Geochimica et Cosmochimica Acta最新文献

{"title":"Biomarker 14C evidence for sources and recycling of pre-aged organic carbon in Arctic permafrost regions","authors":"Julie Lattaud ,&nbsp;Timothy I. Eglinton ,&nbsp;Negar Haghipour ,&nbsp;Marcus Schiedung ,&nbsp;Lisa Bröder","doi":"10.1016/j.gca.2025.02.010","DOIUrl":"10.1016/j.gca.2025.02.010","url":null,"abstract":"<div><div>Permafrost thaw has the potential to release ancient particulate and dissolved organic matter that had been stored for thousands of years. Previous studies have shown that dissolved organic matter from permafrost is very labile and can be used by heterotrophic microbes close to the thaw area. However, it is unknown if ancient particulate organic matter can also be utilized. This study aims to investigate whether arctic microbial communities (bacteria and Archaea) incorporate ancient organic matter potentially released from thawing permafrost into their biomass. We compare and contrast the radiocarbon signatures of microbial lipids and higher plant biomarkers (representing terrestrial organic matter) from five soil profiles and seven deltaic lake sediment cores from the Mackenzie River drainage basin, Arctic Canada. In the surface soils, modern to post-modern short-chain fatty acids (SCFA) ages indicate <em>in situ</em> microbial production, with differential rates of organic carbon (OC) cycling depending on soil moisture. In contrast, SCFA in deeper soils display millennial ages, which likely represent the microbial necromass preserved through mineral association. In deltaic lakes that are disconnected from the river, generally old SCFA suggests the uptake of pre-aged OC by bacteria. In perennially connected lakes, pre-aged SCFA could originate from <em>in situ</em> microbial uptake of old OC or from the Mackenzie River. Higher plant-derived long-chain fatty acids (LCFA) present older radiocarbon ages, reflecting mineral stabilization during either pre-aging in soils (for high closure lakes) or riverine transport (for no and low closure lakes). Archaeal lipids are younger than SCFA and LCFA in high closure lakes, and older in low and no closure lakes, mirroring bulk radiocarbon signatures due to their heterotrophic production. These radiocarbon signatures of bacterial biomarker lipids may therefore reflect microbial incorporation of ancient OC (e.g., derived from permafrost thaw) or exceptional preservation (e.g., through mineral stabilization). Hence, even in relatively high OC environments such as arctic aquatic ecosystems, microbes can rely on ancient OC for their growth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 75-85"},"PeriodicalIF":4.5,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395210","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":"Effect of temperature on 2H/1H fractionation in semi-continuous cultures of a marine diatom, coccolithophore, and dinoflagellate","authors":"Jiawei Gao ,&nbsp;Rong Bi ,&nbsp;Julian P. Sachs ,&nbsp;Hailong Zhang ,&nbsp;Yunning Cao ,&nbsp;Matthew D. Wolhowe ,&nbsp;Weiguo Liu ,&nbsp;Meixun Zhao","doi":"10.1016/j.gca.2025.02.005","DOIUrl":"10.1016/j.gca.2025.02.005","url":null,"abstract":"<div><div>Temperature regulates the metabolic rate of organisms and, together with salinity, determines seawater density, a key driver of ocean circulation and heat transport. The hydrogen isotope composition (²H/¹H) of phytoplankton lipids has been shown to vary systematically with salinity and applied as a paleosalinity proxy in marine sediments. The influence of temperature on ²H/¹H ratios of lipids from different phytoplankton groups remains poorly constrained, especially when other growth parameters known to influence ²H/¹H fractionation are held constant, such as growth rate, irradiance, and salinity. We investigated ²H/¹H ratios responses of lipid biomarkers (fatty acids (FAs), sterols and alkenones) to temperature (12 ∼ 27 °C) in three marine phytoplankton taxa, the diatom <em>Phaeodactylum tricornutum</em>, the dinoflagellate <em>Prorocentrum donghaiense</em>, and the coccolithophorid <em>Emiliania huxleyi</em> using semi-continuous cultures. We show that ²H/¹H fractionation of FAs in the dinoflagellate decreased by 2.2 ± 0.3 ‰ °C^–1 (<em>p</em> &lt; 0.05), while that of sterols in the dinoflagellate and fatty acid C_14:0 in the diatom increased by 2.3 ‰ °C^–1 and 1.9 ‰ °C^–1 (<em>p</em> &lt; 0.05), respectively, as temperature increased. ²H/¹H fractionation of the three types of lipids in the coccolithophores did not vary systematically with temperature. The underlying mechanism by which temperature alters lipid ²H/¹H fractionation likely involves its effect on the proportions of photosynthetic and metabolic NADPH incorporated into lipids, NADPH residence time in the chloroplast, the contribution of extra-plastidic pyruvate to FA synthesis, and the proportion of mevalonic acid- versus methylerythritol phosphate-derived precursors in sterols.