Geochimica et Cosmochimica Acta最新文献

{"title":"Fractionation during sediment winnowing drives divergent mass accumulation rates derived from 230Th and 3He on the Cocos Ridge","authors":"Iva Tomchovska ,&nbsp;Frank J. Pavia ,&nbsp;Jess F. Adkins ,&nbsp;William M. Berelson ,&nbsp;Matthew P. Quinan ,&nbsp;Kenneth A. Farley","doi":"10.1016/j.gca.2025.02.021","DOIUrl":"10.1016/j.gca.2025.02.021","url":null,"abstract":"<div><div>We examine seven multicores obtained from the Cocos Ridge, including three potentially winnowed sites, and investigate how grain size fractionation affects ²³⁰Th_XS- and ³He_ET-derived mass accumulation rates (MARs). We find that bulk sediment ³He_ET-derived MARs are a factor of 1.5–4.1 higher than ²³⁰Th_XS-derived estimates in shallow winnowed sites, and 9–37 % lower than ²³⁰Th_XS-derived estimates at deeper sites. Concentration measurements of ²³⁰Th_XS and ³He_ET on multiple grain size fractions show that at winnowed sites, 41 % of the ³He_ET inventory and only 18 % of the ²³⁰Th_XS inventory is found in the smallest size class, while at deeper sites over 75 % of the total inventories of both proxies are in the &lt;<span><math><mrow><mn>20</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> fraction. The data demonstrates that ³He_ET is preferentially mobilized during sediment winnowing compared to ²³⁰Th_XS, which drives the observed discordance in proxy-derived MARs at sites that have experienced significant removal of fine-grained sediment.</div><div>Comparison of ²³⁰Th_XS and ³He_ET to lithogenic dust proxies indicate that ³He_ET remains unfractionated from dust, regardless of notable variations in winnowing and focusing. Likewise, ²³⁰Th_XS does not significantly fractionate from lithogenic proxies, with potential decoupling only observed in intensely winnowed sites. Biogenic silica exhibits behavior similar to dust. Constituent fluxes show less variability across core sites when using helium-derived MARs rather than thorium-derived MARs, suggesting that ²³⁰Th_XS and biogenic silica are differentially transported in winnowed locations. Conversely, thorium-derived MARs present a CaCO₃ flux profile that is more consistent across the cores, indicating that ²³⁰Th_XS remains largely unfractionated from CaCO₃ during winnowing. Thus, the preferred constant flux proxy in a winnowed site depends on the characteristics of the sedimentary component of interest. Additionally, the absence of fractionation of ³He_ET from terrigenous dust and its associated radiogenic ⁴He suggests that winnowing and focusing will not substantially modify ³He_/⁴He and ³He/(1-carbonate fraction) ratios, tracers used to identify longer term changes in the extraterrestrial ³He flux.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 149-165"},"PeriodicalIF":4.5,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143783601","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 “Kinetics of H2–O2–H2O redox equilibria and formation of metastable H2O2 under low temperature hydrothermal conditions” [Geochim. Cosmochim. Acta 75(6) (2011) 1594–1607]","authors":"Dionysis I. Foustoukos,&nbsp;Jennifer L. Houghton,&nbsp;William E. Seyfried Jr.,&nbsp;Stefan M. Sievert,&nbsp;George D. Cody","doi":"10.1016/j.gca.2025.02.009","DOIUrl":"10.1016/j.gca.2025.02.009","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Page 196"},"PeriodicalIF":4.5,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821322","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 13C–13C isotopologue signatures of thermogenic ethane","authors":"Koudai Taguchi ,&nbsp;Yuichiro Ueno ,&nbsp;Alexis Gilbert ,&nbsp;Yohei Matsui ,&nbsp;Takazo Shibuya ,&nbsp;Shinsuke Kawagucci","doi":"10.1016/j.gca.2025.02.017","DOIUrl":"10.1016/j.gca.2025.02.017","url":null,"abstract":"<div><div>The origin of hydrocarbons is a central question in climate science, biogeochemistry, and astrobiology. Carbon and hydrogen isotopic ratios have been used to constrain hydrocarbon sources; however, studies based on these parameters alone are lacking. The recent development of a doubly substituted (“clumped”) ethane isotopologue (¹³C₂H₆) is expected to be useful in distinguishing between thermogenic and abiotic ethane owing to the specific signature of the former. However, the mechanistic determinants of clumped ¹³C–¹³C isotopologue signatures in thermogenic ethane remain insufficiently understood. In this study, we conducted pyrolysis experiments over ∼ 2 years under controlled temperatures and pressures, with lignin, docosane (C₂₂H₄₆), and marine sediments used as reagents. All ethane samples exhibited clumped ¹³C–¹³C isotopologue signatures with similarly