Geochimica et Cosmochimica Acta最新文献

{"title":"Revisiting zircon-melt REE partitioning systematics: new insight into shallow crustal melting on early Earth","authors":"Sheng Shang,&nbsp;Haoxiong He,&nbsp;Wim van Westrenen,&nbsp;Fraukje M. Brouwer,&nbsp;Yanhao Lin","doi":"10.1016/j.gca.2026.04.039","DOIUrl":"10.1016/j.gca.2026.04.039","url":null,"abstract":"<div><div>Trace element abundances in ancient magmatic zircon could provide unique insights into Hadean and early Archaean felsic magmatism, yet the rare earth element (REE) partition coefficients (D_REE) between zircon and melt needed to translate zircon abundances to melt abundances remain poorly constrained. We combined results of eight new high-temperature partitioning experiments (1000–1400 °C) with prior data to quantify D_REE systematics and show their strong dependence on both temperature and melt composition. An empirical lattice strain partitioning model for trivalent REEs was established, enabling re-assessment of reconstructed parental melt compositions from the REE abundances in ancient zircons. The inferred chondrite-normalized (La/Yb)_N ratios in zircons from the Hadean and early Archaean are lower than those of later Archaean TTGs and adakites. This suggests a transition from garnet-absent, shallow crustal melting in the earliest Earth to later Archaean magmatism dominated by the involvement of deeper garnet signatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 171-186"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148541749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dating and tracing highly fractionated granitic systems: resolving isotopic disturbance and metal source in the 2.7 Ga Tanco pegmatite","authors":"Zelong Shi,&nbsp;Ye Zheng,&nbsp;Jieqi Xing,&nbsp;Bernd Lehmann,&nbsp;Yang Li","doi":"10.1016/j.gca.2026.06.011","DOIUrl":"10.1016/j.gca.2026.06.011","url":null,"abstract":"<div><div>Rare-metal pegmatites are primary repositories of Li, Cs, Ta, and Sn, yet their genesis remains debated, largely due to difficulties in constraining the timing, source, and evolution of highly evolved granitic systems. These challenges are particularly pronounced in Archean terranes, where radiation damage and later thermal events promote isotopic disturbance. The Tanco pegmatite in Canada, a classic Li–Cs–Ta (LCT) system, provides an ideal case to address these issues. Previous U–Pb and Rb–Sr datasets have been used to indicate pegmatite formation at ∼2.64 Ga from S-type melts, followed by prolonged subsolidus fluid activity lasting for tens of millions of years. New in situ U–Pb analyses of cassiterite and columbite–tantalite (n = 28) define a lead-loss array with an upper-intercept age of 2.70 ± 0.03 Ga, representing primary crystallization of the Tanco pegmatite. This age overlaps with that of the nearby Birse Lake pluton, suggesting that pegmatite emplacement was contemporaneous with regional magmatism and potentially genetically related to the pluton. Muscovite from the Tanco pegmatite is exceptionally enriched in Rb (&gt;10⁴ ppm) with high ⁸⁷Rb/⁸⁶Sr ratios (10⁴–10⁶), resulting in negligible common Sr and enabling single-mineral Rb–Sr dating. The wide spread in muscovite apparent Rb–Sr ages (1.9–2.8 Ga, n = 374) necessitates redistribution of radiogenic ⁸⁷Sr long after pegmatite crystallization. Because little radiogenic ⁸⁷Sr would have accumulated during pegmatite cooling, subsolidus hydrothermal activity at that stage cannot explain the observed age dispersion. Instead, the scattered ages likely record diffusion-driven radiogenic ⁸⁷Sr redistribution during a later thermal overprint, consistent with the cassiterite/columbite-tantalite U–Pb lower-intercept age of 0.3 ± 0.1 Ga. Importantly, anomalously high (⁸⁷Sr/⁸⁶Sr)_initial values do not indicate an S-type source, but instead reflect radiogenic Sr redistribution. Cassiterite δ¹⁸O values of 4.7 ± 0.8 ‰ (2SD; n = 28) correspond to equilibrium zircon δ¹⁸O values of ∼7.5 ± 0.8 ‰ at 600 ± 50 °C, indicating derivation from a hybrid melt containing &lt;30% S-type component, rather than a purely S-type source. The extreme enrichment of incompatible elements in the Tanco pegmatite reflects advanced fractional crystallization, which progressively concentrates rare metals in the residual melt. Our results reconcile inconsistencies in existing