Geochimica et Cosmochimica Acta最新文献

{"title":"Co-adsorption of phosphate and rare earth elements (REEs) on goethite induce middle REE-enriched fractionation","authors":"Xiaoju Lin ,&nbsp;Wenbin Yu ,&nbsp;Xiaoliang Liang ,&nbsp;Yoshio Takahashi ,&nbsp;Jingwen Zhou ,&nbsp;Yiping Yang ,&nbsp;Meng Chen ,&nbsp;Jianxi Zhu ,&nbsp;Runliang Zhu ,&nbsp;Hongping He","doi":"10.1016/j.gca.2025.08.027","DOIUrl":"10.1016/j.gca.2025.08.027","url":null,"abstract":"<div><div>As prominent geochemical tracers, rare earth elements (REEs) can be scavenged by Fe (hydr)oxides that are ubiquitous in supergene environments, profoundly altering the enrichment and fractionation behaviors of REEs. In light of the particle-reactive nature, high affinity for adsorption onto Fe (hydr)oxides, as well as strong complexation with REEs, phosphate probably affects the mobility and fractionation of REEs on Fe (hydr)oxides. This issue has yet been poorly understood. Herein, the co-adsorption of phosphate and REEs on goethite was studied at different phosphate concentrations and pH. The batch adsorption results show that phosphate shifted the pH adsorption edge of REEs on goethite to lower values, and thus enhanced the REE adsorption. Such positive effect became more pronounced with the increase of phosphate concentration. Interestingly, the presence of adsorbed phosphate altered the fractionation patterns of REEs, from heavy REE (HREE, Ho-Lu)-enriched pattern to a middle REE (MREE, Sm-Dy)-enriched one, which was intensified with the increase of phosphate concentration, especially at acidic pH. The adsorption geometries and energies were further investigated through <em>in situ</em> attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) combined with two-dimensional correlation analysis (2D-COS), density functional theory (DFT) and surface complexation model (SCM). The enhancement of REE adsorption by phosphate is ascribed to the formation of ternary inner-sphere complexes, where phosphate served as a bridge between REEs and goethite surface. At pH 5, phosphate formed mono-protonated bidentate binuclear phosphate complexes (Fe₂O₂POOH, MBB). Then, REEs (e.g., Sm) were bonded to the oxygen atom of phosphate by displacing an H atom in the MBB phosphate complexes, and ultimately forming monodentate ternary complexes (MT, Fe₂O₂POOSm). But at pH 7, the MT complexes were initially formed and then transformed into bidentate ternary complexes (Fe₂O₂PO₂Sm, BT), where Sm atom was concurrently bonded to two oxygen atoms in the phosphate complexes. These adsorption configurations were verified by DFT computations, as the adsorbed phosphate decreased the adsorption energy of REEs on goethite to form ternary complexes. Moreover, MREEs (e.g., Sm) formed the more stable ternary complexes than light REEs (LREEs, e.g., La) and HREEs (e.g., Lu). Thus, the formation of ternary complexes accounts for the phosphate-induced enrichment of MREEs. This study elucidates the molecular-level mechanisms governing the co-adsorption of phosphate and REEs on goethite and holds significant geochemical implications, including a novel perspective in understanding the enrichment patterns of MREEs in natural terrestrial waters.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 67-80"},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144901900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithium isotope fractionation between mica, quartz, amphibole, feldspars, and granitic melt: Experimental approach and implications for natural granitic systems","authors":"Xu Gao ,&nbsp;Julie Anne-Sophie Michaud ,&nbsp;Lennart Koch ,&nbsp;Zhenhua Zhou ,&nbsp;Chao Zhang ,&nbsp;Ingo Horn ,&nbsp;Renat R. Almeev ,&nbsp;Stefan Weyer ,&nbsp;François Holtz","doi":"10.1016/j.gca.2025.08.028","DOIUrl":"10.1016/j.gca.2025.08.028","url":null,"abstract":"<div><div>Lithium isotope fractionation has been extensively used to investigate magmatic and hydrothermal processes over the past decade. Thus, knowledge of Li isotope fractionation factors between minerals and melts is essential for the interpretation of Li isotope data. However, Li isotope fractionation between granitic melts and common silicate minerals has not been directly determined experimentally. To address