nearly absent or slight ¹³C–¹³C enrichment against a stochastic distribution. The ¹³C–¹³C clumping of thermally produced ethane from organic matter was similar to that of natural thermogenic ethane and different from that of putatively abiotic ethane of Kidd Creek and the Dingo gas field in the Amadeus Basin, which showed a significantly lower abundance of ¹³C–¹³C relative to stochastic distribution. The abundances of ¹³C–¹³C in ethane suggest that the signature of thermogenic ethane is inherited from a C–C bond in the precursor molecule and altered by a combinatorial effect during thermal cracking. Post-genetic ethane decomposition via heating might alter the ¹³C–¹³C signature in ethane, although the effects are difficult to observe. Thermogenic ethane should exhibit a positive clumped isotopologue signature regardless of thermal maturity; therefore, clumped isotopologue signatures may serve as key indicators to distinguish between thermogenic and abiotic ethane.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 258-267"},"PeriodicalIF":4.5,"publicationDate":"2025-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547108","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":"Proteinaceous deep sea coral amino acid isotope records reveal climate-driven decadal-scale planktic ecosystem fluctuations","authors":"Genevieve M. Pugsley ,&nbsp;Thomas P. Guilderson ,&nbsp;Danielle S. Glynn ,&nbsp;Yuan Shen ,&nbsp;Matthew D. McCarthy","doi":"10.1016/j.gca.2025.02.018","DOIUrl":"10.1016/j.gca.2025.02.018","url":null,"abstract":"<div><div>Decadal-scale climate variability drives important fluctuations in nutrient availability and productivity in highly productive eastern boundary current upwelling ecosystems, but the relatively brief duration of most monitoring efforts limits understanding of these dynamics. When applied to high-resolution paleoarchives such as deep-sea proteinaceous coral skeletons, stable carbon and nitrogen isotope (δ¹³C and δ¹⁵N) analysis can provide useful new insight into biogeochemical and ecological changes beyond the instrumental record. However, interpretation of bulk δ¹³C and δ¹⁵N records is often complicated by multiple possible drivers of variability. Here, we addressed these challenges by applying both bulk and compound-specific amino acid δ¹⁵N and δ¹³C analysis to two bamboo coral specimens from Sur Ridge on the central California margin, generating sub-decadal resolution records spanning c. 1810 to present. Our overarching goals were to first test amino acid δ¹³C and δ¹⁵N proxies in proteinaceous deep-sea bamboo coral archives, and second to investigate links between climate forcing and biogeochemical responses on the California margin over the Anthropocene.</div><div>Together, comparison of deep-sea coral amino acid trophic position results to local sediment traps and endmember mixing analysis indicate that bamboo coral feed directly on exported sinking particles, which are comprised primarily of zooplankton fecal pellets (&gt;70 %). This new evidence contradicts some past work based on bulk δ¹⁵N analysis alone and validates bamboo coral as archives of euphotic zone processes. Amino acid δ¹⁵N proxies also reveal that trophic position, not baseline δ¹⁵N of nitrate or phytoplankton production, is the primary driver of bulk δ¹⁵N variability in these coral records from a highly-productive coastal upwelling environment.</div><div>Our approximately 200-year reconstruction shows overall long-term ecosystem stability since the pre-industrial period, overlain by major multidecadal-scale fluctuations in bamboo coral trophic position and δ¹³C of primary production. Relatively high (low) trophic position and low (high) δ¹³C values of primary production occurred during negative (positive) phases of the Pacific Decadal Oscillation over the 20th century. Counter to expectations, these results suggest lower primary production likely occurred during past periods of high nitrate availability in our study region. Modern satellite chlorophyll-a observations corroborate this finding. We hypothesize that offshore transport and subduction of nutrients and phytoplankton and/or precipitation-mediated changes in iron availability may link climate variability and planktic ecosystem dynamics in this region.