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 86-97"},"PeriodicalIF":4.5,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395209","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":"Moderately volatile elements in chondrites record chondrule formation, two-component mixing and redistribution on parent bodies","authors":"Ninja Braukmüller ,&nbsp;Claudia Funk ,&nbsp;Wafa Abouchami ,&nbsp;Harvey Pickard ,&nbsp;Mark Rehkämper ,&nbsp;Alessandro Bragagni ,&nbsp;Stephen J.G. Galer ,&nbsp;Carsten Münker ,&nbsp;Harry Becker ,&nbsp;Frank Wombacher","doi":"10.1016/j.gca.2025.02.001","DOIUrl":"10.1016/j.gca.2025.02.001","url":null,"abstract":"<div><div>Most chondrites are depleted in moderately volatile elements (MVE) relative to the bulk solar system composition represented by CI chondrites. Here we present high-precision isotope dilution data for 11 moderately volatile elements (S, Cu, Zn, Ga, Se, Ag, Cd, In, Sn, Te and Tl) together with Cd and Zn stable isotope compositions for carbonaceous, ordinary, enstatite and Rumuruti chondrites complemented by a literature compilation of MVE stable isotope compositions. Together these data allow new insights into the processes that led to MVE depletion in chondrites and their redistribution within parent bodies.</div><div>Moderately volatile element abundances in carbonaceous, ordinary and Rumuruti chondrites are best explained by two-component mixing between a chemically CI-like MVE-rich matrix and an MVE-poor refractory component dominated by chondrules. Chondrules are enriched in light MVE isotopes due to kinetic recondensation of a small vapor fraction initially lost from chondrules upon heating. Later, thermal metamorphism redistributed some MVE within chondrite parent bodies, which is evaluated here in a systematic way for different chondrite groups and plateau volatile elements based on related and comparatively large but unsystematic stable isotope fractionation. Compared to other chondrite classes, enstatite chondrites show less systematic MVE abundance patterns when the elements are plotted as a function of condensation temperatures. Type 3 and 4 enstatite chondrites are more MVE-rich than expected based on their low matrix fractions and are enriched in light Zn and Te isotopes relative to CI. The enrichment of light Zn and Te isotopes and high MVE abundances in type 3 and 4 enstatite chondrites relative to CI can be explained by recondensation of a larger MVE vapor fraction after chondrule formation than observed for other chondrite classes, which presumably occurred at comparatively high H₂ pressures. Because MVE abundances and isotope compositions are fully consistent with chondrule formation, two-component mixing and MVE redistribution on parent bodies, we refute partial condensation from a hot solar nebula as the cause for MVE depletion in chondrite formation regions of the protoplanetary disk.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 43-62"},"PeriodicalIF":4.5,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143379268","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":"Sources and fate of particulate organic matter along the river-estuary-coastal ocean continuum: Constraints from amino acid and amino sugar carbon isotopes","authors":"Jinqiang Guo ,&nbsp;Eric P. Achterberg ,&nbsp;Yuan Shen ,&nbsp;Bu Zhou ,&nbsp;Jinming Song ,&nbsp;Xuegang Li ,&nbsp;Liqin Duan ,&nbsp;Huamao Yuan","doi":"10.1016/j.gca.2025.02.004","DOIUrl":"10.1016/j.gca.2025.02.004","url":null,"abstract":"<div><div>Estuaries represent hotspots for organic matter cycling. Understanding the sources and fate of organic matter in estuaries is crucial for quantifying the transport of terrestrial organic carbon to the coastal ocean and air-sea carbon dioxide fluxes. Here we report