Geochimica et Cosmochimica Acta最新文献

{"title":"Compound-specific carbon and hydrogen isotope analysis traces archaeal lipid signatures in cold seep marine systems","authors":"Katherine Keller ,&nbsp;Sebastian Kopf ,&nbsp;Jamie McFarlin ,&nbsp;Ashley Maloney ,&nbsp;Jeemin H. Rhim ,&nbsp;Felix J. Elling ,&nbsp;Kemi Ashing-Giwa ,&nbsp;Isabel Baker ,&nbsp;Amanda Calhoun ,&nbsp;Ann Pearson","doi":"10.1016/j.gca.2025.08.017","DOIUrl":"10.1016/j.gca.2025.08.017","url":null,"abstract":"<div><div>Compound-specific stable isotope analyses of archaeal lipid biomarkers can provide useful information on biogeochemical cycling in marine systems. While most work has focused on carbon isotopes, the analysis of hydrogen isotope ratios (δ²H) remains underexplored for its potential to characterize sources of lipids and metabolic diversity in marine sedimentary systems. This study examines the δ²H values of archaeal biphytanes, derivatives of the parent isoprenoid glycerol dialkyl glycerol tetraether lipids (iGDGTs), as a tool to discriminate archaeal sources to sediments collected from Astoria Canyon, a cold-seep system along the Cascadia Margin. Using a mixing model applied to biphytane δ²H values obtained from individual iGDGTs, we estimate the δ²H signatures of the two primary endmember sources in this location: planktonic and benthic methane cycling communities. Additionally, we determine the structural biphytane combinations within each parent iGDGT. Our findings indicate that planktonic and benthic methane-cycling archaea both generate highly fractionated lipids, with modeled δ²H signatures of –308 ‰ and –222 ‰, respectively. When combined with reported compound-specific δ¹³C values for the corresponding iGDGTs, the dual-isotope approach allows us to determine the mean δ²H signatures of the two dominant archaeal communities, providing new endmember constraints for lipid source apportionment as well as the underlying biphytane structures comprising intact iGDGTs. These findings provide an interpretative framework for applying compound-specific stable isotopic approaches to disentangle sediment iGDGT sources and track methane cycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 309-321"},"PeriodicalIF":5.0,"publicationDate":"2025-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900629","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":"Clumped isotope reordering kinetics in rudist fossils: Impact of burial history and paleoclimatic implications","authors":"Barbora Křížová ,&nbsp;Niels J. de Winter ,&nbsp;Martin Ziegler ,&nbsp;Alberto Riva ,&nbsp;Philippe Claeys ,&nbsp;Steven Goderis ,&nbsp;Deborah Arbulla ,&nbsp;Gianluca Frijia","doi":"10.1016/j.gca.2025.08.013","DOIUrl":"10.1016/j.gca.2025.08.013","url":null,"abstract":"<div><div>The low-Mg calcite shells of bivalves can record paleotemperatures over geological time scales. Stable oxygen isotope thermometry (δ¹⁸O) is a widely used paleotemperature proxy for past oceans. However, it relies on an estimate of the δ¹⁸O of the calcification fluid. Carbonate clumped isotope analysis, a paleothermometer independent of the δ¹⁸O of water, overcomes this issue and is a valuable tool for reconstructing Phanerozoic paleotemperatures. In both oxygen and clumped isotope paleothermometry, preservation of the original isotopic signal is essential for paleoenvironmental reconstructions. Apart from recrystallization, clumped isotope resetting at elevated burial temperatures can affect the clumped isotope composition. In this study, we analyzed Late Cenomanian to Santonian rudist bivalves from two regions with different time–temperature evolution (Friuli-Venezia Giulia, in Italy and southern Istria, in Croatia). The reconstructed Δ₄₇-based temperatures (T(Δ₄₇)) differ significantly between the two regions, ranging from 34 to 41 °C in the Istria region and 73 to 101 °C in the Friuli-Venezia Giulia region. Thorough screening excluded any significant contribution of diagenetic alteration of the chemical composition and shell texture, pointing towards clumped isotope resetting in the rudist fossils from Friuli-Venezia Giulia.</div><div>Modeling solid-state reordering effects in the Friuli-Venezia Giulia rudists suggests that the rudist T(Δ₄₇) should be interpreted cautiously and demonstrates the need for research on fossil-specific reordering kinetics. The available data do not permit a definite conclusion on rudist reordering kinetics. However, the rudist data correspond most closely to the reordering kinetics similar to that of the belemnites, resulting in resetting at low burial temperatures and at a faster rate. These results further demonstrate the variability in clumped isotope reordering kinetics in calcite fossils.