this issue and to investigate the effect of NaCl-bearing fluids on lithium isotopic fractionation, we conducted Cl-free and Cl-bearing experiments aimed at investigating the isotope fractionation factors between silicate minerals and hydrous melt at 575 − 600 °C and 200 MPa. The run products are composed of Li-mica, K-rich feldspar, Na-rich feldspar, ferroholmquistite (Fhlm; a Li-bearing amphibole), quartz, and melt. In Cl-free experiments, quartz is isotopically heaviest with Li isotope fractionation between quartz and melt <em>Δ</em>_Qz-melt = +7.0 ‰ (translating to an isotope fractionation factor α = 1.0070), followed by Li-mica with <em>Δ</em>_Li-mica-melt = +3.1 ‰ (α = 1.0031), K-rich feldspar with <em>Δ</em>_K-fsp-melt = +0.1 ‰ (α = 1.0001), ferroholmquistite with <em>Δ</em>_Fhlm-melt =  − 1.9 ‰ (α = 0.9981) and Na-rich feldspar with <em>Δ</em>_Na-fsp-melt =  − 2.7 ‰ (α = 0.9973). Our experimental data indicate that Li-mica has a higher δ⁷Li value than granitic melt. This observation differs from previous findings, based on bond-energy estimations, according to which micas are expected to be isotopically lighter than the coexisting melt. This discrepancy may be attributed to the coordination environment in minerals, which can be distorted, influencing Li-O bonding energies. The Li isotope fractionation factors between mica, K-rich feldspar, Na-rich feldspar, ferroholmquistite, and melt in Cl-bearing experiments are very similar to those of Cl-free systems. This implies that the presence of NaCl-bearing fluids in a closed magmatic system has a limited effect on Li isotope fractionation during magmatic processes.</div><div>The results from a multi-stage quantitative fractionation model suggest that granitic residual melts evolve to isotopically lighter δ⁷Li values during crystal fractionation due to the high α_mica-melt and α_quartz-melt values (&gt;1). A high degree of crystal fractionation in Li-poor muscovite-bearing granitic systems could lead to a limited but still measurable Li isotope shift in residual melts (&gt;1‰), whereas shifts up to 6 ‰ are observed in Li-rich systems. Lithium-rich mica is thus more effective in causing Li isotope fractionation as compared to muscovite and biotite. Our findings imply that large lithium isotopic fractionation observed in natural granitic systems could be caused by magmatic processes, even if water–rock interaction in an open system does not occur.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 12-31"},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900803","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":"Potassium isotopic equilibrium fractionation induced by clay adsorption and incorporation: A density functional theory study","authors":"Yin-Chuan Li ,&nbsp;Hao-Long Li ,&nbsp;Hai-Zhen Wei ,&nbsp;Martin R. Palmer ,&nbsp;Yong-Hui Li ,&nbsp;Ya-Ru Zhou","doi":"10.1016/j.gca.2025.08.026","DOIUrl":"10.1016/j.gca.2025.08.026","url":null,"abstract":"<div><div>Chemical weathering of continental silicate rocks is a key process in controlling the concentration and isotope composition of many elements in seawater, including potassium. K isotopes show great potential for tracing the silicate weathering. However, their application remains constrained by a lack of understanding of K isotopic fractionation mechanisms during chemical weathering, wherein secondary clay minerals adsorb and incorporate K derived from silicate minerals. Using first-principles molecular dynamics simulations and density functional theory (DFT) calculation, the coordination states of K in aqueous fluid and at the kaolinite (001) and (010) surfaces, as well as the K isotopic equilibrium fractionation caused by the adsorption of kaolinite surface and the incorporation of illite and glauconite, have been investigated. The results show that five (^VK) and six (^VIK) coordinated K dominate in aqueous fluids (∼88 %) and on kaolinite (001) (∼84 %), while ^IVK and ^VK prevail on (010) surfaces (∼80 %). The 1000lnβ values of aqueous fluids and kaolinite (001) and (010) surface configurations do not correlate well with structural factors (e.g., K–O bond lengths, the distortions of K–O bond length and O–K–O angle of coordination polyhedral). Rather, the 1000lnβ values exhibit a strong linear correlation with the force constants acting on the K⁺ ion in minerals and fluids. This process results in K isotopic equilibrium fractionation between the kaolinite (001) and (010) surfaces and aqueous fluids of 0.63 ± 0.37 ‰ and 0.58 ± 0.42 ‰, respectively, at 25 °C. The tetrahedral Al absence alters the K isotope equilibrium fractionation between clay minerals and aqueous fluids (0.25 ± 0.30 ‰ vs. −0.37 ± 0.24 ‰ for illite; −0.06 ± 0.22 ‰ vs. −0.35 ± 0.23 ‰; for glauconite; at 25 °C). These theoretical calculations may be used to model K isotope evolution in surface weathering environments to gain a more detailed understanding of K isotope fractionation under varying conditions of temperature, pH, ionic strength, and salinity.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 32-46"},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900805","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":"Iron and zinc isotopes constrain the continental crust formation","authors":"Jianfeng Ma ,&nbsp;Hamed Gamaleldien ,&nbsp;Sheng-Ao Liu ,&nbsp;Yuan-Ru Qu","doi":"10.1016/j.gca.2025.08.024","DOIUrl":"10.1016/j.gca.2025.08.024","url":null,"abstract":"<div><div>The origin of Earth’s earliest felsic melts from mafic crust is still controversial. Their formation likely involved hydrothermal alteration of mafic protoliths followed by partial melting. However, the specific mechanisms and conditions of anatexis remain unclear. Investigating modern analogues like plagiogranites may offer key insights into the formation and evolution of the Earth’s early juvenile continental crust. Stable isotopes of iron (Fe) and zinc (Zn) are sensitive to chemical dynamic conditions and do not evolve with time, making them highly promising tracers for deciphering the origin of plagiogranites. Here, we present high-precision Fe-Zn isotope analysis and thermodynamic modeling to explore the formation of the El-Shadli plagiogranite complex in the Arabian-Nubian Shield as an example. These plagiogranite rocks have low Sr/Y (0.4–5.3) characteristics and exhibit a range of Fe-Zn isotopic compositions, with δ⁵⁶Fe values of 0.06 ± 0.04 ‰ to 0.19 ± 0.02 ‰ (2SD) and δ⁶⁶Zn values of 0.27 ± 0.03 ‰ to 0.41 ± 0.04 ‰ (2SD). Thermodynamic modeling indicates that H₂O-saturated melting of altered oceanic crust (AOC) at shallow crustal depths (2–6 kbar) and elevated temperatures (700–900 °C) with geothermal gradients of 1200–4500 °C/GPa under a mantle plume setting was the primary mechanism driving plagiogranite formation. Sub-mantle oxygen isotopes in zircon (δ¹⁸O from 4.06 ± 0.17 ‰ to 5.09 ± 0.20 ‰) indicate that the required fluid originated from seawater and regulates the partial melting of plagioclase and amphibole during anatexis, directly influencing Fe-Zn isotope fractionation between the resulting plagiogranite melts and their residual source. Notably, the 4.02 billion years (Ga) Idiwhaa gneisses share similar Fe isotope and trace element compositions with the El-Shadli plagiogranites, suggesting that the Earth’s earliest felsic continental crust may have formed through a comparable process. Thermodynamic modeling also indicates that the Idiwhaa gneisses originated from partial melting of an AOC-like protolith under a high thermal gradient of 1270–4100 °C/GPa, possibly in the context of a mantle plume or meteorite impact. Our findings underscore the effectiveness of Fe and Zn isotopes in tracing the genesis of felsic magmas and emphasize their promise in probing the evolution of the Early Earth’s continental crust.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 1-11"},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900804","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":"Drivers of episodic carbonate cementation during the Miocene Climatic Optimum in a paleolake of the Eger Rift","authors":"Daniel A. Petrash ,&nbsp;Patricia Roeser ,&nbsp;Bohdan Kříbek ,&nbsp;Philip T. Staudigel ,&nbsp;Miguel Bernecker ,&nbsp;Ivana Jačková ,&nbsp;Bohuslava Čejková ,&nbsp;Y.V. Erban Kochergina ,&nbsp;Magdaléna Koubová ,&nbsp;Šárka Křížová ,&nbsp;Ilja Knésl ,&nbsp;František Laufek ,&nbsp;Michael Ernst Böttcher ,&nbsp;Giovanna Della Porta ,&nbsp;Jens