Geochimica et Cosmochimica Acta最新文献

{"title":"Dissolved zinc and cadmium isotope systematics in the Amundsen and Weddell coastal Antarctic marginal seas","authors":"Hung-An Tian ,&nbsp;Mathijs van Manen ,&nbsp;Charlotte Eich ,&nbsp;Jinyoung Jung ,&nbsp;Willem H.v.d. Poll ,&nbsp;Gert-Jan Reichart ,&nbsp;Tim M. Conway ,&nbsp;Rob Middag","doi":"10.1016/j.gca.2025.04.017","DOIUrl":"10.1016/j.gca.2025.04.017","url":null,"abstract":"<div><div>Coastal Antarctica is experiencing rapid environmental change with potential effects on regional marine trace element biogeochemistry. Here, we investigate the biogeochemistry of two dissolved bioactive trace elements, zinc (Zn) and cadmium (Cd), and their isotope ratios (δ⁶⁶Zn and δ¹¹⁴Cd) in two coastal marginal seas with distinct oceanographic features – the Amundsen Sea with the intrusion of Circumpolar Deep Water (CDW) onto the Antarctic continental shelf, and the Weddell Sea where formation of Antarctic Bottom Water occurs. In the Amundsen Sea, our isotope data show CDW predominantly controls δ⁶⁶Zn and δ¹¹⁴Cd on the continental shelf. This result is consistent with previous concentration-focused studies that suggested only a negligible addition of Zn and Cd from continental sediments and ice shelf meltwater, and other processes (e.g., scavenging) play a limited role in their cycling on the shelf region. In the Weddell Sea, homogeneous δ⁶⁶Zn and δ¹¹⁴Cd within different water masses across the Antarctic Peninsula shelf, while Zn and Cd concentrations increase via physical mixing with deep water masses, suggest a preformed isotope signature on the continental shelf. In surface waters of both regions, δ¹¹⁴Cd exhibited isotope fractionation linked to biological uptake, with different Rayleigh closed system fractionation factors (α = R_biomass/R_seawater) for regions dominated by haptophytes (0.99930–0.99960) and diatoms (0.99970–0.99995) and we speculate that such differences may be associated with variability between species. In contrast, estimated fractionation factors for Zn in haptophytes (0.99995) and diatoms (0.99980–0.99995) dominated blooms are similar and comparable to reported values in the Southern Ocean (0.99995 ± 0.00001). At the intermediate depth (250–1500 m) in the Weddell Sea, significantly lower δ¹¹⁴Cd in the inner gyre compared to the outer gyre implies Cd regeneration and reduced ventilation. This pattern was not observed for δ⁶⁶Zn, likely due to its smaller biological fractionation in the surface. These findings confirm the role of CDW as the main source of Zn and Cd to the Amundsen Sea and the importance of physical mixing in setting global dissolved Zn and Cd distributions during the formation of deep waters in the Weddell Sea, providing insights into the impacts of regional coastal systems on the biogeochemistry of Zn and Cd.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 93-110"},"PeriodicalIF":4.5,"publicationDate":"2025-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083385","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":"A phytol εp-based core-top calibration to reconstruct past changes in atmospheric CO2","authors":"Olivia A. Graham ,&nbsp;Caitlyn R. Witkowski ,&nbsp;Mark A. Stevenson ,&nbsp;Francien Peterse ,&nbsp;B. David A. Naafs","doi":"10.1016/j.gca.2025.04.014","DOIUrl":"10.1016/j.gca.2025.04.014","url":null,"abstract":"<div><div>Proxy-based reconstructions of past changes in atmospheric carbon dioxide concentrations (<em>p</em>CO₂) are essential for understanding climate dynamics. A common method for reconstructing past <em>p</em>CO₂ is based on the carbon isotopic fractionation during photosynthesis by Rubisco (ε_p). This proxy method is based upon the difference (ε_p) between the stable carbon isotopic composition (δ¹³C) of dissolved CO₂ and the δ¹³C of marine photoautotroph biomass, which depends on the concentration of dissolved CO₂, related to <em>p</em>CO₂ through Henry’s Law. This method has been applied to the general phytoplankton biomarker chlorophyll (preserved as isoprenoids like phytol, phytane, and pristane in the sedimentary record) to reconstruct photoautotroph biomass