the abundance and carbon isotopic signatures of bulk particulate organic matter (POM) as well as particulate amino sugars and amino acids in surface suspended particles along the salinity gradient in the Changjiang Estuary and adjacent coastal ocean. Our data show that bulk δ¹³C values are directly related to the δ¹³C values of essential amino acids, suggesting a control by primary production on bulk δ¹³C values. A large degree of fractionation (−26‰) between phytoplankton δ¹³C and dissolved inorganic carbon δ¹³C values was observed in regions with salinities greater than 28, leading to a decline in bulk δ¹³C values. Examining the δ¹³C patterns of individual amino sugars and amino acids reveals that terrestrial amino sugars are produced by mixed sources of bacteria, fungi, and algae, while terrestrial amino acids originate from vascular plants and bacteria. Along the salinity gradient, the source of amino sugars shifted to bacteria, whereas amino acids transitioned to algae. Moreover, the low carbon- and nitrogen-normalized yields of amino acids (∼10% and ∼22%, respectively) observed in the Changjiang River suggest an advanced diagenetic state of terrestrial POM. In contrast, elevated POM reactivity in moderate to high salinity zones indicates contributions from phytoplankton production. Using the bacterial biomarker muramic acid, we found that a substantial portion (∼19%) of terrestrial POM is of bacterial origin. Combining the distinct excursions in bulk, amino sugar, and amino acid δ¹³C values in low salinity (&lt;20) regions of the estuary indicates that terrestrial organic matter is extensively removed in the estuarine regions. Together, these findings underscore significant alterations in the sources and properties of organic matter along the river-estuary-coastal ocean continuum, with bacterial reworking playing an important role.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 31-42"},"PeriodicalIF":4.5,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377826","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":"Soda lake phosphorus fluxes controlled by biological uptake imply abundant phosphate in plausible origin-of-life environments","authors":"Sebastian Haas ,&nbsp;Benjamin M. Tutolo ,&nbsp;David C. Catling","doi":"10.1016/j.gca.2025.01.040","DOIUrl":"10.1016/j.gca.2025.01.040","url":null,"abstract":"<div><div>Phosphate is crucial for the origin of life but typical environmental concentrations are too low for prebiotic synthesis of essential biomolecules like nucleic acids. However, evaporative, sodium-carbonate rich “soda” lakes can accumulate extreme phosphate levels sufficient for prebiotic synthesis. In modern soda lakes, this presumably requires small biological and inorganic (apatite mineral formation) sinks, but the relative importance of these sinks is unclear because studies on phosphorus fluxes in soda lakes are lacking. Here, we quantified phosphorus source and sink fluxes in the extremely phosphate-rich Last Chance Lake (LCL), Canada, and neighboring, moderately phosphate-rich, Goodenough Lake (GL). Within the total phosphorus (0.1 wt%) in LCL sediments, sequential extraction showed 61 % detrital apatite, ∼19 % dissolved phosphate, ∼11 % organic-bound phosphorus (P_org), 6 % carbonate-bound P, and ∼2 % authigenic apatite. Combining these measurements with hydrological fluxes, we demonstrate that evapo-concentration of dilute inflow sufficed to accumulate tens of millimolar phosphate on a millennial timescale due to small sinks. Low apatite formation rates directly confirmed a previously hypothesized mechanism allowing extreme phosphate solubility at high carbonate concentrations. Yet, it is its 18 × lower P_org formation rates that mainly distinguish LCL from the less phosphate-rich, more biologically active GL. Because low productivity is key, evaporative soda lakes on prebiotic Earth should have commonly attained millimolar phosphate levels. Consequently, we identify soda lakes as the only known natural environments with sufficiently high phosphate levels for critical phosphorylation and catalysis in prebiotic synthesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 63-74"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143388324","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":"Temperature dominates leaf wax n-alkane carbon isotope