Geochimica et Cosmochimica Acta最新文献

{"title":"Equilibrium thermodynamics of K-Na exchange between alkali feldspars and aqueous alkali chlorides at 450 °C and 427 bar (0.31 g cm−3 water density)","authors":"Taraneh Roodpeyma, Thomas Driesner, Corey Archer","doi":"10.1016/j.gca.2026.01.035","DOIUrl":"10.1016/j.gca.2026.01.035","url":null,"abstract":"<div><div>K-Na exchange between alkali feldspars and aqueous KCl and NaCl is an important process in many natural hydrothermal systems and proceeds according to the reaction:</div><div><span><math><mrow><mi>K</mi><mi>A</mi><mi>l</mi><msub><mrow><mi>S</mi><mi>i</mi></mrow><mn>3</mn></msub><msub><mi>O</mi><mn>8</mn></msub><mfenced><mrow><mi>s</mi></mrow></mfenced><mo>+</mo><mi>N</mi><mi>a</mi><mi>C</mi><mi>l</mi><mspace></mspace><mrow><mo>(</mo><mi>a</mi><mi>q</mi><mo>)</mo></mrow><mo>↔</mo><mi>N</mi><mi>a</mi><mi>A</mi><mi>l</mi><msub><mrow><mi>S</mi><mi>i</mi></mrow><mn>3</mn></msub><msub><mi>O</mi><mn>8</mn></msub><mfenced><mrow><mi>s</mi></mrow></mfenced><mo>+</mo><mi>K</mi><mi>C</mi><mi>l</mi><mrow><mo>(</mo><mi>a</mi><mi>q</mi><mo>)</mo></mrow></mrow></math></span></div><div>Existing experimental calibrations of the equilibrium constant display inconsistencies and in some cases have relied on ambiguous assumptions such as deriving it from experiments with concentrated solutions without accounting for activity coefficients. In order to test the validity of these previous approaches, we conducted an equilibrium experiment at 450 °C and 427 bars (equivalent to a pure water density of 0.31 g cm<sup>−3</sup>) for 16 different alkali chloride molalities ranging from 13 m down to 10<sup>-4</sup> m, each with three different starting compositions to approach equilibrium from different sides. At the lowest concentrations, the aqueous electrolyte activity coefficients appear to approach unity such that we can derive a revised aqueous equilibrium K/Na mole ratio of 0.039 ± 0.001 at infinite dilution and an equilibrium constant of 0.044 ± 0.002, much lower than the previous literature value of 0.170–0.173. Using the revised value, we calculate how the KCl/NaCl activity coefficient ratio changes with chloride concentration. The bulk activity coefficient of KCl is up to 5 times lower than that of NaCl, in contrast to the commonly made assumption of equality to NaCl as the dominant solute. An analysis in terms of the predictive <span><math><msub><mi>b</mi><mi>γ</mi></msub></math></span> activity model shows that for the most commonly used parameters and assumptions, the Debye-Hückel contribution to the KCl/NaCl activity coefficient ratio predicts the wrong sign. Using such an analysis, the empirical <span><math><msub><mi>b</mi><mi>γ</mi></msub></math></span> term would no longer be a minor correction or, alternatively, non-unity activity of the neutral ion pairs would have to account for a significant fraction of the needed correction. Another possibly important reason for the dominance of the correction term(s) is that at our nominally supercritical experimental conditions the standard state would refer to the electrolyte in water of vapor-like density while the more concentrated solutions display liquid-like behavior.</div><div>As additional result, we provide two lines of evidence that for certain concentrations the alkali feldspar-equilibrated fluid is ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 219-232"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146071695","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":"Using carbonate Zn and conodont Sr isotopes to link marine productivity and chemical weathering intensity changes during the Permian-Triassic transition","authors":"He Zhao ,&nbsp;Thomas J. Algeo ,&nbsp;Xiangdong Wang ,&nbsp;Zhengyi Lyu ,&nbsp;Xueqian Feng ,&nbsp;Xinyang Yao ,&nbsp;Zhenfeng Luo ,&nbsp;Zhaochu Hu","doi":"10.1016/j.gca.2026.03.027","DOIUrl":"10.1016/j.gca.2026.03.027","url":null,"abstract":"<div><div>The end-Permian mass extinction (EPME), the greatest biodiversity crisis since the Cambrian Explosion, was followed by a protracted and complex recovery. Intensified continental weathering and fluctuating primary productivity, under conditions of hyperwarming, characterized both the EPME and the subsequent protracted marine biotic