datasets, suggest a genetic link between the Tanco pegmatite and the Birse Lake pluton, and demonstrate that isotope systems in highly evolved granitic rocks are readily modified by diffusion and thermal/hydrothermal overprinting, requiring integrated multi-isotopic approaches to constrain their genesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 68-81"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148289477","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":"Stagnant groundwater in a large subterranean estuary revealed by 226Ra/230Th disequilibria","authors":"Liuting Yuan,&nbsp;Chong Sheng,&nbsp;Yilin Cheng,&nbsp;Qingquan Hong,&nbsp;Yaojin Chen,&nbsp;Shouye Yang,&nbsp;Yiming Luo,&nbsp;Roger Francois,&nbsp;Pinghe Cai","doi":"10.1016/j.gca.2026.04.037","DOIUrl":"10.1016/j.gca.2026.04.037","url":null,"abstract":"<div><div>During the past decades, large enrichments of ²²⁶Ra in coastal waters have been reported worldwide and were used to infer large submarine groundwater discharge into the sea. However, this recognition has not been widely appreciated outside the hydrology community because the exact location of discharge and its driving mechanisms remain largely unknown to date. Here, we report the first measurements of ²²⁶Ra/²³⁰Th disequilibria in sediment cores drilled from a large subterranean estuary in the Pearl River delta, China. In stark contrast to the surface Pearl River estuary, no significant deficit of ²²⁶Ra relative to ²³⁰Th was observed in aquifer sediments of the subterranean estuary except for the upper ∼5 m, which corresponds roughly to the length scale of ²²⁶Ra diffusion into the water column. Based on a transport-reaction model of ²²⁶Ra, we show that the subterranean estuary is stagnant and the replenishing rate of the groundwater must be &lt;0.01 yr⁻¹. Furthermore, we show that ²²⁶Ra, dissolved inorganic carbon, and nutrients are mainly released from surface sediments of several meters, likely via local transport processes occurring at the sediment–water interface. We advocate that future studies aiming to resolve sources of the large ²²⁶Ra enrichments in coastal waters should focus on the regeneration of ²²⁶Ra in surface sediments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 160-170"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148541748","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 cerium isotope fractionation during basalt-rhyolite magmatic differentiation","authors":"Peng Wu,&nbsp;Fang Liu,&nbsp;Lei Li,&nbsp;Zhengjie Zhao,&nbsp;Jiaojiao Wu,&nbsp;Wenke Wang,&nbsp;Yajun An,&nbsp;Xin Li,&nbsp;Paul Savage,&nbsp;Mingxing Ling,&nbsp;Zhaofeng Zhang","doi":"10.1016/j.gca.2026.02.032","DOIUrl":"10.1016/j.gca.2026.02.032","url":null,"abstract":"<div><div>Cerium (Ce) is an incompatible and redox-sensitive element, and stable Ce isotopes are emerging geochemical proxies for tracing Earth’s surface redox evolution that is complementary to traditional elemental ratios (e.g., Ce/Ce*). However, the robust application of this proxy requires a fundamental understanding of its behavior during high-temperature processes, which remains poorly constrained. To address this issue, we present Ce isotope compositions for a well-characterized suite of volcanic rocks from Hekla, Iceland, which spans a compositional range from basalt to rhyolite that were considered to have formed via fractional crystallization and/or mixing of cogenetic melts. Twenty-three samples yield a relatively uniform δ¹⁴²Ce ranging from −0.007‰ to 0.070‰, with an average of 0.032 ± 0.045‰ (2 S.D.). The average δ¹⁴²Ce of each lithology is 0.031 ± 0.032‰ for basalt, 0.019 ± 0.035‰ for basaltic andesite, 0.040 ± 0.045‰ for andesite, 0.064 ± 0.011‰ for dacite, and 0.009 ± 0.027‰ for rhyolite, respectively. Although a subtle δ¹⁴²Ce variations in the evolved rocks is observed, the total Ce isotope fractionation (Δ¹⁴²Ce = ∼0.07‰) is barely beyond the current analytical uncertainty, implying that the Ce isotope fractionation during magmatic differentiation at Hekla is limited. This is supported by the strongly incompatible behavior of Ce and near-constant oxygen fugacity throughout the Hekla differentiation sequence, indicating that the crystallizing phases remove only negligible amounts of Ce from the melt and therefore that significant fractionation of