II) and Mn(III) were generated in the solid phase, with a greater relative proportion of Mn(III) at higher pH. Mn(II) induced a partial transformation of δ-MnO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; to nsutite at pH 4, but this was inhibited by As(III) despite being similar to the greater generation of solid-phase Mn(II/III). At pH 7, the reaction with Mn(II) increased layer stacking, with a lesser increase from reaction with As(III) and weak to no change in stacking when dissolved As(III) and Mn(II) initially co-occurred. In contrast, at pH 8.5, reaction with As(III) induced greater layer stacking than dissolved Mn(II), which had little effect, and As(III) and Mn(II) co-existence produced even stronger stacking and initiated a partial conversion of the sheet symmetry from hexagonal to orthogonal. Co-addition of dissolved As(V) and Mn(II) had similar effects as a mixture of dissolved As(III) and Mn(II) at pH 4 and 7 but caused a complete inhibition of structural changes at pH 8.5. This study indicates that the effects of the co-existence of Mn(II) and As(III) on the transformation of Mn oxides are pH-dependent, showing an inhibitory effect at acidic and neutral pH while a synergistic effect under alkaline conditions. This study also suggests that As(III) could act as an ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"198 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666348","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithium isotope evidence shows Devonian afforestation may have significantly altered the global silicate weathering regime","authors":"Xianyi Liu, Alexander J. Krause, David J. Wilson, Wesley T. Fraser, Michael M. Joachimski, Uwe Brand, Alycia L. Stigall, Wenkun Qie, Bo Chen, Xiangrong Yang, Philip A.E. Pogge von Strandmann","doi":"10.1016/j.gca.2025.02.036","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.036","url":null,"abstract":"The Devonian Period (∼359–419 Ma) documents significant environmental changes and marine species turnover, but whether these changes were linked to terrestrial weathering remains unknown. Here, we use lithium isotopes in brachiopods and bulk marine carbonates (δ<ce:sup loc=\"post\">7</ce:sup>Li<ce:inf loc=\"post\">carb</ce:inf>) from the Devonian Period to investigate changes in silicate weathering, which represents the primary long-term atmospheric CO<ce:inf loc=\"post\">2</ce:inf> sink. A rise of ∼ 10 ‰ in δ<ce:sup loc=\"post\">7</ce:sup>Li<ce:inf loc=\"post\">carb</ce:inf> values (from ∼ 8 ‰ to ∼ 18 ‰) is observed across the Mid-Devonian (∼378–385 Ma), suggesting a major change in the seawater Li cycle. We attribute the rise in δ<ce:sup loc=\"post\">7</ce:sup>Li<ce:inf loc=\"post\">carb</ce:inf> values to an increase in the dissolved riverine Li flux and δ<ce:sup loc=\"post\">7</ce:sup>Li<ce:inf loc=\"post\">river</ce:inf> values, which likely arose from increases in both weathering intensity and regolith thickness, related to the expansion of deep-rooted plants. However, the presence of such terrestrial ecosystems would also have restricted the continuous weathering of silicate rocks. In order to maintain high δ<ce:sup loc=\"post\">7</ce:sup>Li<ce:inf loc=\"post\">seawater</ce:inf> values in the Late Devonian, we propose that repeated cycles of destruction and regeneration of terrestrial forest ecosystems could have occurred, which would have prevented a supply-limited weathering regime from being permanently established. Such a process would potentially have caused oscillations in marine nutrient availability and redox conditions, thereby contributing to prolonged marine biodiversity loss during the Late Devonian.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of clay mineral on bacteria–virus interactions and the fate of microbial biomass carbon","authors":"Xiaowen Zhang, Haina Wang, Yan Liu, Hailiang Dong","doi":"10.1016/j.gca.2025.02.030","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.030","url":null,"abstract":"Viruses are the major drivers of global geochemical cycles through lysis of host bacteria. The release of cellular organic matter (OM) to the environment via viral lysis short-circuits the carbon flow from bacteria to higher trophic levels, a process known as the “viral shunt”. However, current understanding of bacteria–virus interactions is limited to the