recovery. However, detailed reconstructions of changes in weathering and productivity during the Permian-Triassic transition have not been achieved yet, leaving uncertainty regarding the nature of environmental controls during the extinction and recovery intervals. To address this issue, we apply a novel multi-proxy framework centered on the coupled use of carbonate zinc (δ⁶⁶Zn_carb) and conodont strontium (⁸⁷Sr/⁸⁶Sr_conodont) isotopes. We investigate the environmental sensitivity of this paired system using a high-resolution dataset from the Guryul Ravine section (Indian Kashmir), integrating δ⁶⁶Zn_carb, ⁸⁷Sr/⁸⁶Sr_conodont, δ¹³C_org, and bulk-rock geochemistry across the Permian-Triassic boundary. Elevated chemical index of alteration (CIA) and ⁸⁷Sr/⁸⁶Sr_conodont values in the uppermost Permian record enhanced weathering that likely boosted marine productivity and caused anoxia. Elevated δ⁶⁶Zn_carb coupled with declining ⁸⁷Sr/⁸⁶Sr_conodont in the lowermost Triassic (<em>H. parvus</em> Zone) suggests reduced weathering inputs following the EPME. A subsequent rapid ⁸⁷Sr/⁸⁶Sr rise (above <em>I. staeschei</em> Zone) marks renewed weathering and nutrient input, driving high productivity (high δ⁶⁶Zn_carb, positive δ¹³C_org) and a second anoxic episode. A negative excursion in δ⁶⁶Zn_carb coupled with rising ⁸⁷Sr/⁸⁶Sr_conodont at the Griesbachian-Dienerian boundary indicates strong weathering but low marine productivity. The amelioration of nutrient limitations during the Dienerian, indicated by a positive δ⁶⁶Zn_carb excursion, was potentially driven by declining seawater temperatures and weakened oceanic anoxia. This study establishes the Zn-Sr isotope pair as a robust tracer for deconvolving weathering-productivity dynamics and demonstrates the close relationships between global climate, weathering fluxes, and ocean-redox conditions that were pivotal in driving the EPME and shaping the subsequent Early Triassic marine biotic recovery. In particular, our findings reveal the Dienerian to have been a transient phase of environmental and ecological amelioration during the Early Triassic, setting the stage for the subsequent development of complex Mesozoic marine ecosystems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 418-432"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465060","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 importance of dissolved sulfhydryl binding sites on the speciation of aqueous metals in lake waters: Results from pristine and human-impacted lakes","authors":"Jessica C. Brown,&nbsp;Qiang Yu,&nbsp;Antonio Simonetti,&nbsp;Jeremy B. Fein","doi":"10.1016/j.gca.2026.03.026","DOIUrl":"10.1016/j.gca.2026.03.026","url":null,"abstract":"<div><div>Sulfhydryl binding sites (R-SH) are ubiquitous on dissolved organic molecules in natural aqueous environments, within complex solid organic frameworks, and on microbial cell walls. Although their concentrations are typically lower than that of other ligands, sulfhydryl binding sites likely play an outsized role in metal binding due to their high affinity to bind chalcophile elements. Few studies have measured sulfhydryl concentrations in natural environmental samples due to the difficulty, until recently, of measuring total sulfhydryl concentrations on solids or in aqueous samples, and none have quantified the impact that these binding sites have on metal speciation. In this study, recent advances in measuring dissolved total sulfhydryl site concentrations were applied to a set of water samples from pristine and human-impacted lakes to determine the role of dissolved sulfhydryl binding sites in metal speciation in each lake. In addition to reporting sulfhydryl site concentrations in each sample, we also measured the pH, dissolved organic carbon concentration, the total dissolved concentrations of a wide range of elements and anions, and the total dissolved binding site concentrations. Chemical analyses were used in conjunction with Visual MINTEQ to model the speciation of the dissolved elements in each lake sample. Measurable sulfhydryl concentrations were recorded in all lake samples, with significantly greater sulfhydryl concentrations in the pristine compared to the human-impacted lakes. Speciation modeling indicates that aqueous element-sulfhydryl