</div><div>Excluding the effect of clumped isotope resetting on the Istrian rudists allowed for δ¹⁸O_seawater reconstruction. The resulting values of −0.1 to 1.4 ‰ are within the range observed in modern oceans but are high compared with the assumed Late Cretaceous value of −1 ‰. These results point out the importance of using δ¹⁸O_seawater-independent paleothermometers, especially in the shallow marine environment.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 282-294"},"PeriodicalIF":5.0,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900631","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":"An experimental investigation of the redox reactions between carbonates and pyrrhotite at high P-T conditions: insights into diamond formation in deep subduction zones","authors":"Jintao Zhu ,&nbsp;Renbiao Tao ,&nbsp;Wenqing Sun ,&nbsp;Takayuki Ishii ,&nbsp;Yunxiu Li ,&nbsp;Huijuan Li ,&nbsp;Vincenzo Stagno ,&nbsp;Lifei Zhang","doi":"10.1016/j.gca.2025.08.012","DOIUrl":"10.1016/j.gca.2025.08.012","url":null,"abstract":"<div><div>Subducted carbonates can be reduced into graphite/diamond through redox reactions involving metallic alloys (e.g., Fe⁰) or silicate minerals (e.g., Fe²⁺-bearing minerals) in the deep mantle. Pyrrhotite (FeS), an essential carrier of reduced sulfur (S²⁻), is commonly found as inclusions in natural diamond, mantle-derived xenoliths, and subducted slabs alongside various carbonates. Although carbonate/diamond and pyrrhotite show strong associations, the interplay of carbon and sulfur and the sulfide-induced formation mechanism of diamonds in deep subduction zones remain poorly constrained. In this study, we conducted a series of experiments to investigate possible redox reactions between aragonite/magnesite (CaCO₃/MgCO₃) and pyrrhotite (FeS) with or without SiO₂ and Al₂O₃ added to the bulk compositions under pressure and temperature conditions of 4–10 GPa and 800–1600 °C. Based on high-pressure experimental results combined with thermodynamic modelling, we found that the transformation of pyrrhotite to pyrite (FeS₂) under high-pressure and low-temperature conditions can simultaneously reduce carbonates to graphitic carbon (C). High contents of SiO₂ and Al₂O₃ in the bulk compositions could promote the formation of pyrite + graphite + Fe²⁺-rich silicates (e.g., hedenbergite and almandine). Therefore, we propose that the subduction of oceanic slabs, including sialic sediments and carbonated eclogites (e.g., those enriched in carbonate, quartz, feldspar, and mica minerals), along a relatively cold geotherm into the deep mantle can drive efficient redox reactions between carbonates and sulfides, potentially contributing to the formation of diamonds in the deep mantle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 265-281"},"PeriodicalIF":5.0,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900632","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":"Enhanced microbial degradation of methylmercury by montmorillonite","authors":"Qin Liu ,&nbsp;Hui Yin ,&nbsp;Baohua Gu ,&nbsp;Xin-Quan Zhou ,&nbsp;Xiaolong Yue ,&nbsp;Qiaoyun Huang ,&nbsp;Yu-Rong Liu","doi":"10.1016/j.gca.2025.08.014","DOIUrl":"10.1016/j.gca.2025.08.014","url":null,"abstract":"<div><div>The potent neurotoxic methylmercury (MeHg) can be detoxified through microbial demethylation. The colonization and functions of microbes are influenced by minerals in the environment; however, the role of minerals in mediating microbial degradation of MeHg remains poorly understood. Here, we investigated the effects of three typical soil minerals (i.e., montmorillonite, ferrihydrite, and birnessite) on MeHg degradation by <em>Chitinophaga dinghuensis</em>. The addition of montmorillonite increased the MeHg degradation efficiency by <em>C</em>. <em>dinghuensis</em> from 27.27 % to 44.84 % in 120 h, representing a 1.6-fold improvement compared to the mineral-free system, whereas ferrihydrite or birnessite had negligible effects on the MeHg degradation. This could be attributed that montmorillonite offered bacterial colonization surfaces for survival and alleviated MeHg-induced cell toxicity by reducing the production of intracellular reactive oxygen species. Additionally, montmorillonite released magnesium ions to improve cell metabolisms for the mineral-enhanced demethylation of MeHg. We also found that Fe²⁺ oxidation at the bacteria-montmorillonite interface could further contribute to the enhanced MeHg degradation by bacteria. Together, our work provides new insights into the crucial role of montmorillonite in mediating microbially-driven MeHg degradation, with important implications for understanding Hg biogeochemical cycles and mitigating environmental risks of the neurotoxin.