oceans. In sediments and soils, clay minerals are ubiquitous, but their roles in controlling viral lysis of host bacteria are virtually unknown. Here, we established a model experimental system using clay mineral montmorillonite, a common bacterium <ce:italic>Shewanella oneidensis</ce:italic> MR-1, and its lytic virus MSO-5 to investigate the impacts of clay mineral on bacteria–virus interactions, as well as the fate of the released OM. X-Ray Diffraction (XRD) and pyrolysis gas chromatography-mass spectrum (PY-GC–MS) were used to detect OM intercalation into montmorillonite interlayer. The results showed that the presence of montmorillonite delayed lysis of bacterial host due to its spatial separation from virus and delayed release of dissolved organic matter (DOM) through adsorption. Low molecular weight compounds released from virus-induced cell lysis, mainly benzene derivatives, N-containing compounds, and ketones were preferentially intercalated into the interlayer space of montmorillonite. Our results demonstrate that clay minerals play an important role in bacteria–virus interactions in controlling release and preservation of microbially-derived organic matter, which is expected to have an increasingly important impact on carbon cycling as sediment inflow increases with global warming. This study advances our understanding of mineral–bacteria–virus interactions in the viral shunt, especially in clay-rich environments such as soils and sediments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"92 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental determination of hydrogen isotopic equilibrium in the system H2O(l)-H2(g) from 3 to 90 °C","authors":"Flora Hochscheid, Andrew C. Turner, Noam Lotem, Markus Bill, Daniel A. Stolper","doi":"10.1016/j.gca.2025.02.029","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.029","url":null,"abstract":"Molecular hydrogen (H<ce:inf loc=\"post\">2</ce:inf>) is found in a variety of settings on and in the Earth from low-temperature sediments to hydrothermal vents, and is actively being considered as an energy resource for the transition to a green energy future. The hydrogen isotopic composition of H<ce:inf loc=\"post\">2</ce:inf>, given as D/H ratios or δD, varies in nature by hundreds of per mil from ∼−800 ‰ in hydrothermal and sedimentary systems to ∼+450 ‰ in the stratosphere. This range reflects a variety of processes, including kinetic isotope effects associated with formation and destruction and equilibration with water, the latter proceeding at fast (order year) timescales at low temperatures (&lt;100 °C). At isotopic equilibrium, the D/H fractionation factor between liquid water and hydrogen (<ce:sup loc=\"post\">D</ce:sup>α<ce:inf loc=\"post\">H2O(l)-H2(g)</ce:inf>) is a function of temperature and can thus be used as a geothermometer for H<ce:inf loc=\"post\">2</ce:inf> formation or re-equilibration temperatures. Multiple studies have produced theoretical calculations for hydrogen isotopic equilibrium between H<ce:inf loc=\"post\">2</ce:inf> and water vapor. However, only three published experimental calibrations used in geochemistry exist for the H<ce:inf loc=\"post\">2</ce:inf>O-H<ce:inf loc=\"post\">2</ce:inf> system: two between 51 and 742 °C for H<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">(g)</ce:inf>-H<ce:inf loc=\"post\">2(g)</ce:inf> (<ce:cross-refs ref>Suess, 1949; Cerrai et al., 1954</ce:cross-refs>), and one in the H<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">(l)</ce:inf>-H<ce:inf loc=\"post\">2(g)</ce:inf> system for temperatures &lt;100 °C (<ce:cross-ref ref>Rolston et al., 1976</ce:cross-ref>). Despite these calibrations existing, there is uncertainty on their accuracy at low temperatures (&lt;100 °C; e.g., <ce:cross-ref ref>Horibe and Craig, 1995</ce:cross-ref>).