complexes represent a significant proportion of the total dissolved element budget for a range of elements in both the natural and human-impacted lakes, with greater proportions observed in the pristine lake samples. For example, modeling results indicate that the pristine lake waters have an average of 47% of the total dissolved Zn present in solution as an aqueous Zn-sulfhydryl complex compared to a lower average of 29% for human-impacted lakes. Overall, the results of this study demonstrate that it is imperative to measure at least total aqueous sulfhydryl site concentrations in environmental aqueous samples in order to accurately model dissolved element speciation in those waters and thereby to assess and model contaminant mobility and bioavailability.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 233-249"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465062","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":"Labile Fe(III) species control arsenic adsorption and oxidation during magnetite-solution interactions under anoxic conditions","authors":"Xinyue Yu ,&nbsp;Di Wu ,&nbsp;Wan Cheng ,&nbsp;Yuefei Ding ,&nbsp;Xiaoxu Li ,&nbsp;Jing Chen ,&nbsp;Xiaohui Wu ,&nbsp;Xin Zhang ,&nbsp;Juan Liu ,&nbsp;Linling Wang ,&nbsp;Anxu Sheng ,&nbsp;Kevin M. Rosso","doi":"10.1016/j.gca.2026.03.041","DOIUrl":"10.1016/j.gca.2026.03.041","url":null,"abstract":"<div><div>Interfacial electron transfer (IET) between aqueous Fe(II) (Fe(II)_aq) and iron (oxyhydr)oxides is a widespread process that generates highly reactive Fe(III) species (Fe(III)_labile), facilitating rapid mineral recrystallization into stable crystalline phases. These systems are known to be more reducing towards a wide variety of electron accepting species. However, these same systems show anomalous redox reactivity toward arsenic, in that they favor oxidation of As(III) rather than reduction of As(V). We hypothesized this reactivity arises from a direct quantitative connection between Fe(III)_labile production and As(III) oxidation. Here we tested this hypothesis by employing magnetite nanoparticles with varying stoichiometries (Fe(II)/Fe(III) ratios), denoted Mt_0.48, Mt_0.37, and Mt_0.24, as representative minerals that, along with varying Fe(II)_aq amendment, were used to manipulate Fe(III)_labile generation and establish its role in reactions with As(III) and As(V). Magnetite could generate Fe(III)_labile through dual pathways of Fe(II)_aq release and adsorption, driven by reversible electron redistribution across the magnetite-solution interface. At pH 7.0 and 20–100 µM arsenic, the adsorption rates and capacities for both As(III) and As(V), as well as As(III) oxidation extents, followed the order Mt_0.48 &gt; Mt_0.37 &gt; Mt_0.24, despite the lower apparent redox potentials of more stoichiometric particles. These reactions were accompanied by extensive depletion of Fe(III)_labile, showing a strong global linear correlation between Fe(III)_labile consumption and As(III) oxidation across all systems. DFT calculations further revealed the strong electronic interactions and substantial Bader charge transfer (1.943–2.212 <em>e</em>) from As(III) to Fe(III)_labile. Our results identify Fe(III)_labile as the critical redox-active species controlling arsenic adsorption and As(III) oxidation on magnetite nanoparticles, providing new mechanistic insights into the role of this important species and coupled arsenic-iron cycling in subsurface environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 308-319"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587133","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":"Trace element partitioning during water-saturated eclogite melting at 3 GPa under variable oxygen fugacity – Implications for subduction zone magmatism","authors":"Alexandre Corgne ,&nbsp;Gaëlle Plissart ,&nbsp;Julien Siebert ,&nbsp;Jessica Langlade ,&nbsp;Christèle Guivel ,&nbsp;José Joaquín Figueroa Ruíz ,&nbsp;Joaquín Catalan ,&nbsp;Manuel Enrique Schilling","doi":"10.1016/j.gca.2026.03.046","DOIUrl":"10.1016/j.gca.2026.03.046","url":null,"abstract":"&lt;div&gt;&lt;div&gt;To shed light on the composition of partial melts of subducted oceanic crust potentially produced at subarc depths and constrain the contribution of this