Geochimica et Cosmochimica Acta最新文献

{"title":"Oxygen and hydrogen isotope compositions in dentine collagen correlate strongly with oxygen isotope compositions of enamel carbonate","authors":"L.M. Reynard, M.J. Kohn","doi":"10.1016/j.gca.2025.05.009","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.009","url":null,"abstract":"The isotopic composition of tooth and bone has long been exploited in ecological, environmental, and archaeological studies. Increasingly, hydrogen and oxygen isotopes in collagen are used as tracers of environment and diet. However, the isotopic relationship between hydrogen and oxygen in collagen and oxygen in tooth enamel is poorly described. A new investigation of varied wild large herbivores shows that δ<ce:sup loc=\"post\">18</ce:sup>O and δ<ce:sup loc=\"post\">2</ce:sup>H in collagen are both strongly correlated to δ<ce:sup loc=\"post\">18</ce:sup>O in tooth enamel carbonate (r<ce:sup loc=\"post\">2</ce:sup> = 0.96 and r<ce:sup loc=\"post\">2</ce:sup> = 0.86, respectively), with a δ<ce:sup loc=\"post\">18</ce:sup>O collagen vs. δ<ce:sup loc=\"post\">18</ce:sup>O carbonate slope ∼ 0.8 and a δ<ce:sup loc=\"post\">2</ce:sup>H collagen vs. δ<ce:sup loc=\"post\">18</ce:sup>O carbonate slope ∼ 6. Given that enamel carbonate δ<ce:sup loc=\"post\">18</ce:sup>O generally reflects environmental water isotopic composition, δ<ce:sup loc=\"post\">2</ce:sup>H and δ<ce:sup loc=\"post\">18</ce:sup>O in collagen also reflect isotopic compositions in environmental water and may be used analogously to tooth enamel for environmental or dietary studies.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"9 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133759","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":"Compound class carbon isotope characterization of organic matter sources, transport, and degradation in sediments of large river-influenced coastal oceans","authors":"Fuqiang Wang, Shuwen Sun, Weikun Xu, Wenjing Fu, Honghua Shi, Meixun Zhao","doi":"10.1016/j.gca.2025.05.008","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.008","url":null,"abstract":"The Yangtze River Estuary and the adjacent inner shelf are significant areas for both the burial and degradation of terrestrial organic matter (OM). However, the impact of hydrodynamics on the degradation of different types of organic compound classes has not been fully elucidated. This study measured dual carbon isotopes (δ&lt;ce:sup loc=\"post\"&gt;13&lt;/ce:sup&gt;C, Δ&lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C) of organic compound classes [total hydrolysable amino acids (THAAs), total lipids, humic acids (HAs) and acid-base insoluble OM] in both surface and core sediment samples to evaluate the influences of hydrodynamic processes on the fates of organic compound classes in the Yangtze River Estuary and the adjacent inner shelf. In surface sediments, the δ&lt;ce:sup loc=\"post\"&gt;13&lt;/ce:sup&gt;C (−28.6 ± 0.6 ‰ in lipids; −21.8 ± 0.5 ‰ in THAAs) and Δ&lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C (−598 ± 41 ‰ in lipids; −143 ± 47 ‰ in THAAs) values of lipids and THAAs from the mobile-muds are lower than those from the offshore areas (δ&lt;ce:sup loc=\"post\"&gt;13&lt;/ce:sup&gt;C: −27.9 ± 0.4 ‰ in lipids; −20.9 ± 0.8 ‰ in THAAs; Δ&lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C: −559 ± 20 ‰ in lipids; −64 ± 7 ‰ in THAAs), indicating replenishment of marine source may be the primary factor contributing to the rejuvenation of lipids and THAAs during seaward transport. In contrast, both HAs and acid-base insoluble OM have higher Δ&lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C values in mobile muds (−298 ± 28 ‰ and −322 ± 21 ‰, respectively) than those in offshore areas (−443 ± 14 ‰ and −533 ± 30 ‰, respectively), suggesting significant aging even for the refractory OM during transport processes. The three end-member model of organic compound classes shows that lipids and THAAs in mobile-muds have higher marine source than offshore areas, while HAs show opposite change. These results indicate organic compound classes undergo different transport and degradation mechanisms during seaward transport, then affecting the contributions of marine and terrestrial sources to marine sediments. The different correlations between Δ&lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C values of labile (THAAs) and refractory (HAs and acid-base insoluble OM) OM with specific mineral surface areas (SSA) also indicate different transport and degradation mechanisms of organic compound classes