composition of terrestrial C3 angiosperms in humid zones","authors":"Yuhang Wang, Zhengshun Liu, Mingming Zhang, Gaowen Dai, Xianyu Huang","doi":"10.1016/j.gca.2025.01.045","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.045","url":null,"abstract":"The C<ce:inf loc=\"post\">3</ce:inf> plant leaf wax δ<ce:sup loc=\"post\">13</ce:sup>C (δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf>) is commonly used to reconstruct past climates. However, our understanding of how precipitation and temperature influence terrestrial C<ce:inf loc=\"post\">3</ce:inf> δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf> is limited. To address this gap, we investigated the δ<ce:sup loc=\"post\">13</ce:sup>C of <ce:italic>n</ce:italic>-C<ce:inf loc=\"post\">29</ce:inf> alkane (δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf>) of C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms in subtropical humid regions in China and compiled a global dataset. Results show a strong correlation between C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf> and mean annual temperature in both Chinese subtropical humid regions (r = −0.94, <ce:italic>p</ce:italic> &lt; 0.001) and global humid zones (r = −0.78, <ce:italic>p</ce:italic> &lt; 0.001). The linear fit lines of the regional and global datasets have similar slopes (−0.3129 vs −0.2896) and intercepts (−30.82 vs −31.41), indicating consistent responses to air temperature in global humid zones. When considering only sites with temperature data from meteorological stations, the correlation coefficient increases to −0.96 (<ce:italic>p</ce:italic> &lt; 0.001) for the global dataset. In contrast to humid zones, mean annual precipitation significantly correlates with C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf> in arid zones (r = −0.75, <ce:italic>p</ce:italic> &lt; 0.001), supporting the main controls of precipitation in these areas. These findings emphasize the impact of temperature on C<ce:inf loc=\"post\">3</ce:inf> terrestrial δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf>, particularly in humid zones, and highlight caution when interpreting δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf> in geological records under changing hydroclimate conditions or unstable settings.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"10 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401583","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":"Monazite saturation in carbonatite melts at crustal and upper mantle conditions","authors":"Srijita Ray ,&nbsp;Gregory M. Yaxley ,&nbsp;Laura A. Miller ,&nbsp;Andrew J. Berry","doi":"10.1016/j.gca.2025.01.039","DOIUrl":"10.1016/j.gca.2025.01.039","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Monazite (XPO&lt;sub&gt;4&lt;/sub&gt; where X  = light rare earth element) is one of the most important ore minerals for rare earth elements (REE) mined from carbonatites. This study explores the influence of pressure, temperature and melt composition on the solubility of monazite in carbonate melt using piston cylinder experiments. We aim to understand how such a highly soluble phosphate mineral may sometimes crystallise from carbonatite magma and form economic deposits of REE. Our findings reveal that the solubility of monazite in a sodic-dolomitic carbonate melt is high over the entire pressure (1.0–2.0 GPa), temperature (1000-1450˚C), and compositional space (Na&lt;sub&gt;2&lt;/sub&gt;O-CaO-MgO-SiO&lt;sub&gt;2&lt;/sub&gt;-F) of our study. It increases from ∼ 26 to ∼ 61 wt% CePO&lt;sub&gt;4&lt;/sub&gt; equivalent over the temperature range of 1000–1450 °C at 2 GPa. However, the solubility product constant (lnK&lt;sub&gt;sp&lt;/sub&gt;) decreases by approximately ∼ 23 % and 21 % equivalent with increasing melt SiO&lt;sub&gt;2&lt;/sub&gt; (from 0 to ∼ 18 wt% melt SiO&lt;sub&gt;2&lt;/sub&gt;) at 1275 °C and fluoride (from 0 to ∼ 5 wt% melt F&lt;sup&gt;-&lt;/sup&gt;) concentrations at 1100 °C respectively. Variations in melt Ca# (atomic Ca/(Mg + Ca) = 0.2–1.0) and pressure (1.0–2.0 GPa) have negligible impacts on monazite solubility. We use the experimental data to formulate an empirical model relating the solubility product constant (K&lt;sub&gt;sp&lt;/sub&gt;) of monazite in carbonate melt to temperature and melt compositional