particular melting process to arc magmatism, we performed melting experiments of an eclogite source at relevant conditions (3 GPa, 800–950 °C and oxygen fugacity from ∼FMQ+3 to FMQ-3) and produced new partition coefficients (D) for many trace elements between eclogite minerals and hydrous rhyolitic melts. Our results show that lattice strain control on partitioning is significant, as evidenced by a near-parabolic dependence of log D to the ionic radius for trivalent cations entering the large sites of both garnet and clinopyroxene. The partition coefficients of some trace elements also display significant dependences on temperature and oxygen fugacity. D&lt;sub&gt;Sc&lt;/sub&gt;, D&lt;sub&gt;Y&lt;/sub&gt;, D&lt;sub&gt;Hf&lt;/sub&gt;, D&lt;sub&gt;Zr&lt;/sub&gt;, D&lt;sub&gt;Th&lt;/sub&gt; and D&lt;sub&gt;Ce&lt;/sub&gt; decrease with increasing temperature for both garnet-melt and clinopyroxene-melt partitioning. With increasing temperature, D&lt;sup&gt;Grt-Liq&lt;/sup&gt;&lt;sub&gt;REE&lt;/sub&gt; tends to decrease, while D&lt;sup&gt;Cpx-Liq&lt;/sup&gt;&lt;sub&gt;Ba&lt;/sub&gt; and D&lt;sup&gt;Cpx-Liq&lt;/sup&gt;&lt;sub&gt;Sr&lt;/sub&gt; increase. We also observed a strong increase in D&lt;sub&gt;V&lt;/sub&gt; with decreasing fO&lt;sub&gt;2&lt;/sub&gt; for garnet-, clinopyroxene- and rutile-melt partitioning, while D&lt;sub&gt;Eu&lt;/sub&gt; shows the opposite trend. With increasing fO&lt;sub&gt;2&lt;/sub&gt; from FMQ-3 to FMQ+3, D&lt;sup&gt;Grt-Liq&lt;/sup&gt;&lt;sub&gt;Eu&lt;/sub&gt; increases by more than an order of magnitude and D&lt;sup&gt;Cpx-Liq&lt;/sup&gt;&lt;sub&gt;Eu&lt;/sub&gt; increases by a factor of 3. Our new data allow us to model the trace element composition of primary adakitic melts produced by melting of subducted oceanic crust at typical subarc depths of about 100 km. These melts are characterized by (i) a progressive enrichment in the most incompatible elements from about 0.1 (Sc) to 10 (Rb) times MORB values, (ii) strong Nb-Ta negative anomalies, (iii) Sr positive anomalies and (iv) a significant depletion in HREE and Y. Stronger Nb-Ta anomaly and lowers Ti, Hf and Zr contents are observed if more rutile is present in the source. Meanwhile, the contents of the most incompatible elements (Rb, Ba, U, Th), the positive Sr anomaly and Sr/Y and La/Yb ratios decrease with increasing degree of melting. We show that the calculated primary adakitic melts can evolve to form high-silica adakites following assimilation-fractional crystallization processes in the mantle wedge and crust. However, to preserve the positive Sr anomaly of high-silica adakites, plagioclase fractionation and sediment melting should remain moderate. Oxybarometry based on V/M ratios (M = Eu, Sc, Yb, Ti) indicates relatively reducing conditions (below FMQ-1) for the generation of parental melts of modern high-silica adakites and Archean high-pressure TTGs. Finally, the Sr/Y ratio of modern primitive arc lavas suggest that hybridization of primitive mantle wedge magmas with adakitic magmas is a significant process for relatively warm subd","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 336-353"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587132","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":"Carbonate-associated fluorescent dissolved organic matter (CAFDOM): Establishing a new proxy for dissolved organic matter in ancient oceans","authors":"Wei Wang ,&nbsp;Chao Li ,&nbsp;Matthew S. Dodd ,&nbsp;Hao Xu ,&nbsp;Meng Cheng ,&nbsp;Zihu Zhang ,&nbsp;Chunxia Yang ,&nbsp;Jun Hu ,&nbsp;Haiyang Wang ,&nbsp;Xinyang Chen ,&nbsp;Adrian Immenhauser","doi":"10.1016/j.gca.2026.03.006","DOIUrl":"10.1016/j.gca.2026.03.006","url":null,"abstract":"<div><div>Dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the modern ocean, playing a crucial role in the global carbon cycle and climate dynamics. However, there remains a lack of a proxy to directly track the composition and abundance of DOM in ancient oceans. In this study, we present a new approach for extracting and detecting carbonate-associated fluorescent dissolved organic matter (CAFDOM), aiming to establish it as a proxy for tracking DOM in ancient oceans. Our approach relies on three types of materials: (i) experimental samples with specifically defined properties, (ii) natural