in surface sediments, and causing rejuvenation of THAAs and gradually aging of HAs and acid-base insoluble OM during seaward transport. In core QT1 samples, the younger &lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C ages and large variations in the accumulation rates of labile THAAs since 2003 indicate that the construction of the TGD probably altered the hydrodynamic and depositional environment in these areas, and causing the degradation of THAAs in the sediment cores. In contrast, acid-base insoluble OM have stable &lt;ce:sup loc=\"post\"&gt;14&lt;/ce:sup&gt;C ages and accumulation rates in cores TQ1 and QT3, suggesting minor impacts from human activities and physical processes. These carbon isotopic results suggest th","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"74 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083377","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":"Tin isotope systematics in subduction zones","authors":"Xueying Wang ,&nbsp;Oliver Nebel ,&nbsp;Alexandra Churchus ,&nbsp;Peter A. Cawood","doi":"10.1016/j.gca.2025.05.004","DOIUrl":"10.1016/j.gca.2025.05.004","url":null,"abstract":"<div><div>The origin of slab components in arc lavas remains controversial with proposed sources including direct sediment melts, sediment-mantle mélanges, or crustal fluids. Stable isotope distributions of fluid-borne metals and those immobile in subduction components have the potential to trace the respective contribution of these components if placed into the context of additional magmatic differentiation and in conjunction with radiogenic isotopes. Here, we present the first high-precision double-spike tin abundances and isotope compositions in twenty-six arc rocks sampled along the Indonesian Sunda arc, a subduction zone with the highest subducted sediment volume globally. <em>δ</em>^122/118Sn_3161a in these samples ranges from 0.13‰ to 0.46‰ and we find that Sn isotope compositions in Sunda arc rocks were affected by magmatic differentiation, superimposed on additional influences from components derived from the subducting slab. A step change in <em>δ</em>^122/118Sn_3161a at 4–5wt.% MgO suggests the removal of heavier Sn isotopes, likely due to higher compatibility of isotopically heavier Sn⁴⁺ in Fe-Ti oxides along the liquid line of descent. This change of ∼0.1‰, however, is dwarfed by Sn isotope variations consistent with sediment melt contribution coupled with fluid addition from altered oceanic crust, both of which introduce lighter Sn isotopes. Sediment melt contamination increases with depth (temperature), but some exceptions at shallow sub-arc sources (depth ≤ 130 km) indicate additional melting of a mélange-style source. Our findings suggest the coexistence of mélange contributions, and deep fluid-induced melting plus partial sediment melts in the Sunda arc. Mélanges contribute only at shallow depths (≤130 km), consistent with their diapiric nature, whereas deeper levels favor fluid-fluxed melting and, at higher temperatures and pressures, partial sediment melting. This study provides insights into the complex interactions between fluids, sediments, and mantle wedge in subduction zones, highlighting the depth-dependent nature of slab contributions to arc magmatism. It also demonstrates the utility of Sn isotopes for tracing these processes and advancing our understanding of subduction zone geochemistry.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 18-34"},"PeriodicalIF":4.5,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143947247","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":"Large Zn isotope variations in lower oceanic crust offer insights into oceanic crustal magma plumbing system","authors":"Wei-Qi Zhang, Chuan-Zhou Liu, Zong-Qi Zou, Xiao-Ni Li","doi":"10.1016/j.gca.2025.05.005","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.005","url":null,"abstract":"Constraining mid-ocean ridge magmatic processes is crucial for understanding the geochemical evolution of magmas traversing the oceanic crust. A crucial archive for investigating these magmatic processes is the chemical composition of lower oceanic crust. This study presents Zn isotope data for primitive to highly evolved cumulates from the Mid-Atlantic Ridge (Kane) and the Southwest Indian Ridge (IODP Hole U1473A), which are compared with published mid-ocean ridge (MOR) lava data. Previous studies have indicated that high-degree magma differentiation results in small Zn isotope fractionation (&lt;0.1 ‰) in the mafic to felsic MOR lavas. Unlike the MOR lavas, significant δ<ce:sup