Fiebig","doi":"10.1016/j.gca.2025.08.025","DOIUrl":"10.1016/j.gca.2025.08.025","url":null,"abstract":"<div><div>Lacustrine carbonates are sensitive records of climate-driven environmental changes, with carbonates in terrigenous lake successions capturing variations in hydrochemistry, paleoproductivity, and weathering interactions, all potentially influenced by fluctuating atmospheric carbon dioxide levels (pCO₂). This complexity underscores the need to explore how various interlinked drivers impact lacustrine carbonate formation and alteration during pivotal climatic periods like the Miocene Climatic Optimum (MCO). Here we investigated ferroan dolomite and siderite as episodic pore-space filling cements within decimeter-scale claystone horizons. The targeted horizons are interbedded with carbonaceous claystone in the Lower Miocene lacustrine succession of the Sokolov sub-basin, Eger Graben, Czech Republic. During the MCO, intensified weathering of shale, K-rich basalt, mafic and granitic bedrocks enriched the paleolake with base cations and soil-derived nutrients. Microbial Fe- and Mn-respiration linked to an active nitrogen cycle sustained elevated shallow burial pore-water alkalinity and pH, driving episodic (Ca, Mg)-Fe carbonate cementation. High dissolved inorganic carbon (DIC), derived from organic matter remineralization and magmatic CO₂ degassing in the continental rift setting, along with favorable (Mg²⁺ + Fe²⁺)/Ca²⁺ ratios, facilitated interstitial ferroan dolomite growth in central lake facies, while siderite dominated transitional littoral-to-palustrine environments. The δ¹³C signatures (median = 8.3 ‰, mean = 9.0 ‰, range = [+1.8, +18.5]‰) provide evidence for significant methanogenesis influencing dissolved inorganic carbon (DIC) in the pore water–sediment system. Additionally, the lowest δ¹³C values observed reflect the admixture of ¹²C-enriched DIC derived from magmatic CO₂ or modified by attendant dissimilatory iron reduction. Bulk δ¹⁵N values suggest important nitrogen losses across the paleolake, possibly via denitrification and ammonia volatilization. Based on its clumped isotopologue contents, dolomite cements stabilized in near isotopic equilibrium with diagenetic pore waters at relatively low temperatures, <em>T</em>(Δ₄₇, Δ₄₈) ≤ 58 °C. Rare earth element (REE) patterns and ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd indicate transport of groundwater evolved after interaction with Paleogene basalts and Paleozoic shale and granitic bedrocks, while Ce anomalies revel a redox-buffered environment favorable to diagenetic carbonate precipitation. These findings highlight complex interactions regulating pore-water carbonate equilibrium in rift lakes. Early Miocene pCO₂ fluctuations intensified silicate weathering in alkaline igneous rocks of the catchment areas, delivering dolomite–ankerite–siderite reactants (Fe³⁺, Mg²⁺, Ca²⁺) into ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 47-66"},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900949","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":"Petrographic insights into phosphate formation in L and LL ordinary chondrites","authors":"Valentine Megevand, Alexander N. Krot, Adrian J. Brearley, François Guyot, Sylvain Bernard, Elena Dobrică","doi":"10.1016/j.gca.2025.08.023","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.023","url":null,"abstract":"The origin and formation mechanisms of phosphate minerals in L and LL ordinary chondrites remain an open question. Here we report detailed quantitative data on the abundances, grain sizes and compositions of apatite and merrillite in L, LL and L/LL chondrites, covering a total analysed area of ∼2730 mm<ce:sup loc=\"post\">2</ce:sup>. Our results show that the abundances of phosphate minerals are slightly higher in L than in LL chondrites and reveal distinct petrographic differences between merrillite and apatite. Merrillite abundance is anti-correlated with Fe, Ni metal content and increases with petrologic type, as does grain size – indicating grain coarsening processes – supporting the formation of this mineral during thermal metamorphism. In contrast, apatite shows no clear trend in abundance or grain size with petrologic type. Although chlorine contents are similar between