Ce isotopes is unlikely. Furthermore, mantle melting degree or melting depth have no effect on the Ce isotopes. Our findings demonstrate that high-temperature igneous processes are unlikely to significantly overprint primary Ce isotope signatures. Consequently, Ce isotopes may provide a robust tracer for investigating deep sediment recycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 241-250"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147279492","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":"Oceanic chlorine enrichment preceding end-Permian warming linked to volcanic degassing","authors":"Jing-Yi Wang,&nbsp;Yang Li,&nbsp;Hai-Jun Song,&nbsp;Ruo-Yu Bai,&nbsp;Xian-Hua Li","doi":"10.1016/j.gca.2026.04.008","DOIUrl":"10.1016/j.gca.2026.04.008","url":null,"abstract":"<div><div>Chlorine contents in bioapatite represent an emerging but largely untested geochemical proxy for reconstructing oceanic chlorinity variations in deep time. The Permian–Triassic mass extinction (PTME) represents the most severe biotic crisis in Earth’s history and is temporally associated with magmatism of the Siberian Traps Large Igneous Province (STLIP) and coeval felsic volcanism in South China. Although rapid warming, marine anoxia, and ocean acidification driven by volcanic degassing and sedimentary contact metamorphism have been widely invoked as primary kill mechanisms, the sequence and nature of environmental perturbations preceding the extinction remain incompletely resolved. Here we present in situ analyses of conodont δ¹⁸O and chlorine (Cl) contents from the Jianzishan section, South China, to constrain short-term environmental changes across the Permian–Triassic transition. Sea-surface temperatures (SSTs) derived from conodont δ¹⁸O rise from ∼18.5 to ∼27.5 °C, with peak warming lagging the extinction onset by &gt;0.04 Myr. In contrast, Cl contents from the same conodont exhibit an abrupt increase from ∼0.2 to &gt;0.5 wt% followed by a rapid return to background levels prior to the onset of the end-Permian extinction. From a mass balance perspective, such a Cl anomaly is unlikley to have occurred on a global scale. We therefore interpret this transient Cl spike as recording a short-lived increase in marine chlorine availability at the study section, although a decrease in oceanic F cannot be excluded. We consider halogen-rich volatile release during the sill-emplacement stage of STLIP magmatism and/or coeval felsic volcanism in South China is the most likely mechanism for this Cl anomaly. Our results suggest that short-lived halogen-rich volatile release may represent an early environmental perturbation preceding the end-Permian mass extinction, with subsequent warming amplifying stress on already vulnerable ecosystems. More broadly, this study demonstrates that in situ Cl analysis of conodont apatite can resolve short-lived oceanic chemical perturbations at high stratigraphic resolution, establishing bioapatite Cl as a promising proxy for paleo-ocean halogen cycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 266-274"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681380","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":"Photosynthesis-induced carbonate precipitation amplifies calcium isotope differences between surface water and groundwater in carbonate-rich watersheds","authors":"Mingyu Shao,&nbsp;Zaihua Liu,&nbsp;Sibo Zeng,&nbsp;Ding He,&nbsp;Zhaofeng Zhang,&nbsp;Hao Yan,&nbsp;Qian Bao,&nbsp;Liguo Tang,&nbsp;Xin Li,&nbsp;Hailong Sun,&nbsp;Junyao Yan,&nbsp;Liangxing Shi","doi":"10.1016/j.gca.2026.04.028","DOIUrl":"10.1016/j.gca.2026.04.028","url":null,"abstract":"<div><div>Carbonate-rich surface waters provide a natural laboratory for evaluating how photosynthesis modulates calcium (Ca) isotopes (<em>δ</em>^44/40Ca) through photosynthesis-induced CaCO₃ precipitation. Here, we conducted a comparative study at the Shawan Karst Water–Carbon Cycle Test Site (Southwest China) using five artificial groundwater-surface-water systems with identical hydrogeologic boundaries but contrasting land-use types. These systems were designed to generate gradients in groundwater Ca²⁺/Dissolved Inorganic Carbon (DIC) supply and aquatic primary productivity. We integrated hydrochemistry, elemental analyses, stable isotope measurements (δ²H, δ¹⁸O, δ¹³C_DIC, and <em>δ</em>^44/40Ca), mineralogical evidence, dissolved organic matter characterization, and isotope fractionation modeling to identify the key controls on <em>δ</em>^44/40Ca. Surface waters (P = pond) generally exhibited higher <em>δ</em>^44/40Ca than paired groundwaters (S = spring), consistent with preferential incorporation of light Ca isotopes during secondary CaCO₃ precipitation and enrichment of the residual water in heavier Ca isotopes. Enhanced aquatic photosynthesis increased DIC consumption, promoted CaCO₃ precipitation, and amplified the surface–groundwater Ca-isotope offset (Δ^44/40Ca _(P-S) = <em>δ</em>^44/40Ca _(P) − <em>δ</em>^44/40Ca _(S)). Land use further strengthened this offset by regulating both groundwater Ca²⁺ and DIC inputs (thereby influencing precipitation intensity) and primary productivity, following a gradient from bare rock to bare soil and vegetation cover. These findings highlight photosynthesis–driven carbonate precipitation as an important process shaping Ca-isotope variability in terrestrial carbonate watersheds.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 275-288"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148542159","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":"Controls on boron isotope ratios in marine bivalve shells: Insights from a controlled experiment across pH and temperature gradients","authors":"Diana L. Thatcher,&nbsp;Joseph A. Stewart,&nbsp;Michèle LaVigne,&nbsp;Branwen Williams,&nbsp;Nina M. Whitney,&nbsp;Maya Giss,&nbsp;Teagan McMahon,&nbsp;Brittany Jellison,&nbsp;Katherine Guay,&nbsp;Heidi Franklin,&nbsp;Alan D. Wanamaker","doi":"10.1016/j.gca.2026.04.035","DOIUrl":"10.1016/j.gca.2026.04.035","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Documenting spatial and temporal patterns of ocean acidification and understanding the way marine organisms build carbonate skeletons is critical to assessing their potential vulnerability to present and future stressors. The boron isotopic composition (δ&lt;sup&gt;11&lt;/sup&gt;B&lt;sub&gt;c&lt;/sub&gt;) of many marine carbonates provides insight into the pH at the site of calcification within biocalcifiers and, by extension, the pH of ambient seawater when the carbonate formed. The modification of seawater carbonate chemistry at the site of calcification by marine calcifiers and the utility of different taxa as paleo-pH proxy archives remains an area of active research. Despite the significance of marine bivalves to ecosystem function, high-resolution paleoclimatic studies, and the shellfish industry, their biocalcification mechanisms, controls on internal pH, and potential for reconstructing records of past seawater pH remain unclear. To address these gaps, a 20.5-week flowthrough tank experiment was conducted in which four species of commercially important bivalves from the northwest Atlantic Ocean were grown in tanks with controlled pH&lt;sub&gt;T&lt;/sub&gt; (pH 7.4 to 8.0) and temperature conditions (6 to 12 °C). A total of 106 shell samples from 99 individuals of adult and juvenile &lt;em&gt;Arctica islandica&lt;/em&gt; (ocean quahog), juvenile &lt;em&gt;Mercenaria mercenaria&lt;/em&gt; (northern quahog or hard clam), juvenile &lt;em&gt;Mya arenaria&lt;/em&gt; (soft-shell clam) and juvenile &lt;em&gt;Placopecten magellanicus&lt;/em&gt; (Atlantic sea scallop) were analyzed from this controlled experiment to assess the seawater pH, temperature, and growth rate controls on shell δ&lt;sup&gt;11&lt;/sup&gt;B&lt;sub&gt;c&lt;/sub&gt;.These four bivalve species, grown under identical, controlled conditions, showed differential responses to the same seawater temperature and pH, likely due to differences in how they regulate the pH of their internal fluids. Juvenile &lt;em&gt;P. magellanicus&lt;/em&gt; and juvenile &lt;em&gt;M. mercenaria&lt;/em&gt; demonstrated significant relationships (R≥0.60; &lt;em&gt;p-value&lt;/em&gt; &lt;0.006) between tank pH&lt;sub&gt;T&lt;/sub&gt; and δ&lt;sup&gt;11&lt;/sup&gt;B&lt;sub&gt;c&lt;/sub&gt;, suggesting potential utility as proxies for past ambient seawater pH. Conversely, the δ&lt;sup&gt;11&lt;/sup&gt;B&lt;sub&gt;c&lt;/sub&gt; of juvenile &lt;em&gt;A. islandica&lt;/em&gt; and juvenile &lt;em&gt;M. arenaria&lt;/em&gt; did not yield a strong relationship with seawater pH&lt;sub&gt;T&lt;/sub&gt; but instead