carbonate samples with known diagenetic histories (IODP core material, Marion Plateau), and (iii) well-preserved Ediacaran carbonate rocks from China. Following the protocol developed herein, the CAFDOM analysis of simulated carbonate samples shows good reproducibility for identifiable components, with relative standard deviations of less than 11% and average extraction rates exceeding 80%. Using fulvic acid as a natural model for DOM, carbonate precipitation experiments show that CAFDOM positively responds to solution DOM concentration in three distinct modes: (i) an exponential increase from zero with fulvic acid concentrations of 0–0.4 g/L; (ii) another exponential increase from zero with fulvic acid concentrations of 0.4–1.4 g/L; and (iii) a weak linear increase from a particular threshold with fulvic acid concentrations greater than 1.4 g/L. These modes are likely linked to critical shifts in the intermolecular forces of the DOM and its aggregation states during incorporation into the carbonate lattice. We propose that the abundance of DOM in ancient oceans can be constrained by combining the abundances with pairwise ratios of the CAFDOM components, and further evaluation and verification based on additional information of the investigated samples. Analysis of IODP core samples suggests that CAFDOM levels are likely influenced by the recrystallization from aragonite to calcite, authigenic carbonate formation, and replacement dolomitization. Based on the criteria established in this study, we analyzed Ediacaran carbonate samples (635–551 Myr) for CAFDOM. These data reveal significant variability in DOM in the Ediacaran marginal ocean, both in terms of concentration and fluorescent components. These findings are promising and suggest that, after conducting mineralogical characterization and screening for secondary alterations of sample material, CAFDOM can serve as an effective proxy for tracking DOM in ancient oceans.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 367-383"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147447943","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":"Basin-scale sulfur cycling driven by volcanism in Southern high latitudes during the Oceanic Anoxic Event 2","authors":"Zhiyu Zeng,&nbsp;Yilun Xu,&nbsp;Weiqi Yao","doi":"10.1016/j.gca.2026.03.023","DOIUrl":"10.1016/j.gca.2026.03.023","url":null,"abstract":"<div><div>The Oceanic Anoxic Event 2 (OAE2) represents the episode of large-scale ocean oxygen loss under extreme warmth in the late Cretaceous. The initiation of the OAE2 has been attributed to massive volcanic carbon emissions related to the emplacement of Large Igneous Provinces (LIPs), accompanied by significant perturbations in biogeochemical cycles of carbon, oxygen, and sulfur. Given the lower sulfate concentration in the Cretaceous ocean than it is today, its residence time was shorter under comparable fluxes, increasing the likelihood of spatial heterogeneity in the marine sulfur cycle. Since most existing data of seawater sulfate S-isotope ratio (δ³⁴S) for the OAE2 are reported from localities distant from LIPs, our understanding of the effects of volcanism on regional sulfur cycling and climate warming remains poorly constrained. In this study, we present marine barite δ³⁴S and TEX₈₆-derived sea-surface temperature (SST) records across the OAE2 from the Mentelle Basin, which was proximal to the active Kerguelen LIP (KLIP) in Southern high latitudes. Our result shows a basin-scale ∼5‰ decrease in seawater sulfate δ³⁴S during the OAE2, followed by a recovery to the higher-than-pre-excursion value in the post-OAE2. The simple box model attributes the δ³⁴S decline to a volcanic pulse of 6.96 × 10¹² mol isotopically light sulfur released into the ocean within 50 thousand years, which is approximately threefold of the background flux. The subsequent δ³⁴S overshoot requires a coeval increase in pyrite burial flux by 10%, indicating a modest expansion of anoxia in the Mentelle Basin. Meanwhile, the TEX₈₆-derived SST documents prolonged warmth persisting into the post-OAE2, providing an independent constraint on thermal forcing during the recovery phase. Sustained elevated SST in the high-latitude Southern Hemisphere would not only have promoted basin-scale deoxygenation and pyrite burial beyond the initial volcanic perturbation, but also reduced the meridional SST gradient and efficiency of poleward heat redistribution, thereby acting as positive feedback that helped sustain global warming. These findings reveal the response of basin-scale sulfur cycling and persistent warmth to volcanic activities in the high-latitude ocean across the OAE2.