apatites from L and LL chondrites, the small dispersion of Cl concentration and its decrease with petrologic type in LL chondrites indicate that apatites in these chondrites undergo equilibration with increasing thermal metamorphism, a pattern not observed in L chondrites. Although the Cl contents in apatites are fairly homogeneous across the samples, scarce F-rich apatites have been observed in some meteorites, leading to significant variability in Cl#. However, due to low concentrations and analytical challenges, we argue that comparisons between different OC groups should primarily be based on Cl concentrations. Furthermore, apatite and merrillite have different grain size distributions in L chondrites, but similar ones in LL chondrites, where they also occur as close assemblages, suggesting a petrogenetic relationship between apatite and merrillite in LL chondrites, but not in L chondrites. Overall, the present study suggests that phosphates did not have exactly the same history in L and LL chondrites.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900806","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":"Refining the signature of thallium isotopes in low oxygen marine environments","authors":"Sean M. Newby ,&nbsp;Siqi Li ,&nbsp;Silke Severmann ,&nbsp;James McManus ,&nbsp;Florian Scholz ,&nbsp;Jeremy D. Owens","doi":"10.1016/j.gca.2025.08.020","DOIUrl":"10.1016/j.gca.2025.08.020","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Thallium (Tl) isotopic values (ε&lt;sup&gt;205&lt;/sup&gt;Tl) appear to track changes in marine manganese oxide deposition, with these isotope signatures having been utilized as a proxy for rapid oceanic seafloor (de-)oxygenation events. With a residence time longer than ocean mixing time and the ability to track the deposition of manganese oxides, ε&lt;sup&gt;205&lt;/sup&gt;Tl may effectively record the earliest global transitions in the extent of ocean oxygenation. However, some uncertainty remains for the minor Tl sinks in degree of fractionation from seawater values, if any, with the limited data currently available suggesting at least a 6 epsilon unit range in fractionation from seawater values in low oxygen environments. This study provides Tl data for sediment cores from a range of low-oxygen marine environments. With these data, we identify potential processes that impact the range of Tl isotope variations within the sediments, which are not all due to local Mn oxide cycling. Previous work indicates that euxinic (anoxic and sulfidic water column) conditions and early diagenetic pyrite formed under consistently anoxic sediments record seawater values with no (or not measurable) fractionation during absorption to pyrite. Our new data provide downcore confirmation. Meanwhile, only limited data from ‘suboxic’ environments (those with low oxygen but likely not permanently anoxic conditions) has been analyzed. Thus, isotopic data for suboxic systems is needed to refine the current mass balance. Several sites off the California, Mexico, and Peru coasts with a range of redox states from oxic to perennially anoxic were selected to allow for a comparison across a range of open ocean bottom water conditions. The locations with oxic sediments tend to document more positive values compared to seawater, as expected due to local manganese oxide incorporation. Sediments from more ‘suboxic’ (manganous to ferruginous) sites tend to have invariable downcore geochemical signatures that are between marine inputs (−2) and modern seawater (−6) values, indicating a mixing of ε&lt;sup&gt;205&lt;/sup&gt;Tl signatures from different authigenic phases; however, these are not primarily due to the incorporation of Mn oxides as the concentrations are low and uncorrelated. The anoxic sites record Tl isotope compositions near seawater values, confirming that early diagenetically formed pyrite (and precursor minerals) record seawater ε&lt;sup&gt;205&lt;/sup&gt;Tl signatures under permanent anoxia. Importantly, these permanently anoxic localities have minor Mn contents, which suggest no local Mn oxide Tl isotope signatures. Therefore, unlike the anoxic sediments, the ‘suboxic’ sediments have a Tl isotope value that is slightly offset from seawater without significant