loc=\"post\">66</ce:sup>Zn variations (0.1 − 0.5 ‰) are observed in the Kane and U1473A cumulates, which cannot be explained by crystal accumulation alone but reflect the variable incorporation of trapped melts. These trapped melts exhibit heavy δ<ce:sup loc=\"post\">66</ce:sup>Zn (&gt;0.5 ‰) and strongly fractionated trace element characteristics, indicative of extensive melt-rock interactions. Furthermore, the bulk normal mid-ocean ridge basalt (N-MORB)-type lower oceanic crust has δ<ce:sup loc=\"post\">66</ce:sup>Zn values (0.24 ± 0.11 ‰) that are close to the average N-MORB (0.26 ± 0.06 ‰), suggesting minor Zn isotope fractionation during the crustal processing of MOR lavas. It is proposed that the small δ<ce:sup loc=\"post\">66</ce:sup>Zn variations in MOR magmas result from the homogenization and dilution of reactive signals within the eruptive reservoir. In contrast, prolonged processing of trapped melts through melt-rock interactions leads to significant Zn isotope fractionation in the lower oceanic crust. Thus, the evolution of oceanic crustal magma plumbing systems is more complex than inferred from MORB alone. Despite these complexities, efficient homogenization within eruptive reservoirs results in limited Zn isotopic variations in the erupted magmas. Hence, the Zn isotopic variations in MORB, except for the highly evolved ones, are predominantly linked to the source heterogeneity. Our findings also suggest heterogeneous δ<ce:sup loc=\"post\">66</ce:sup>Zn in subducted oceanic crusts, which has implications for mantle Zn isotope heterogeneity.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"77 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083378","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":"Combined Ca, Sr isotope and trace element analyses of Late Cretaceous dinosaur teeth: assessing diet versus diagenesis","authors":"Mateusz M. Michailow, Federico Lugli, Anna Cipriani, Francesco Della Giustina, Annalisa Ferretti, Daniele Malferrari, Denver Fowler, Elizabeth Freedman Fowler, Michael Weber, Thomas Tütken","doi":"10.1016/j.gca.2025.05.006","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.006","url":null,"abstract":"The Sr and Ca isotope composition, along with trace element content in fossil teeth, provides valuable insights into biogenic and diagenetic processes. Identifying pristine biological signals is crucial for reconstructing the diet and trophic levels of extinct taxa. We present novel geochemical data from Tyrannosauridae and Ceratopsidae teeth of the Late Cretaceous, using radiogenic Sr (<ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr), stable Sr (<ce:italic>δ</ce:italic><ce:sup loc=\"post\">88/86</ce:sup>Sr), and Ca (<ce:italic>δ</ce:italic><ce:sup loc=\"post\">44/42</ce:sup>Ca) isotopes, along with trace elements abundances to differentiate biogenic signals from diagenetic alteration.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"45 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133760","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":"Coprecipitation of phosphate with calcite: Molecular-scale evidence for incorporation and inclusion mechanisms","authors":"Chao Ren ,&nbsp;Yongfang Li ,&nbsp;Shaofeng Wang ,&nbsp;Jingzhao Wang ,&nbsp;Junfeng Ji ,&nbsp;Henry H. Teng ,&nbsp;Brian L. Phillips ,&nbsp;Kideok D. Kwon ,&nbsp;Wei Li","doi":"10.1016/j.gca.2025.04.032","DOIUrl":"10.1016/j.gca.2025.04.032","url":null,"abstract":"<div><div>Coprecipitation of phosphate in calcium carbonate minerals is a ubiquitous geochemical phenomenon in marine sedimentation and cave stalagmite formation, however, it is not clear whether phosphate is incorporated into the calcite structure. In this research, we applied solid-state nuclear magnetic resonance (NMR) spectroscopy to analyze P speciation during coprecipitation with calcite. The ³¹P NMR results show three peaks with chemical shifts of 3.9, 3.0 and −1.0 ppm, indicative of at least three phosphate species in the coprecipitates. Combined with advanced ³¹P{¹H} cross-polarization (CP)/MAS, ¹H DE/MAS, ³¹P{¹H} 2-d heteronuclear correlation (HetCor) and ³¹P{¹³C} cross-polarization rotational echo double resonance (CP-REDOR) NMR experiments, the 3.9 ppm peak can be tentatively assigned to calcite structural defects as amorphous calcium phosphate (ACP)-like environments while the 3.0 ppm peak arises from a carbonated hydroxyapatite (CHap). The ³¹P NMR peak at −1.0 ppm can be assigned to structurally incorporated phosphate in the calcite crystals in the form of HPO₄²⁻. Nano secondary ion mass spectrometry (NanoSIMS) and high-resolution scanning transmission electron microscopy (HR-STEM) analysis further suggests that the incorporated HPO₄²⁻ substitutes for the structural carbonate group (CO₃²⁻) of calcite. However, the local expansion stress field generated with HPO₄²⁻ incorporation in the calcite structure prevents PO₄/CO₃ isomorphous substitution and favors the precipitation of calcium phosphates. The findings of this study not only provide deep insights into carbonate crystal chemistry but also shed light on the application of carbonate materials as potent geochemical proxies in paleoenvironmental reconstructions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143922530","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":"238U/235U isotopic variations in angrites and their constituent minerals","authors":"Magdalena H. Huyskens ,&nbsp;Yuri Amelin ,&nbsp;Qing-Zhu Yin ,&nbsp;Tsuyoshi Iizuka","doi":"10.1016/j.gca.2025.04.030","DOIUrl":"10.1016/j.gca.2025.04.030","url":null,"abstract":"<div><div>Ages of angrites, a diverse and rapidly growing group of differentiated meteorites, are important for understanding the history of their parent body, which is proposed to be an archetypal first-generation planetesimal. Angrites also commonly serve as a time reference in the early Solar System chronology. Pb-isotopic ages of angrites can be determined with high precision, and the isotopic composition of uranium thus becomes a major contributor to the age accuracy and its total uncertainty budget. Two main groups of angrites, the rapidly cooled (volcanic and/or impact-generated) and plutonic angrites, were previously found to contain uranium with different ²³⁸U/²³⁵U ratios. The variations in isotopic compositions between mineral carriers of uranium within individual angrites, which are directly relevant to calculation of accurate Pb-isotopic ages, have not been studied yet. In this study, we determined the ²³⁸U/²³⁵U for whole rocks, leachate and residue of whole rocks and mineral separates for two rapidly cooled angrites D’Orbigny and Sahara 99555 and three plutonic angrites NWA 4801, NWA 4590 and Angra dos Reis. For the rapidly cooled angrites, all mineral separates as well as the whole rocks show consistent ²³⁸U/²³⁵U. Whole rock ²³⁸U/²³⁵U ratios for the plutonic angrites are distinctly lower than the ratios in the rapidly cooled angrites. In Angra dos Reis and NWA 4590, merrillite has higher ²³⁸U/²³⁵U than pyroxene, and both minerals have higher ²³⁸U/²³⁵U ratios than the respective whole rock, suggesting the presence of an unidentified mineral host of uranium with lower ²³⁸U/²³⁵U. These differences in U isotope composition could be possibly attributed to a combination of mass dependent and mass-independent isotope fractionation driven by the differences of oxidation state, and coordination in the crystals. We recalculated the existing Pb-isotopic dates when possible with the measured ²³⁸U/²³⁵U for the minerals that were used for the Pb-isotopic dating. The differences in U isotopic composition between cogenetic minerals point to the importance of ²³⁸U/²³⁵U determination in specific minerals that are used for Pb-isotopic dating for plutonic achondrites, rather than U isotopic data for bulk meteorites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 205-220"},"PeriodicalIF":4.5,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083379","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":"Thallium cycling and boundary exchange in a continental margin basin","authors":"Kasper P. Olesen ,&nbsp;Sune G. Nielsen ,&nbsp;Chadlin M. Ostrander ,&nbsp;Nicol Udy ,&nbsp;Donald E. Canfield","doi":"10.1016/j.gca.2025.04.005","DOIUrl":"10.1016/j.gca.2025.04.005","url":null,"abstract":"<div><div>Thallium (Tl) isotopes are a robust tracer of ancient ocean oxygenation through their link to the burial flux of deep-sea manganese oxide minerals. Yet, the details of Tl geochemistry at the continental margin remain largely unexplored, hindering quantitative application of the palaeoredox proxy. To develop our understanding of Tl diagenesis, phase dynamics, and mass transfer at the continent-ocean interface, we collected sediments from three sites in the perenially oxic Skagerrak sea as well as sediments and suspended particles from five adjacent rivers. The three Skagerrak sediment sites are biogeochemically diverse, with variable oxygen penetration (9–18 mm) and C-oxidation occurring predominantly through either sulfate, iron, or manganese reduction. Sequential extractions and porewater analyses reveal a highly homogeneous abundance and phase association pattern of Tl across all sample types and sites. Sediment and particle Tl resides almost exclusively in acid-leachable aluminous clays and residual crystalline phases. We interpret these phases to be terrigenous, except at the highly Mn-enriched site S9 where we find up to ∼45 % of Tl is authigenic. This claim is supported by Tl isotopic compositions of acid-leachable sediment (ε²⁰⁵Tl_HNO3), which average –2.5 ± 0.9‱, within uncertainty of the average upper crust value of –2.0 ± 0.5‱ and a regional riverine particle delivery value of –2.1 ± 1.2‱.