yielded significant relationships with shell growth rate (linear extension), with a positive relationship for &lt;em&gt;M. arenaria&lt;/em&gt; and a negative relationship for juvenile &lt;em&gt;A. islandica&lt;/em&gt;. The δ&lt;sup&gt;11&lt;/sup&gt;B results from the few (n=9) adult &lt;em&gt;A. islandica&lt;/em&gt; shells measured show the most variability across the range of pH and temperatures (range of 16‰) and no significant relationship was found with seawater pH or growth rate. Despite rigorous oxidative cleaning of samples, the data suggest that adult &lt;em&gt;A. islandica&lt;/em&gt; shells contain boron-rich organic phases resistant to traditional cleaning techniques. This suggests t","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 143-159"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148541747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controls on Mg isotopic fractionation between deep mantle phases and relict signatures of a terrestrial magma ocean","authors":"Andrew M. Walker,&nbsp;Remco C. Hin,&nbsp;Tim Elliott","doi":"10.1016/j.gca.2026.04.030","DOIUrl":"10.1016/j.gca.2026.04.030","url":null,"abstract":"<div><div>We use density functional theory to investigate the fractionation of Mg isotopes between phases in the lower mantle. Our results support previous work and show that coordination number plays an important role in controlling isotopic fractionation, with bridgmanite (perovskite-structured MgSiO₃) preferentially incorporating lighter Mg isotopes into its highly coordinated site compared to periclase (MgO). Increasing pressure enhances this fractionation while increasing temperature decreases it. These two effects trade-off such that the preference is evident across all lower mantle conditions explored, even to the high temperatures of the chondritic liquidus (e.g. <span><math><msup><mrow><mi>Δ</mi></mrow><mrow><mn>26</mn><mo>/</mo><mn>24</mn></mrow></msup></math></span>Mg<span><math><msub><mrow></mrow><mrow><mi>Per−Bdm</mi></mrow></msub></math></span> is 0.04‰ at 4200 K and 87 GPa). In additional numerical experiments we separate the effect of coordination number from differences in bond length between different phases and these allow us to build an ionic model which parameterises magnesium isotope fractionation as a function of bond length, coordination number, and temperature. This model provides us with a preliminary means to describe isotope partitioning between solid and liquid phases when making predictions of Mg isotopic differences generated during terrestrial magma ocean crystallisation. We find that Mg isotopic fractionation between bridgmanite and melt, at lower mantle conditions, is sufficient to generate detectable differences in the Mg isotopic compositions of a residual melt or solid cumulate phase, relative to bulk Earth. More specifically, we show that isolation of a reservoir of cumulate bridgmanite that is some 3%–15% by mass of the mantle could account for the super-chondritic ²⁶Mg/²⁴Mg of accessible terrestrial peridotite samples. Whether such a reservoir can be dynamically preserved over Earth history remains an open question, but our results help quantify possible tests of such a scenario.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"425 ","pages":"Pages 131-142"},"PeriodicalIF":5.2,"publicationDate":"2026-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148542158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineral-associated organic carbon dominance and persistence in coastal wetlands","authors":"Yanqi Xiao,&nbsp;Steven J. Hall,&nbsp;Aaron Thompson,&nbsp;Jialin Wang,&nbsp;Jingxuan Chen,&nbsp;Yilin Lan,&nbsp;Cong-Qiang Liu,&nbsp;Chunmei Chen","doi":"10.1016/j.gca.2026.04.011","DOIUrl":"10.1016/j.gca.2026.04.011","url":null,"abstract":"<div><div>Coastal wetlands are vital global carbon reservoirs, yet the mechanisms governing the accrual and persistence of organic carbon (OC) remain unresolved. Through a continental-scale survey of China’s coastal wetlands (including saltmarshes and mangroves) combined with a global data synthesis, we demonstrated that coastal wetlands were overwhelmingly dominated by mineral-associated OC (MAOC), which constituted ∼ 73% of total OC—significantly more than in forests and peatlands. This MAOC showed no evidence of mineral saturation, underscoring its potential as an important repository for additional carbon storage. The OC content of the high-density (&gt;1.6 <!