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 396-406"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465117","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":"Radiogenic 182W and 142Nd anomalies in a 2.7 Ga old basaltic lava flow indicate long-term preservation of early mantle heterogeneities","authors":"Jan L. Hellmann ,&nbsp;Igor S. Puchtel ,&nbsp;Vinciane Debaille ,&nbsp;Janne Blichert-Toft ,&nbsp;Richard J. Walker","doi":"10.1016/j.gca.2026.03.044","DOIUrl":"10.1016/j.gca.2026.03.044","url":null,"abstract":"<div><div>Understanding the origin and preservation of early mantle heterogeneities is essential for reconstructing Earth’s accretion and early differentiation history. This can be investigated using the short-lived ¹⁴⁶Sm–¹⁴²Nd and ¹⁸²Hf–¹⁸²W isotope systems, which provide insights into large-scale differentiation processes through ¹⁴²Nd and ¹⁸²W anomalies in Earth’s oldest rocks. In this study, we present ¹⁸²W data for Theo’s Flow, a thick, differentiated, mafic–ultramafic flow of tholeiitic affinity, as well as ¹⁴⁷Sm–¹⁴³Nd, ¹⁷⁶Lu–¹⁷⁶Hf, and ¹⁸⁷Re–¹⁸⁷Os isotope data and trace element concentrations, including highly siderophile elements, for Theo’s Flow and closely spatially and temporally associated Pyke Hill komatiites, both from the ∼2.7 Ga old Kidd-Munro Assemblage of the Abitibi greenstone belt, Ontario, Canada. Theo’s Flow samples are characterized by an average µ¹⁸²W value of +6.7±2.7, which, together with the previously reported positive µ¹⁴²Nd anomaly of +6.8±2.5, indicate long-term survival of mantle domains resulting from magmatic differentiation early in Earth’s history. If it is assumed that the bulk silicate Earth evolved with a suprachondritic Sm/Nd ratio, anomalies for both elements can be explained by a single silicate differentiation event at ∼4.54 Ga. Alternatively, if the bulk silicate Earth evolved with a chondritic Sm/Nd ratio, a model fractionation age of ∼4.45 Ga is obtained. In this case, due to extinction of ¹⁸²Hf by that time, the ¹⁸²W anomaly would have to have been generated by another process, such as derivation from a mantle source characterized by a deficit in late accreted materials. Regardless of the timing of the early silicate differentiation, the preservation of both ¹⁸²W and ¹⁴²Nd anomalies in the 2.7 Ga old rocks highlights the survival of early-formed mantle domains for nearly 1.8 Gyr after Earth’s formation. Comparison of isotopic and chemical data for Theo’s Flow with those for the Pyke Hill and Boston Creek komatiites, which were argued to have all been derived from melting in a single mantle plume, provides evidence for the survival of early mantle heterogeneities on a plume scale.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 320-335"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587147","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 isotopes as a new indicator for change in hydrology","authors":"Yadan Hu ,&nbsp;Fei Zhang ,&nbsp;Chen Chen ,&nbsp;Ying Xie ,&nbsp;Li Deng ,&nbsp;Xiangying Li ,&nbsp;Xiaolong Zhang ,&nbsp;Guang Bao ,&nbsp;Jinzhao Liu ,&nbsp;Zhangdong Jin","doi":"10.1016/j.gca.2026.03.018","DOIUrl":"10.1016/j.gca.2026.03.018","url":null,"abstract":"<div><div>Hydrology is a critical driving force that affects surface erosion and weathering, which regulates the long-term stability of Earth’s climate by removing atmospheric CO₂. However, reconstructing past hydroclimate remains a non-trivial challenge, due to the difficulty in isolating temperature effects. The negative correlation between globally compiled Li isotopes (δ⁷Li) and runoff suggests the potential of δ⁷Li as a hydrological proxy, yet confirming its validity still requires more field evidence. Here, we report the first weekly riverine δ⁷Li from a remote, rapidly eroding Muztag glacial basin (peak elevation of 7546 m) within the largest glacierized region of the