parameters:&lt;/div&gt;&lt;div&gt;&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;lnK&lt;/mi&gt;&lt;mi&gt;sp&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;ln&lt;/mi&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mfenced&gt;&lt;msub&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;E&lt;/mi&gt;&lt;mi&gt;E&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;l&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mfenced&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mfenced&gt;&lt;msub&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;5&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;l&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;1.31&lt;/mn&gt;&lt;mfenced&gt;&lt;mn&gt;0.50&lt;/mn&gt;&lt;/mfenced&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mn&gt;8679&lt;/mn&gt;&lt;mfenced&gt;&lt;mn&gt;733&lt;/mn&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;/mfrac&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;3.35&lt;/mn&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;0.34&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mfenced&gt;&lt;msub&gt;&lt;mi&gt;SiO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mfenced&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;mn&gt;1.68&lt;/mn&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;0.34&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mfenced&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;/mfenced&gt;&lt;/math&gt;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;where [] represents the mole fractions of oxides in the melt of the rare earth elements, phosphorus and silicon, and fluoride, T is in Kelvin, and the parentheses indicate standard errors. &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;E&lt;/mi&gt;&lt;mi&gt;E&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;m&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;l&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; represents the summation of the melt REE concentrations for those REE which are compatible in the experimentally synthesized monazite (La-Sm and Gd). These experimental results suggest that the formation of monazite requires relatively high co","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377824","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":"Competitive incorporation of Ca, Sr, and Ba ions into amorphous carbonates","authors":"Zsombor Molnár ,&nbsp;Máté Hegedűs ,&nbsp;Péter Németh ,&nbsp;Mihály Pósfai","doi":"10.1016/j.gca.2025.02.002","DOIUrl":"10.1016/j.gca.2025.02.002","url":null,"abstract":"<div><div>Amorphous alkaline earth carbonates typically occur as metastable precursors of widespread crystalline phases. Despite their transient nature, the properties of the amorphous carbonates affect the attributes of the crystalline end-products. The lack of long-range ordering in the amorphous solids allows for the incorporation of various ions into their structures, resulting in a wider range of cation compositions than in crystalline carbonate phases, furnishing these solids with peculiar physico-chemical properties. Here, we studied abiotic factors that could control the degree of incorporation of Ca²⁺, Sr²⁺, and Ba²⁺ cations into amorphous carbonates, and focused on the effects that different cation compositions have on the lifetimes and structures of amorphous solids, as well as on the structures of their crystalline end-products. The partition coefficients (D_Ca, D_Sr, and D_Ba) between the solution and the solid decreased with increasing ionic radius; however, in ternary systems the incorporation of Ba²⁺ was favored over Sr²⁺. Electron diffraction patterns and pair distribution functions calculated from them showed that incorporated Sr²⁺ and Ba²⁺ cations significantly modified the structural properties of the amorphous carbonates (relative to amorphous calcium carbonate). The changes in short-range structure resulted in exceptional kinetic stability of the ternary mixed amorphous Ca–Sr–Ba carbonates, with the lifetime of Sr₀_.1Ba_.40Ca_.50C 65 times longer than that of amorphous calcium carbonate. Ba²⁺ enhanced the formation of calcite-type structures, even in the presence of Sr²⁺. These findings contribute to the understanding of both the incorporation of alkaline earth metals into amorphous carbonates and their roles in prolonging the lifetimes of amorphous solids; in addition, our results can be potentially used for technological applications.