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"405 ","pages":"Pages 44-54"},"PeriodicalIF":5.0,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144867004","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":"Zinc isotopic evidence for enhanced oceanic primary productivity during termination of the late Ediacaran Shuram Excursion","authors":"Jinzuo Tong ,&nbsp;Meng Cheng ,&nbsp;Jun Hu ,&nbsp;Xinyang Chen ,&nbsp;Haiyang Wang ,&nbsp;Thomas J. Algeo ,&nbsp;Mingcai Hou ,&nbsp;Chao Li","doi":"10.1016/j.gca.2025.08.015","DOIUrl":"10.1016/j.gca.2025.08.015","url":null,"abstract":"<div><div>The recovery from the largest negative carbon isotope excursion in Earth history, the late Ediacaran Shuram Excursion, is thought to have been related to enhanced primary productivity, but direct evidence supporting this hypothesis is lacking. Zinc isotopes in marine sediments are a promising proxy to constrain oceanic productivity as well as organic matter burial rates. To explore secular variation in oceanic productivity and its role in recovery from the Shuram Excursion, Zn isotopes, major- and trace-element, and iron speciation data were generated for black shales from Member IV of the Ediacaran Doushantuo Formation in two South China sections (Jiulongwan and ZK6305). Redox proxy data reveal predominantly euxinic bottom waters, and salinity proxy data indicate mostly high-brackish conditions (∼15–30 psu) linked to moderate basinal watermass restriction. These conditions preserved a record of contemporaneous seawater Zn isotopic compositions, revealing a positive δ⁶⁶Zn excursion in the upper part of the study sections (from +0.31 ± 0.02 ‰ to +0.70 ± 0.01 ‰ at Jiulongwan, and from +0.35 ± 0.03 ‰ to +0.62 ± 0.04 ‰ at ZK6305, 2SD) that record elevated oceanic productivity and enhanced organic matter burial. This development may have led to re-coupling of the carbonate and organic carbon isotope records by elevating the relative proportion of particulate organic carbon relative to dissolved organic carbon in the sediment. Enhanced burial of organic carbon may have also removed isotopically light carbon from the ocean, thus promoting recovery from peak low values in marine carbon isotope records. Our study highlights the critical role of oceanic productivity in attenuating perturbations of the marine carbon cycle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"405 ","pages":"Pages 66-79"},"PeriodicalIF":5.0,"publicationDate":"2025-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144867007","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":"Zircon solubility modulated by boron in hydrous granitic melts","authors":"Jinhua Huang ,&nbsp;Renzhi Zhu ,&nbsp;Huaiwei Ni","doi":"10.1016/j.gca.2025.08.008","DOIUrl":"10.1016/j.gca.2025.08.008","url":null,"abstract":"<div><div>Granitic rocks associated with zircon deposits often contain notable boron (B), suggesting a potentially crucial role of B in zircon mineralization. However, the influence of B on the solubility of zircon in granitic magma remains unclear. In this study, the solubility of zircon in three granitic melts (peralkaline, metaluminous, and peraluminous) with approximately 6 wt% H₂O (i.e., water-saturated) and up to 7.7 wt% B₂O₃ was investigated at 800 °C and 2 kbar using a cold-seal vessel. As melt B₂O₃ content increased from 0 to 1 wt%, ZrO₂ content always increased, from 2.10 to 2.60 wt% in the peralkaline melt (ASI = 0.63), from 0.20 to 0.26 wt% in the metaluminous melt (ASI = 0.98), and from 0.02 to 0.03 wt% in the peraluminous melt (ASI = 1.20). However, with a further increase of B₂O₃ to 7.7 wt%, the ZrO₂ content in all of the three granitic melts steadily decreased to approximately one-sixth of the maximum value. Raman and nuclear magnetic resonance spectroscopic measurements suggest that the shift in zircon solubility behavior is related to structural change involving boron and oxygen. The turning point at 1 wt% B₂O₃ marks a transition from predominantly trigonally coordinated boron in low-boron melts, producing non-bridging oxygen favorable to zirconium (Zr) incorporation, to the prevalence of tetrahedrally coordinated boron in high-boron melts promoting bridging oxygen. The experimental results imply that the mechanism and behavior of zircon saturation can be different for different boron-bearing magmas. In granitic magma (usually with &lt;1 wt% B₂O₃), B