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 268-283"},"PeriodicalIF":4.5,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547109","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":"Near-equilibrium kinetics in the Fe(II)-silicate system and the significance of nanoparticle greenalite in Archaean Iron Formations","authors":"Serhat Sevgen ,&nbsp;Anika Retzmann ,&nbsp;Michael Nightingale ,&nbsp;Juan Carlos de Obeso ,&nbsp;Qin Zhang ,&nbsp;Ian Fleming ,&nbsp;Rosalie Tostevin ,&nbsp;Nicholas J. Tosca ,&nbsp;Benjamin M. Tutolo","doi":"10.1016/j.gca.2025.02.015","DOIUrl":"10.1016/j.gca.2025.02.015","url":null,"abstract":"<div><div>As the products of chemical sedimentation in the Archean oceans, Banded Iron Formations (BIFs) have been interpreted to record (bio)geochemical transitions in Earth’s ancient biosphere. Nonetheless, the effects of diagenesis and metamorphism over the long history of these rocks make it difficult to identify the minerals involved in the earliest stages of BIF formation. A series of recent studies has suggested that greenalite (Fe²⁺₃Si₂O₅(OH)₄), formed through hydrothermal fluid-seawater interactions, was among the primary mineral components of BIFs. However, the reactivity of greenalite as a function of relevant environmental parameters has not yet been mechanistically studied. The plausibility of its role in forming BIF deposits therefore remains speculative. Here, we fill this knowledge gap by conducting a series of kinetic experiments using a novel Si isotope doping method with hydrated, amorphous Fe(II)-silicate (a precursor to crystalline greenalite). The advantage of this technique is that it permits simultaneous determination of near-equilibrium forward and reverse reaction rates of Fe(II)-silicate-fluid interaction in plausible Archean ocean compositions. Reaction rate calculations indicate that the system’s behavior is governed by Fe(II)-silicate saturation state, with SiO₂ sorption becoming dominant once a saturation threshold is exceeded. Combining kinetic data and thermodynamic calculations for the Fe-silicate-seawater system permits determination of a new solubility product for amorphous Fe(II)-silicate as log(<em>K</em>) = 24.9 ± 0.25. This value indicates maximum Fe²⁺ concentrations in Archean ocean waters at 25 °C would range from ∼ 1 mmol/kg at pH 7 to ∼ 10 µmol/kg at pH 8. Combining these observations with calculations of Stokes’ settling velocity implies that long-distance transport of greenalite nanoparticles – <em>e. g.,</em> from deep-ocean hydrothermal vent sources to loci of BIF deposition – would have been feasible. Coupled with SiO₂ sorption behavior on greenalite surfaces and the background SiO₂ flux associated with the unique styles of Archean chert deposition, these results suggest that periodic waxing and waning of greenalite nanoparticle transport to BIF depositional environments can help to explain the Fe- and Si-enriched layers preserved in BIFs. Our results also provide a mechanistic underpinning for the exceptional preservation of greenalite in Archean sediments and its frequent association with chert. Ultimately, the readiness with which greenalite would have precipitated from Archean seawater and its apparent ability to be preserved despite transport across ocean basins suggests that it is time to reassess the traces of Earth’s early oceans recorded in BIFs and the ways in which these may be interpreted in light of new depositional models.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 135-148"},"PeriodicalIF":4.5,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143783600","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":"Rubidium isotopic compositions of the mantle sources of ocean island basalts","authors":"Baoliang Wang ,&nbsp;Frederic Moynier ,&nbsp;Matthew G. Jackson ,&nbsp;James M.D. Day","doi":"10.1016/j.gca.2025.02.011","DOIUrl":"10.1016/j.gca.2025.02.011","url":null,"abstract":"<div><div>Ocean island basalts (OIB) offer valuable insights into the chemical composition of Earth’s mantle. Distinct radiogenic isotope compositions recorded in OIB have been used to characterize diverse mantle sources, indicating the presence of recycled crustal components within plume sources. Rubidium isotopes have the potential to trace crustal recycling, given the significant enrichment of Rb in the crust relative to the mantle, and the inherent variability of Rb isotopes among crustal materials. Here we present Rb isotope data of twenty-eight OIB and two peridotite xenoliths representing EM1, EM2, HIMU, and FOZO mantle, with locations spanning the Pacific, Atlantic, and Indian Oceans. Except for one sample from Mangaia, which was affected by low-temperature alteration, the Rb isotopic compositions of remaining samples reflect the characteristics of their mantle source, exhibiting a δ⁸⁷Rb range of variations from −0.19 to +0.01 ‰. To a first order, the Rb isotopic similarity between OIB, peridotite xenoliths, and previously reported mid-ocean ridge basalts (MORB) suggests a relatively homogeneous Rb isotope composition of the mantle, displaying an average δ⁸⁷Rb value of −0.12 ± 0.09 ‰ (2SD, n = 52). Nevertheless, a discernible difference exists in primary lava compositions from Mangaia, with their Rb isotopic compositions (−0.02 ± 0.06 ‰, 2SD, n = 3) being 0.1 ‰ heavier than other OIB samples and the Bulk Silicate Earth (BSE) estimate. The heavy Rb isotope enrichment in Mangaia, the most extreme (highest ²⁰⁶Pb/²⁰⁴Pb) HIMU-type OIB examined in this study, is attributed to incorporation of high δ⁸⁷Rb signal within the mantle source, potentially due to the deep recycling of ancient altered oceanic crust.