--> <!-->g<!--> <!-->cm⁻³) and fine-grained (silt + clay, &lt;53 <!--> <!-->μm) soil fraction (g C kg⁻¹ fraction), termed the dense/fine fraction, was driven by primary productivity, pH, and mineral specific surface area. Contrary to the prevailing assumption that both silt and clay promote MAOC, increasing silt content decreased specific surface area and diluted the OC content of the dense/fine fraction, while higher clay content provided greater surface area that enhanced OC accrual. MAOC persistence, measured by Δ¹⁴C, was primarily predicted by OC content of the dense/fine fraction, outweighing the influence of mineral attributes. Mean annual temperature was the second strongest predictor of MAOC persistence, with warmer climate leading to a larger but faster-cycling MAOC pool, highlighting a climatological temperature-driven trade-off between its accumulation and vulnerability. Saltmarshes—with lower MAOC content yet greater persistence and more abundant high-reactivity phyllosilicates than mangroves—may represent ideal targets for boosting carbon storage through increased OC inputs. Our findings establish the dominance and persistence of mineral-associated carbon in coastal wetlands and underscore their potential for targeted efforts to accrue and store carbon.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"424 ","pages":"Pages 257-270"},"PeriodicalIF":5.2,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681528","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":"Distribution and evolution of manganese minerals in polymetallic nodules from the Clarion-Clipperton Fracture Zone: implications for nickel and copper enrichment","authors":"Zedong Fan,&nbsp;Xiaohu Li,&nbsp;Yanhui Dong,&nbsp;Bruno Lanson,&nbsp;Zhongkuan Wu,&nbsp;Weilin Ma,&nbsp;Zhenggang Li,&nbsp;Junming Zhou,&nbsp;Yi Ding,&nbsp;Hao Wang,&nbsp;Zhimin Zhu,&nbsp;Jie Li,&nbsp;Xingwei Meng,&nbsp;Huaiming Li,&nbsp;Fengyou Chu","doi":"10.1016/j.gca.2026.04.016","DOIUrl":"10.1016/j.gca.2026.04.016","url":null,"abstract":"<div><div>Mn oxides in polymetallic nodules act as pivotal reservoirs for Ni and Cu, governing the biogeochemical cycling of these metals in marine environments. However, accurate identification of Mn-oxide phases—such as buserite, asbolane, and todorokite—remains challenging due to their similar X-ray diffraction characteristics. By applying an integrated mineralogical approach, this study elucidates the distribution and mineralogical controls of Ni and Cu in two diagenetic nodules from the Clarion-Clipperton Fracture Zone. Our results demonstrate a distinct mineralogical zonation: todorokite is predominantly concentrated in the inner layers (constituting up to ∼ 68% of the Mn-oxide assemblage), while the outer layers are dominated by 10 Å vernadite (buserite) and asbolane. XANES analysis reveals a significantly higher proportion of Mn(III) in the inner layers (15–25%) compared to the outer layers (8–10%). This Mn(III) enrichment, which we interpret as resulting from early nodule growth under high-productivity-driven suboxic conditions, likely promotes the transformation of 10 Å vernadite into todorokite. This mineralogical transition induces to a 40–50% decrease in Ni content in the inner layer, consistent with the lower compatibility of Ni in the todorokite structure. In contrast, Cu²⁺, as a Jahn–Teller active element, appears to be compatible with the todorokite structure and exhibits similar contents in both todorokite and asbolane. As nodule growth proceeds into more oxic environments, the Increased Stability of Mn(IV), most likely inhibited tectomanganate formation and may have favored the phyllomanganate stability. Furthermore, the precipitation metal (hydr)oxides in phyllomanganate interlayers could have led to the asbolane formation. Collectively, our findings underscore that fine-scale mineralogical characterization is indispensable for deciphering the distinct biogeochemical behaviors of Ni and Cu governed by specific Mn oxides.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"424 ","pages":"Pages 300-315"},"PeriodicalIF":5.2,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147736501","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}