Mn oxide deposition, thus suggesting there could be a fractionation for this process. Our observations provide improved constraints on the Tl isotope system, especially on a poorly constrained aspect of the mass balance, which will be important fo","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 338-356"},"PeriodicalIF":5.0,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900809","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":"Bacterial necromass-derived organic matter triggers greenhouse gas production and priming effect in saline lake sediments","authors":"Jian Yang, Min Cai, Pingping Zhang, Mingxian Han, Hailong Liu, Haiyi Xiao, Jibin Han, Xiying Zhang, Hongchen Jiang","doi":"10.1016/j.gca.2025.08.030","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.030","url":null,"abstract":"Bacterial necromass-derived OM constitutes a globally significant yet understudied reservoir of organic carbon and nitrogen, whose degradation dynamics in climate-sensitive saline lakes remain unresolved. This study quantifies how bacterially derived organic matter (OM) regulates CO<ce:inf loc=\"post\">2</ce:inf> and N<ce:inf loc=\"post\">2</ce:inf>O production and priming effects (PE) across a natural salinity gradient (0.9–247.0 g L<ce:sup loc=\"post\">−1</ce:sup>) in 20 lake sediments. Through microcosm experiments with <ce:sup loc=\"post\">13</ce:sup>C/<ce:sup loc=\"post\">15</ce:sup>N-labelled <ce:italic>Sphingomonas</ce:italic> sp. necromass, we demonstrate that OM addition significantly enhances CO<ce:inf loc=\"post\">2</ce:inf> and N<ce:inf loc=\"post\">2</ce:inf>O production rates (up to 104.73 μg C g<ce:sup loc=\"post\">−1</ce:sup> day<ce:sup loc=\"post\">−1</ce:sup> and 1,806.17 ng N g<ce:sup loc=\"post\">−1</ce:sup> day<ce:sup loc=\"post\">−1</ce:sup>, respectively;<ce:hsp sp=\"0.25\"></ce:hsp>p &lt; 0.001), concurrent with increased abundances of 16S rRNA and functional genes (archaeal <ce:italic>amoA</ce:italic>, <ce:italic>nirK</ce:italic>, <ce:italic>nosZ</ce:italic> I). Positive priming effects (PE) dominates (−12.56 to 8.47 μg C-CO<ce:inf loc=\"post\">2</ce:inf> g<ce:sup loc=\"post\">−1</ce:sup> day<ce:sup loc=\"post\">−1</ce:sup>), driven by upregulated prokaryotic taxa (<ce:italic>Bacteroidetes</ce:italic>, <ce:italic>Firmicutes</ce:italic>, and <ce:italic>Proteobacteria</ce:italic>) that preferentially decompose plant-derived organic molecules (e.g., lignin- and tannin-like compounds. Archaeal ammonia oxidation and<ce:hsp sp=\"0.25\"></ce:hsp>nirK-denitrification fueled by labile OM substrates are identified as key N<ce:inf loc=\"post\">2</ce:inf>O production pathways, with salinity suppressing CO<ce:inf loc=\"post\">2</ce:inf> fluxes but not N<ce:inf loc=\"post\">2</ce:inf>O emissions. FT-ICR-MS reveals molecular shifts in dissolved OM (increased CHONS/condensed aromatics; decreased CHO/lignins) linked to microbial community restructuring. These findings establish bacterial necromass-derived OM as a critical regulator of carbon and nitrogen cycling in saline lakes, urging its integration into biogeochemical models under climate change scenarios.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"27 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900810","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":"Understanding the relationship between foraminiferal Mg/Ca and clumped isotope thermometers","authors":"Marion Peral ,&nbsp;Thibaut Caley ,&nbsp;Bruno Malaizé ,&nbsp;Thomas Extier ,&nbsp;Linda Rossignol ,&nbsp;Héloïse Barathieu ,&nbsp;Émilie Dassié ,&nbsp;Franck Bassinot ,&nbsp;Dominique Blamart ,&nbsp;Mathieu Daëron","doi":"10.1016/j.gca.2025.08.011","DOIUrl":"10.1016/j.gca.2025.08.011","url":null,"abstract":"<div><div>Reconstructions of past sea surface temperatures (SSTs) are essential for understanding long-term climate variability, yet different proxy methods can yield divergent results. In this study, we compare Mg/Ca-derived SSTs from <em>Globigerinoides ruber</em> sensu stricto and <em>Trilobatus sacculifer</em> with clumped isotope (Δ₄₇) SSTs measured on <em>G. ruber</em> s.s. from the same core, MD96-2048 (Indian Ocean), covering the last 1.25 million years (Ma). Using the same species and samples allows minimizing ecological and