</div><div>Incubations of Skagerrak sediments with added bottom water Tl reveal a fractionation factor (α) of ∼1.0007, amounting to an isotope ratio difference of ∼7‱. A comparable fractionation of 2.4 to 4.5‱ is calculated for authigenic Tl removal in the Skagerrak sediments. However, this fractionation is lower than that observed in deep sea pelagic clays and hydrogenetic Mn crusts and nodules (α ∼1.0021), yet significantly higher than expected for mature diagenetic Mn oxides like triclinic birnessite and todorokite (α ∼1.00005). Thallium cycling is largely decoupled from Mn diagenesis at our marine sites and only associates weakly with the active sedimentary Mn recycling. Rather, effluxing of dissolved Tl is observed at all sites. We employ a diagenetic reaction-transport model to quantify dissolved Tl fluxes and compare these fluxes with independent assessments of Tl mass balance based on authigenic/terrigenous Tl proportions. We find that within the oxic Skagerrak basin, sediments may be both true sources and, if Mn-enriched, true sinks of Tl, with extrapolated flux magnitudes relevant to marine Tl mass balances. Our study presents a much-needed description of Tl diagenesis in diffusive margin sediments and suggests that hitherto unrecognized sources of originally terrigenous Tl to the marine environment may occur at the continent-ocean boundary, either via the release of labile clay-bound Tl directly from riverine particles or during sediment diagenesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 64-81"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083381","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":"Strong depth-dependent chemical and structural characteristics of dissolved organic matter (DOM) in organic-rich sediment in a shallow temperate lake","authors":"Chenhui Wei ,&nbsp;Shu Tao ,&nbsp;Patrick G. Hatcher ,&nbsp;Dongqiang Zhu","doi":"10.1016/j.gca.2025.05.002","DOIUrl":"10.1016/j.gca.2025.05.002","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Porewater dissolved organic matter (DOM) in lake sediments is an important contributor to the global carbon cycle. The composition and structures of porewater DOM typically vary with depth, yet the variations in high-resolution depth intervals and the controlling biogeochemical processes are not well understood. Here we performed comprehensive, high-resolution (1 cm interval) characterization of sediment porewater DOM in Baiyangdian, a representative large shallow freshwater lake with abundant biomass deposition in northern China in the temperate zone, by employing chemical analysis, optical techniques, stable isotope analysis, ultra-high resolution mass spectrometry, and 16S rRNA gene sequencing. &lt;em&gt;Anaerolineaceae&lt;/em&gt; was the dominant microorganism in the sediment, reflecting fermentation as the key process involved in organic matter diagenesis. Contrasting &lt;sup&gt;13&lt;/sup&gt;C signatures between particulate organic matter (POM) and DOM suggest that selective degradation of organic matter with component-specific isotopic signatures at distinct depths is occurring. Corresponding to the concentration depth profile of POM, the composition and structures of DOM exhibited strong multilayered variations across the depths of 1–4 cm (surface layer), 5–13 cm (middle layer), and 14–19 cm (bottom layer). In the surface layer, intense fermentation of fresh POM rapidly released protein-like fluorescent components whose content decreased with depth, whereas humic-like fluorescent components gradually accumulated. Consistently, the aromaticity and molecular weight of chromophoric DOM analyzed by ultraviolet–visible spectroscopy increased with depth. Due to the exhaustion of labile POM and the decreased fermentation activity, the contents of protein-like and humic-like fluorescent components as well as the aromaticity and molecular weight of chromophoric DOM stayed relatively constant in the middle layer. In the bottom layer, the sharp increase in concentrations of dissolved organic carbon and volatile fatty acids (acetate, propionate, and butyrate) indicated re-enhanced fermentation activity, which was also supported by the prominent decrease in the protein-like and humic-like fluorescents as well as the decrease in aromaticity and molecular weight of chromophoric DOM. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed that the surface layer had the highest relative abundance of aliphatic compounds among the three layers, while aromatics and polycyclic aromatics accumulated only in the surface layer and middle layer, indicating their preferential production and consumption during POM deposition. However, lignin-like compounds accumulated gradually and consistently across the three layers, resulting from their refractory nature and continuous degradation of residual POM. Most of the N/S-containing molecules accumulating in the three layers were lignin-like, aromatic, and polycyclic aromatic compounds, which were appar","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 242-256"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083380","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":"Corals feel the water chemistry: trace elements in coral skeletons reflect accurately their seawater chemistry, biological and geochemical implications","authors":"Sharon Ram, Jonathan Erez","doi":"10.1016/j.gca.2025.05.003","DOIUrl":"https://doi.org/10.1016/j.gca.2025.05.003","url":null,"abstract":"The incorporation of trace and minor elements into coral skeletons and the underlying chemical and biological processes that govern them, are highly relevant for understanding coral biomineralization and for accurate reconstructions of past ocean conditions. In the present experimental study, that follows our previous publications (Ram and Erez, 2021, 2023), we determined the partition of six cations (Li, Na, Mg, K, Sr and Ba) into corals skeletons by culturing nine hermatypic coral species in seawater with four different calcium concentrations (∼ 10,15, 20 and 25 mM). The cation to Ca ratios in the skeletons correlated linearly with their ratios in seawater, revealing consistent and species-specific partition coefficients (D<ce:inf loc=\"post\">Coral</ce:inf>). Consistent with our previous work, we find that the partition coefficients for Li, Mg, Na, and K were significantly lower than one but higher than the inorganic values (D<ce:inf loc=\"post\">Inorg</ce:inf>), while for Sr and Ba, D<ce:inf loc=\"post\">Coral</ce:inf> were higher than one but lower than D<ce:inf loc=\"post\">Inorg</ce:inf> values. In addition, D<ce:inf loc=\"post\">Coral</ce:inf> for the elements with D<ce:inf loc=\"post\">El</ce:inf> &lt; 1, showed significant inter-species systematic order, with the highest D<ce:inf loc=\"post\">Coral</ce:inf> for <ce:italic>A. lamarcki</ce:italic>, corresponding to its highest calcification rates, whereas <ce:italic>P. damicornis</ce:italic> showed the lowest D<ce:inf loc=\"post\">Coral</ce:inf> values, consistent with its lowest calcification rates. The opposite systematic trend was observed for the elements with D<ce:inf loc=\"post\">El</ce:inf> &gt; 1. We attribute these systematic relationships between elemental partitioning and calcification rates to species-specific physiological control, indicating precipitation of the skeleton from a semi-closed seawater reservoir. The modified seawater that comprises this extracellular calcifying fluid follows Rayleigh distillation with respect to all the measured trace and minor elements. The level of Ca utilization (1-f) and the degree of isolation of the calcifying fluid from external seawater, control the efficiency and rate of the calcification. Given the consistent D<ce:inf loc=\"post\">Coral</ce:inf> values observed across all Ca treatments (for all elements and all coral species) we conclude that kinetic effects on the partition coefficients were unlikely. The deviations from D<ce:inf loc=\"post\">Inorg</ce:inf> values (the so-called “vital effect”) are governed by the physiology of the calcification process, involving mainly pH and DIC elevation in the ECF that is well known for corals. In addition, the present study provides a strong basis for utilizing multi-elemental proxies in fossil corals for reconstructing past ocean chemistry and climate changes during the Cenozoic era and possibly beyond, well into the Mesozoic.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"133 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133761","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}