serves to promote the Zr-carrying capacity of magma, which is in favor of Zr mineralization. By contrast, in pegmatitic magma (mostly with &gt;1 wt% B₂O₃), the Zr-carrying capacity of magma is low, and B is harmful to Zr mineralization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"405 ","pages":"Pages 15-24"},"PeriodicalIF":5.0,"publicationDate":"2025-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144826750","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":"Corrigendum to “Multiple fluid-rock interactions in the subduction channel evidenced by magnesium isotope”. [Geochim. et Cosmochim. Acta 403 (2025) 67–78]","authors":"Yongxiang Yao, Yuanyuan Xiao, Weidong Sun","doi":"10.1016/j.gca.2025.08.001","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.001","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900679","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":"Distinct pathways of Mg isotope fractionation during biotite weathering in granitoid weathering profiles","authors":"Jong-Sik Ryu, Gi Young Jeong, Albert Chang-sik Cheong, Fang-Zhen Teng","doi":"10.1016/j.gca.2025.08.005","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.005","url":null,"abstract":"Magnesium (Mg) isotopes have emerged as powerful tracer of chemical weathering processes, providing insights into the mobilization of Mg from minerals and its role in regulating seawater chemistry, global biogeochemical cycle, and long-term climate change. However, the relationship between mineral weathering and Mg isotope fractionation remains poorly constrained in natural weathering systems, particularly with respect to the direction and magnitude of isotope fractionation. Here, elemental and Mg isotope geochemistry in two types of biotite collected from in–situ granitoid weathering profiles were investigated, along with their mineralogical properties. While positive correlations between depth and elemental concentrations occur in both types of biotite, Mg isotopic variations are different: 1) oxidized biotites are enriched in <ce:sup loc=\"post\">26</ce:sup>Mg, up to +0.4 ‰ in δ<ce:sup loc=\"post\">26</ce:sup>Mg, via diffusive release of octahedral <ce:sup loc=\"post\">24</ce:sup>Mg during iron oxidation; 2) hydrobiotites (1:1 regularly interstratified biotite-vermiculite) have the same δ<ce:sup loc=\"post\">26</ce:sup>Mg as fresh biotite at all depths, indicating that newly formed vermiculite inherits the δ<ce:sup loc=\"post\">26</ce:sup>Mg of biotite. Furthermore, δ<ce:sup loc=\"post\">26</ce:sup>Mg values in both types of biotite display little correlation with the abundance of secondary phases, indicating negligible effects of secondary phases (i.e. vermiculite and kaolinite) on Mg isotope fractionation. This study provides the first evidence that, at the incipient stage of biotite weathering, oxidized biotite releases isotopically light Mg, with a fractionation factor of up to 1.0024 ± 0.0012 (2σ), whereas hydrobiotite retains the δ<ce:sup loc=\"post\">26</ce:sup>Mg signature of fresh biotite regardless of weathering intensity. These findings highlight that diffusive Mg isotope fractionation during iron oxidation in natural weathering systems over geological timescales may dominate over other processes at the onset of silicate weathering.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900680","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":"Petrological and thermodynamic constraints on carbonate stability in altered oceanic crust subducted to subarc depths: Insights from carbonate-bearing eclogites in the Western Alps","authors":"Zeng-Li Guo ,&nbsp;Jin-Xue Du ,&nbsp;Li-Fei Zhang ,&nbsp;Thomas Bader ,&nbsp;Ren-Biao Tao ,&nbsp;Ze-Ming Zhang ,&nbsp;Kurt Bucher ,&nbsp;Ting-Nan Gong ,&nbsp;Jin-Hong Yu","doi":"10.1016/j.gca.2025.08.010","DOIUrl":"10.1016/j.gca.2025.08.010","url":null,"abstract":"<div><div>Altered carbonates within the oceanic crust, which constitute a major carbon reservoir in subducting slabs, remain poorly constrained with respect to the factors controlling their deep recycling processes. In this study, we investigate carbonate-bearing eclogites from the Zermatt–Saas ophiolite by integrating petrological analysis, fluid inclusion studies and multi-scenario thermodynamic modelling to constrain decarbonation processes in subducted altered oceanic crust. Both studied magnesite- and dolomite-bearing eclogites experienced high-pressure metamorphism under low subduction zone thermal gradients (&lt; 240 °C/GPa). The magnesite-bearing sample records peak conditions of ∼2.80 GPa at 575 °C and higher oxygen fugacity (ΔFMQ = +1.3 ± 0.86) during subduction and exhumation, in contrast to the dolomite-bearing sample (∼2.45 GPa at 575 °C; ΔFMQ = +0.4 ± 0.3). Decarbonation modelling indicates carbon losses of approximately 30 % and 43 %, respectively, driven by carbonate dissolution and fluid-induced metamorphic decarbonation during subduction and exhumation. CO₂-bearing fluid inclusions in host magnesite were primarily trapped during recrystallization linked to carbonate phase transitions under high-pressure conditions. The survival of subducted carbon is governed by multiple factors, including the carbon phase (graphite vs. carbonate), bulk-rock carbonate content, subduction zone thermal gradient and external fluid infiltration. Quantitative modelling of carbon survival across a range of subduction zone thermal gradients indicates that in cold subduction zones (&lt; 320 °C/GPa), decarbonation is primarily controlled by the dehydration depths of lawsonite and epidote. In contrast, in warmer subduction zones, decarbonation is predominantly driven by metamorphic reactions, either occurring under dehydration-suppressed conditions or associated with epidote–hornblende breakdown. Open-system modelling reveals that complete decarbonation at lower temperatures (e.g., ∼500 °C) requires extensive fluid infiltration, whereas at subarc depths with higher P–T conditions, even minimal infiltration can significantly enhance decarbonation efficiency. Lawsonite dehydration appears to dominate the decarbonation process during subduction along thermal gradients below 270 °C/GPa, resulting in enhanced carbon release in colder subduction zones before reaching subarc depths. In contrast, thermal gradients exceeding ∼330–360 °C/GPa lead to nearly complete decarbonation prior to subarc depths. These results provide theoretical constraints on the initiation and episodic nature of deep carbonate cycling during the secular thermal evolution of subduction zones. Our findings elucidate the pivotal role of subducted carbonates, hosted within altered oceanic crust, in mediating deep mantle oxidation over Earth’s geological history.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"405 ","pages":"Pages 205-228"},"PeriodicalIF":5.0,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900682","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 impact of CO2-charged fluids on the aqueous geochemistry of terrestrial aquifers","authors":"G.S. Lollar ,&nbsp;M.R. Osburn ,&nbsp;C.P. Casar ,&nbsp;E. Rutledge ,&nbsp;O. Warr","doi":"10.1016/j.gca.2025.08.009","DOIUrl":"10.1016/j.gca.2025.08.009","url":null,"abstract":"<div><div>Understanding the formation and evolution of subsurface CO₂-rich terrestrial fluids and reservoirs is key for modelling the storage of CO₂ in the crust, fracture-controlled fluid flow, and/or diffusive transport of fluids from deep crustal settings. However, migration and exchange mechanisms associated with CO₂-rich environments remain poorly constrained. In at least one natural CO₂-rich setting, a Precambrian crystalline brine component has been postulated based on δ¹⁸O and δ²H signatures which plot above the Global Meteoric Water Line. In this study we evaluate the intriguing potential role of migration and mixing of deep fluids in the shallow subsurface using a novel geochemical and microbiological framework approach which incorporates noble gas, stable isotope, and microbial diversity-based approaches. Through targeting a series of 10 springs which sample depths of up to 250 m at Saratoga Springs, NY, USA, this integrated approach finds no evidence of a deep shield brine component and reveals only migration of a principally deep crustally-derived CO₂ (87.2–99.3 %) with a minor mantle component. Instead, this study reveals how putative CO₂ dissolution-enhanced water–rock interaction coupled with ≤17 % CO₂-H₂O ¹⁸O isotopic exchange can produce the observed aqueous geochemical composition, including the apparent shield brine signal. Microbial community data presented here also suggest distinct assemblages between shallow, freshwater and deep, saline spring fluids in line with geochemical interpretations. Crucially, our novel integrated approach highlights how migrating CO₂-rich phases in subsurface environments can overprint and drive geochemical reactions in the subsurface to produce aqueous geochemistries which mimic characteristics of unrelated deep fluid systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"405 ","pages":"Pages 188-204"},"PeriodicalIF":5.0,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144901763","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}