environmental biases. We find that Δ₄₇-derived SSTs are systematically colder than Mg/Ca-SSTs prior to 0.4 Ma, while both proxies agree well after this point. This offset is not explained by diagenetic alteration (as assessed via SEM), nor by corrections for seawater salinity, pH, or Mg/Ca composition. The Mg/Ca-SSTs from <em>T. sacculifer</em> are more consistent with Δ₄₇-SSTs in the older interval, but do not fully resolve the discrepancy. We found that the apparent Δ₄₇-based cooling before 0.4 Ma is not supported by seawater δ¹⁸O estimates or other climate indicators. Our results suggest that Δ₄₇-derived SSTs may be affected by an unknown bias in older intervals, although a combination of multiple factors explored in this study could also contribute to the observed offset.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 253-264"},"PeriodicalIF":5.0,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900628","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":"Late Cenozoic Hainan OIB-like basalts in SE Asia record the interaction between a deep mantle plume and stagnant slab","authors":"Ming Lei ,&nbsp;Katsuhiko Suzuki ,&nbsp;Minako Kurisu ,&nbsp;Teruhiko Kashiwabara ,&nbsp;Jifeng Xu ,&nbsp;Zhengfu Guo ,&nbsp;Jie Li ,&nbsp;Jianlin Chen","doi":"10.1016/j.gca.2025.08.016","DOIUrl":"10.1016/j.gca.2025.08.016","url":null,"abstract":"<div><div>Whether Late Cenozoic basalts in SE Asia record plume-slab interactions within the mantle transition zone (MTZ) remains unresolved. To investigate this, we report new data on He isotopes measured in olivine, together with whole-rock major and trace element compositions and Sr–Nd–Hf–Fe–Mo isotope ratios for the Hainan basalts. The Hainan basalts have high MgO and low SiO₂ contents and display trace-element signatures of ocean island basalts (OIBs), such as the enrichments in light rare earth elements and high-field-strength elements. Meanwhile, these basalts are characterized by the depleted Sr–Nd–Hf isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0.7031–0.7043; εNd = +3.3 to +5.5; εHf = +6.8 to +10.3) and yield mid-ocean ridge basalts (MORBs)-like ³He/⁴He ratios (7.0–9.2 Ra). The geochemical characteristics of Hainan basalts illuminate that their mantle source includes depleted and enriched components. Compared with MORBs derived from upper mantle peridotite, the Hainan basalts have higher fractionation-corrected δ⁵⁶Fe values (+0.07 ‰ to +0.17 ‰) and variable δ⁹⁸Mo values (−0.38 ‰ to −0.07 ‰), indicating their source lithology was a pyroxenite formed by the interaction between ambient peridotite and recycled carbonate-bearing oceanic crust. Integrating geophysical constraints, we attribute the depleted and enriched signatures in the mantle source of Hainan basalts to a peridotitic FOZO plume and Pacific carbonate-bearing oceanic crust entrained from the MTZ, respectively. During the Late Cenozoic, an ascending mantle plume from the deep mantle reached the MTZ and reacted with the stagnant Pacific oceanic slab to form pyroxenite. Given the variable thickness and presence of a stagnant slab in the MTZ, the deep mantle plume bifurcated, leading to the formation of secondary mantle plumes. The upwelling secondary mantle plumes from the MTZ transported newly formed mantle pyroxenite into the upper mantle, where pyroxenite underwent partial melting to form the Hainan basalts and other basaltic rocks in SE Asia. Therefore, our model of the interplay between a deep mantle plume and a stagnant slab within the MTZ might be applied to explain the formation of Late Cenozoic basalts in this region. We further propose that MORB-like ³He/⁴He values in basaltic rocks (e.g., Hainan basalts) cannot be simply used as a robust indicator to negate the possibility that they may be sourced from a deep mantle plume. Moreover, the integration of radiogenic (Sr–Nd–Hf) and stable (Fe–Mo) isotope data for basaltic rocks is a robust method to reveal the presence of pyroxenite in the mantle source of basalts and shed light on its genesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 295-308"},"PeriodicalIF":5.0,"publicationDate":"2025-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900630","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}