mid-latitudes. Our results show remarkable seasonal changes in river δ⁷Li (up to ∼15‰), from 17.9‰ in the dry season to 2.5‰ in the wet season. The very low δ⁷Li in this tectonically active basin during the wet season contradicts the long-standing uplift-weathering hypothesis that intensified erosion increased incongruent continental weathering and higher riverine δ⁷Li. Instead, our findings unexpectedly exhibit a clear hydrological signal, with δ⁷Li showing a significant relationship with lake water levels but weak correlations with temperature. Changes in lake levels, together with riverine ⁸⁷Sr/⁸⁶Sr and Al/Si ratios, suggest that hydrologically driven variations in water–rock interaction time affect secondary mineral formation and seasonal riverine δ⁷Li. A further comparison of δ¹⁸O and δ⁷Li with temperature and lake level indicates that δ⁷Li provides a more suitable proxy for local hydrological changes than δ¹⁸O. Considering the debates regarding whether δ¹⁸O reflects changes in temperature or precipitation at regional or global scales, our findings have important implications for using δ⁷Li in lacustrine sedimentary records (e.g., authigenic carbonates) as a promising tool to decode past hydrologic state, thereby helping to isolate temperature effect.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 384-395"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147447933","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":"Climate signals in coral lipids: Temperature-driven variations in lipid distribution and δ13C of fatty acids","authors":"Yi Song ,&nbsp;Jianrong Huang ,&nbsp;Kefu Yu ,&nbsp;Thomas J. Algeo ,&nbsp;Xianyu Huang ,&nbsp;Huan Yang ,&nbsp;Jiabao Wang ,&nbsp;Mingsi Zang ,&nbsp;Yingzhao Wang","doi":"10.1016/j.gca.2026.03.036","DOIUrl":"10.1016/j.gca.2026.03.036","url":null,"abstract":"<div><div>Corals represent high-resolution modern and geological archives for reconstructing marine environmental shifts. Although the content and distribution of lipids in modern corals are known to be temperature-sensitive, the quantitative relationships between temperature and various lipid compounds have not been systematically investigated to date. Here, we focus on the development and calibration of emerging lipid-based proxies by systematically investigating the temperature sensitivity of the distributions and concentrations of fatty acids (FAs) and sterols in scleractinian corals (<em>Porites lutea</em> and <em>Acropora millepora</em>) from the western coast of Weizhou Island. Corals were grown in controlled aquarium experiments over a temperature range of 16–32 °C for 2 to 13 weeks, yielding lipid distributions and compound-specific carbon isotopic compositions (δ¹³C) of fatty acids that were evaluated in the context of global coral lipid research. Our results reveal that lipids in soft tissue (i.e., the coral host and algal symbionts), exoskeleton (green layer), and endoskeleton (white layer) exhibit differential responses to temperature change, providing a multi-proxy framework for environmental reconstruction. The relative contents of (C_16:1 + C_18:1)/(C_16:0 + C_18:0) show a linear relationship to temperature within the 11–32 °C range, with threshold effects observed for C_16:0, C_18:0 and C_16:1 at ∼26 °C, making these proxies effective at discriminating between cold-water and tropical conditions. Compound-specific carbon isotopic results show positive correlations between temperature and δ¹³C_16:0FA and δ¹³C_18:0FA in soft tissue and exoskeleton, validating their potential as an indicator of coral response to temperature changes over a range of water depths. Additionally, algal-derived sterols show stepwise or linear relationships with temperature variation, reflecting the differential responses of coral-hosted algae to climate change. By providing quantitative calibrations, this study refines the use of coral lipid archives for interpreting deep-time paleoclimate records as well as for assessing the risk posed to coral reef ecosystems by global warming.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"423 ","pages":"Pages 446-460"},"PeriodicalIF":5.0,"publicationDate":"2026-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147495453","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}