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 194-204"},"PeriodicalIF":4.5,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143496185","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":"Mg, Zn and Fe isotope evidence for derivation of K-rich basalts from the mantle hybridized by recycled carbonate-bearing silicate sediments","authors":"Zhao-Xue Wang ,&nbsp;Sheng-Ao Liu ,&nbsp;Dejan Prelević ,&nbsp;Shuguang Li ,&nbsp;Ze-Zhou Wang ,&nbsp;Tianhao Wu ,&nbsp;Jingao Liu","doi":"10.1016/j.gca.2025.02.016","DOIUrl":"10.1016/j.gca.2025.02.016","url":null,"abstract":"<div><div>Potassium-rich basalts provide valuable information about mantle heterogeneity and crust-mantle interaction because of their distinctive geochemical features. One of the long-standing issues regarding the origin of K-rich basalts is the nature of the K-rich mantle component required to generate such lavas. To provide further constraints on this issue, we present combined analyses of Mg, Zn and Fe isotopic compositions in the Cenozoic intraplate K-rich basalts from northeast China. The samples include both potassic and ultrapotassic basalts with K₂O/Na₂O ratios up to 3.42 and have typical Enriched Mantle-I Sr-Nd isotopic signatures. The ultrapotassic basalts have lighter Mg isotopic compositions than those of mid-ocean ridge basalts (MORB), but their Zn isotopic compositions are similar to or slightly higher than those of MORB, defining a strong Mg-Zn isotopic decoupling that suggests a dominant role of recycled carbonate-poor siliciclastic sediments in their sources. These rocks have Fe isotopic compositions (δ⁵⁶Fe) identical with those of MORB, indicating a peridotite-dominant source that has not been oxidized by the recycled sediments. Along with the high Fo (molar Mg²⁺/(Mg²⁺+Fe²⁺) × 100) of olivine phenocrysts, we suggest that the ultrapotassic basalts originated from the metasomatized (K-rich) sub-continental lithospheric mantle. Compared with ultrapotassic basalts, the potassic basalts have heavier Zn isotopic compositions at similar δ²⁶Mg, defining a weaker Mg-Zn isotopic decoupling that suggests a large proportion of carbonates in the recycled siliciclastic sediments (i.e., carbonate-rich sediments). In addition, the potassic basalts have higher δ⁵⁶Fe and lower Fo of olivine phenocrysts, pointing to a deeper, fertile mantle source that may have been oxidized by recycled carbonates, most likely at the mantle transition zone (MTZ). These results collectively suggest that both the potassic and ultrapotassic lavas in northeast China were formed via partial melting of the mantle hybridized by recycled siliciclastic sediments containing different proportions of carbonates. Therefore, the K-rich mantle component required for generating the extreme K enrichment in some intraplate lavas was primarily produced by recycled carbonate-bearing siliciclastic sediments in different mantle domains.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 244-257"},"PeriodicalIF":4.5,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143496184","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":"Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics","authors":"Antonia Klatt ,&nbsp;Cindy De Jonge ,&nbsp;Daniel B. Nelson ,&nbsp;Marta Reyes ,&nbsp;Carsten J. Schubert ,&nbsp;Nathalie Dubois ,&nbsp;S. Nemiah Ladd","doi":"10.1016/j.gca.2025.02.013","DOIUrl":"10.1016/j.gca.2025.02.013","url":null,"abstract":"<div><div>Reconstructions of past changes in algal community composition provide important context for future alterations in biogeochemical cycling. However, many existing phytoplankton proxies are indicative of individual algal groups and are not fully representative of the whole community. Here, we evaluated hydrogen isotope ratios of algal lipids (δ²H_Lipid) as a potential proxy for phytoplankton community composition. We sampled the water column of Rotsee, a small eutrophic lake in Switzerland, every second week from January 2019 to February 2020 and analyzed distributions