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"61 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stable isotope equilibria in the dihydrogen-water-methane-ethane-propane system. Part 1: Path-integral calculations with CCSD(T) quality potentials","authors":"Roman Korol, Andrew C. Turner, Apurba Nandi, Joel M. Bowman, William A. Goddard III, Daniel A. Stolper","doi":"10.1016/j.gca.2025.02.028","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.028","url":null,"abstract":"Isotopic compositions of alkanes are typically assumed to be kinetically controlled, but recently it has been proposed that alkanes can isotopically equilibrate for both C and H isotopes during natural gas generation. Evaluation of this requires knowledge of the isotopic equilibrium between alkanes and other common hydrogen and carbon bearing species. Here we calculate isotopic equilibria within and between gaseous dihydrogen (H<ce:inf loc=\"post\">2</ce:inf>), water (H<ce:inf loc=\"post\">2</ce:inf>O), methane (CH<ce:inf loc=\"post\">4</ce:inf>), ethane (C<ce:inf loc=\"post\">2</ce:inf>H<ce:inf loc=\"post\">6</ce:inf>) and propane (C<ce:inf loc=\"post\">3</ce:inf>H<ce:inf loc=\"post\">8</ce:inf>), including isotope fractionation among molecules, clumped isotope effects, as well as among sites of propane (i.e., the site-specific isotope effects) from 0°C to 500°C using a path-integral method paired with high-level descriptions of molecular potentials and the diagonal correction to the Born–Oppenheimer approximation. While path-integral calculations with high-level CCSD(T) potentials are available for the isotopic equilibria involving methane, the path-integral calculations for ethane and propane have only been performed based on lower-level descriptions of the molecular potentials. We analyze the relative importance of various approximations that are commonly employed when isotopic equilibria are evaluated. We find that clumped isotope effects can be calculated to the same accuracy using computationally inexpensive combination of the Bigeleisen-Mayer-Urey model with the molecular potential from density functional theory. In contrast, fractionation and site preferences of both deuterium and carbon-13 benefit from the use of the higher level CCSD(T) potentials and accounting for anharmonic effects. Additionally, for fractionation and site preference of deuterium, corrections to Born–Oppenheimer approximation can also be important.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"56 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dry season dominance of salinity’s impact on hydrogen isotope fractionation in Aegiceras corniculatum mangrove lipids","authors":"Yao-Ping Wang, Zhiguang Song, Jia Xia, Zhao-Wen Zhan, Alex L. Sessions, Shaelyn N. Silverman, Yuan Gao, Guopeng Li, Ding He","doi":"10.1016/j.gca.2025.02.024","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.024","url":null,"abstract":"The hydrogen isotope ratios (δ&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;H) of mangrove leaf waxes are influenced by both precipitation and water salinity, making them promising proxies for paleohydrologic and paleosalinity reconstructions. However, the mechanism by which salinity affects &lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;H/&lt;ce:sup loc=\"post\"&gt;1&lt;/ce:sup&gt;H fractionation remain unclear. While previous studies have shown that fractionation between source and leaf water pools is not the primary driver, it is still uncertain how biosynthetic isotope fractionation contributes to this process and how these effects vary across different seasons. To our knowledge, no studies have directly compared the seasonal variations in isotope fractionation between the dry and wet seasons, which are characteristic of tropical and subtropical regions. To address these questions, we measured δ&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;H values of &lt;ce:italic&gt;n&lt;/ce:italic&gt;-alkanes and &lt;ce:italic&gt;n&lt;/ce:italic&gt;-fatty acids in the leaves of &lt;ce:italic&gt;Aegiceras corniculatum&lt;/ce:italic&gt; collected from the Zhanjiang estuary during both the dry and wet seasons. We compared these data with δ&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;H and δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values from leaf water, xylem water, estuary surface water, and sediment pore water to discern potential differences in isotopic fractionation mechanisms. Our findings indicate that net &lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;H/&lt;ce:sup loc=\"post\"&gt;1&lt;/ce:sup&gt;H fractionation increases with salinity for both C&lt;ce:inf loc=\"post\"&gt;31&lt;/ce:inf&gt;&lt;ce:italic&gt;n&lt;/ce:italic&gt;-alkanes (2.5 ± 0.9 ‰ ppt&lt;ce:sup loc=\"post\"&gt;−1&lt;/ce:sup&gt;) and C&lt;ce:inf