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 18-30"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377825","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":"Potassium isotopic compositions and model exposure ages of lunar soils","authors":"Kun Wang, Zhen Tian, Megan Broussard, Mason Neuman, Piers Koefoed, Olga Pravdivtseva, Guillaume Avice, Richard V. Morris, Kees C. Welten, Randy L. Korotev, Bradley L. Jolliff","doi":"10.1016/j.gca.2025.01.043","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.043","url":null,"abstract":"Space weathering has long been known to alter the chemical and physical properties of the surfaces of airless bodies such as the Moon. The isotopic compositions of moderately volatile elements in lunar regolith samples could serve as sensitive tracers for assessing the intensity and duration of space weathering. In this study, we develop a new quantitative tool to study space weathering and constrain surface exposure ages based on potassium isotopic compositions of lunar soils. We first report the K isotopic compositions of 13 bulk lunar soils and 20 interval soil samples from the Apollo 15 deep drill core (15004 – 15006). We observe significant K isotope fractionation in these lunar soil samples, ranging from 0.00 ‰ to + 11.77 ‰, compared to the bulk silicate Moon (–0.07 ± 0.09 ‰). Additionally, a strong correlation between soil maturity (<ce:italic>I<ce:inf loc=\"post\">s</ce:inf></ce:italic>/FeO) and K isotope fractionation is identified for the first time, consistent with other isotope systems of moderately volatile elements such as S, Cu, Zn, Se, Rb, and Cd. Subsequently, we conduct numerical modeling to better constrain the processes of volatile element depletion and isotope fractionation on the Moon and calculate a new K Isotope Model Exposure Age (KIMEA) through this model. We demonstrate that this KIMEA is most sensitive to samples with an exposure age lower than 1,000 Ma and becomes less effective for older samples. This novel K isotope tool can be utilized to evaluate the surface exposure ages of regolith samples on the Moon and potentially on other airless bodies if calibrated using other methods (e.g., cosmogenic noble gases) or experimental data.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controls on the distribution of dissolved Cr in the upper water column of the Atlantic Basin","authors":"D. Gilliard ,&nbsp;D.J. Janssen ,&nbsp;N. Schuback ,&nbsp;S.L. Jaccard","doi":"10.1016/j.gca.2024.10.017","DOIUrl":"10.1016/j.gca.2024.10.017","url":null,"abstract":"<div><div>Over the last decades, the chromium (Cr) stable isotope system (referred to as δ⁵³Cr) has emerged as a proxy to reconstruct past oxygenation changes in Earth’s atmosphere and oceans. Although Cr is a promising paleoproxy, uncertainties remain as to the modern marine Cr cycle, and limited data are yet available in large swaths of the ocean, including the Atlantic Ocean. Here we present dissolved seawater Cr concentrations ([Cr]) and δ⁵³Cr along a meridional transect from the North to the South Atlantic (AMT 29). Chromium concentrations range from of 2.51 to 3.96 nmol kg⁻¹ (n = 68) and δ⁵³Cr values range from +0.86 ± 0.04 ‰ (2SEM) to +1.20 ± 0.02 ‰ (2SEM) (n = 68). In contrast to data from other ocean basins [Cr] and δ⁵³Cr show only a weak correlation (δ⁵³Cr vs. Ln([Cr]) R² = 0.17), inconsistent with a closed-system Rayleigh distillation model. These results can mainly be explained by horizontal advection and water mass mixing, which our data demonstrate are the dominant processes controlling [Cr] and δ⁵³Cr distributions throughout much of the Atlantic, while the impact of in situ biogeochemical cycling is comparatively minor. There is, indeed no clear impact of biological productivity nor of dysoxic environments in the (sub)tropical Atlantic on the cycling of Cr along the transect. This is likely explained by insufficiently depleted oxygen concentrations and relatively low biological productivity, resulting in these processes being of secondary importance relative to water mass mixing in shaping the distribution of Cr in the low- to mid-latitude Atlantic Ocean.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 57-69"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673652","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}