and the relative offsets between δ²H_Lipid values (δ²H_{Lipid1/Lipid2}) from short-chain fatty acids, phytosterols and phytol. Comparing these data with phytoplankton cell counts, we found that δ²H_{C16:0 Acid/Sterol} and δ²H_{Sterol/Phytol} values reflect shifts within the eukaryotic algal community. To assess whether the selected phytoplankton groups were the main sources of the selected lipids, we further modeled algal δ²H_{Lipid1/Lipid2} values based on δ²H_{C16:0 Acid}, δ²H_Sterol and δ²H_Phytol values from batch cultures of individual algal groups and their biovolume in Rotsee and evaluated the role of heterotrophy on δ²H_{Lipid1/Lipid2} values using a model incorporating δ²H_{C16:0 Acid} and δ²H_Sterol values from microzooplankton. Annually-integrated and amount-weighted δ²H_{Lipid1/Lipid2} values measured in Rotsee were within 2 to 20 ‰ of the mean of modeled algal δ²H_{Lipid1/Lipid2} values, demonstrating a strong link with the phytoplankton community composition, while δ²H_{Lipid1/Lipid2} values including microzooplankton lipids had a larger offset. Additionally, cyanobacterial biovolume was positively correlated with the ratio of phytol and phytosterols (phytol:sterol ratio) as well as the ratio of unsaturated C18 and C16:0 fatty acids (C18:C16 ratio). Our results support the application of sedimentary δ²H_{Lipid1/Lipid2} values in eutrophic lakes as a proxy for past phytoplankton community assemblages. Moreover, the calculation of sedimentary phytol:sterol and C18:C16 ratios provides an additional proxy for reconstructing cyanobacterial blooms.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 205-219"},"PeriodicalIF":4.5,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547111","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":"Drivers of inorganic and organic carbon removal in aged oceanic crust","authors":"Sunita R. Shah Walter ,&nbsp;Leland J. Wood ,&nbsp;Kristin M. Yoshimura ,&nbsp;S.Fisher Gonski ,&nbsp;Wei-Jun Cai ,&nbsp;Julie A. Huber ,&nbsp;Elizabeth Trembath-Reichert ,&nbsp;Peter R. Girguis","doi":"10.1016/j.gca.2025.02.012","DOIUrl":"10.1016/j.gca.2025.02.012","url":null,"abstract":"<div><div>Large volumes of fluid flow through aged oceanic crust. Given the scale of this water flux, the exchange of organic and inorganic carbon that it mediates between the crust and deep ocean can be significant. However, off-axis carbon fluxes in older oceanic crust are still poorly constrained because access to low-temperature fluids from this environment is limited. At North Pond, a sedimented depression located on 8-million-year-old crust on the flank of the Mid-Atlantic Ridge, circulating crustal fluids are accessible through drilled borehole observatories. Here, fluids are cool (≤ 20 °C), oxygenated and bear strong geochemical similarities to bottom seawater. In this study, we report the concentrations and isotopic composition of dissolved organic and inorganic carbon from crustal fluids that were sampled six years after the installation of borehole observatories. These which better represent the fluid geochemistry prior to drilling and perturbation than earlier studies. Radiocarbon-based signatures within carbon reservoirs support divergent shallow and deep fluid pathways within the crust. We also report a net loss of both dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from the fluid during isolation in the crust. The removal of DOC is isotopically selective and consistent with microbe-mediated DOC oxidation. The loss of DIC is consistent with carbonate precipitation, although geochemical signatures of DIC addition to the fluids from DOC oxidation and basalt weathering are also evident. Extrapolated to global fluxes, systems like North Pond could be responsible for a net loss of ∼ 10¹¹ mol C yr⁻¹ of DIC and ∼ 10¹¹ mol C yr⁻¹ of DOC during the circulation of fluids through oceanic crust at low temperatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 1-14"},"PeriodicalIF":4.5,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143471430","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":"Corrigendum to “Fire distinguishers: Refined interpretations of polycyclic aromatic hydrocarbons for paleo-applications” [Geochimica et Cosmochimica Acta 289 (2020) 93–113]","authors":"A. Tyler Karp ,&nbsp;Alex I. Holman ,&nbsp;Peter Hopper ,&nbsp;Kliti Grice ,&nbsp;Katherine H. Freeman","doi":"10.1016/j.gca.2025.01.030","DOIUrl":"10.1016/j.gca.2025.01.030","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 277-278"},"PeriodicalIF":4.5,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143783090","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}