loc=\"post\"&gt;16:0&lt;/ce:inf&gt;&lt;ce:italic&gt;n&lt;/ce:italic&gt;-fatty acids (1.0 ± 0.2 ‰ ppt&lt;ce:sup loc=\"post\"&gt;−1&lt;/ce:sup&gt;) during the dry season, whereas no similar such trends were observed in the wet season. These seasonal variations highlight the dominant impact of salinity on hydrogen isotope fractionation in &lt;ce:italic&gt;A. corniculatum&lt;/ce:italic&gt; lipids during the dry season. We also found that salinity-driven fractionation is not solely related to water uptake but rather to physiological responses to high salinity. This finding aligns with previous studies, which indicate that salinity-induced effects on hydrogen isotopic fractionation are primarily driven by physiological adaptations, rather than by salinity-dependent fractionation mechanisms in leaf and xylem water. Building upon this understanding, we propose novel hypotheses: heightened salinity in the dry season reduces photosynthetic efficiency in &lt;ce:italic&gt;A. corniculatum&lt;/ce:italic&gt; due to limited CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; availability, which in turn triggers increased production of compatible solutes. This may reduce cellular water availability and limit isotopic exchange. Additionally, elevated salinity could intensify carbon metabolism, affecting the residence time of intermediates in the TCA cycle and influencing isotopic water exchange. While we propose these as potential mechanisms, ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"22 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microbial-mediated bastnaesite dissolution as a viable source of clay-adsorbed rare earth elements in the regolith-hosted deposits","authors":"Yilin He ,&nbsp;Lingya Ma ,&nbsp;Xurui Li ,&nbsp;Xun Liu ,&nbsp;Xiaoliang Liang ,&nbsp;Jianxi Zhu ,&nbsp;Hongping He","doi":"10.1016/j.gca.2025.02.027","DOIUrl":"10.1016/j.gca.2025.02.027","url":null,"abstract":"<div><div>Understanding the weathering processes of minerals containing rare earth elements (REE) is crucial for unraveling the genesis of regolith-hosted REE deposits. However, the weathering mechanisms of bastnaesite, a primary REE carrier in parent rocks, remain uncertain. Discrepancies between field observations and thermodynamic calculations regarding its weatherability during mineral-groundwater interactions have raised questions about the factors controlling the natural weathering of bastnaesite. Here, we propose that microbial activities significantly contribute to the dissolution of bastnaesite. To test this hypothesis, we conducted bio-weathering experiments using natural bastnaesite and a wild strain, <em>Bacillus thuringiensis</em> (Bt) isolated from regolith-hosted REE deposits. The results indicate that, consistent with thermodynamic predictions, bastnaesite exhibited resistance to dissolution under simulated groundwater pH conditions (∼6). However, the presence of Bt significantly enhanced bastnaesite dissolution. Bt exuded various types of organic acids, acidifying the solution during bio-weathering. Comparative biotic and abiotic experiments demonstrated that Bt could induce bastnaesite dissolution through acidolysis and ligand complexation. These effects were further strengthened by direct cell attachment to the mineral surfaces. Existing field studies suggest the rapid dissolution of bastnaesite during the very early rock weathering period, adding uncertainty about the contribution of bastnaesite to the enrichment of clay-adsorbed REE. Our results indicate that the dissolution of bastnaesite is largely pH-dependent, with bio-dissolution rates (R_Ce = 10⁻¹³ − 10⁻¹² mol·m⁻²·s⁻¹) close to or slightly lower than the lab-determined dissolution rates of feldspars and micas at weakly acidic to neutral pH levels. Since the weathering of these aluminosilicate minerals provides the dominant source of clay minerals, we infer that some REE released from bastnaesite can be retained by clay minerals in the weathering profile. These findings may provide new insights into the natural weathering of bastnaesite and advance our understanding of the REE biogeochemical cycling during the formation of regolith-hosted REE deposits.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 43-52"},"PeriodicalIF":4.5,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143577256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}