δ¹³C. The long-term stability of these chlorophyll-derived biomarkers in the sedimentary record has currently allowed the reconstruction of <em>p</em>CO₂ across the Phanerozoic (∼450 million years). However, the chlorophyll-derived biomarker proxy currently lacks a robust validation within modern settings. Here we investigate the relationship between the δ¹³C of chlorophyll (as phytol) and the concentration of dissolved CO₂ in the modern ocean using a globally distributed set of 30 marine core top sediments and 75 suspended particulate matter samples. Our results demonstrate a positive relationship between the extent of fractionation (higher phytol ε_p) and dissolved CO₂ concentration. This marks the first empirical calibration between phytol ε_p and the concentration of dissolved CO₂ in natural settings. We find that terrestrial input negatively affects this observed relationship, and the exclusion of coastal samples from our dataset improves the correlation. When applied to previously published Pleistocene proxy data, our new calibration provides an improved <em>p</em>CO₂ reconstruction with estimates that are statistically like direct <em>p</em>CO₂ measurements from the Antarctic ice cores. When applied to published data from the entire Phanerozoic, our calibration provides estimates in line with those of other proxy methods, emphasizing the potential of chlorophyll for reconstructions of <em>p</em>CO₂ across geological time.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 178-192"},"PeriodicalIF":4.5,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901829","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":"Hydrogen and triple-oxygen isotope effects of water adsorption on KGa-2 kaolinite with implications for pedological separation of soil water","authors":"Juske Horita, Xinying Ling, Changjie Liu, Osamu Abe, Ryu Uemura","doi":"10.1016/j.gca.2025.04.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.013","url":null,"abstract":"A series of detailed, systematic experiments were conducted to determine hydrogen and triple-oxygen isotope effects of water adsorption on KGa-2 kaolinite from the Clay Mineral Society at 30 °C as a function of the relative vapor pressure (<ce:italic>p/p<ce:inf loc=\"post\">o</ce:inf></ce:italic>). Both hydrogen and oxygen isotope fractionation factors between the adsorbed water and water vapor are smaller than those of the liquid water – water vapor (L-V) system even near the saturation. They gradually decrease with decreasing <ce:italic>p/p<ce:inf loc=\"post\">o</ce:inf></ce:italic>, approaching the isotopic property of water vapor. The ratio of hydrogen to oxygen fractionation factors increases from that of the L-V system (8.0) with decreasing <ce:italic>p/p<ce:inf loc=\"post\">o</ce:inf></ce:italic>. The exponent <ce:sup loc=\"post\">17</ce:sup><ce:italic>θ</ce:italic> for the triple oxygen isotope system also deviates from that of L-V (0.529) up to 0.585 well above the high-temperature limit (0.5305). Our experimental results clearly demonstrate that the isotopic property of water confined in pores and adsorbed on the mineral surface differs significantly from that of bulk liquid water with wide-ranging implications for stable isotope tracers of soil waters in the terrestrial and extraterrestrial hydrological systems, including a new concept of the ‘pedological separation.’","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"42 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901852","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":"Molybdenum isotopes record dehydrated slab components input to arc magmatism in subduction zones","authors":"Jin-Lei Sun ,&nbsp;Zhong-Jie Bai ,&nbsp;Wei-Guang Zhu ,&nbsp;Xu Liu","doi":"10.1016/j.gca.2025.04.011","DOIUrl":"10.1016/j.gca.2025.04.011","url":null,"abstract":"<div><div>The traditional model that attributes the genesis of basaltic arc magma to the partial melting of metasomatized mantle wedges is increasingly being challenged by evidence highlighting the critical role of dehydrated oceanic crust. Molybdenum (Mo) isotopes (expressed as <em>δ</em>^98/95Mo, relative to the NIST SRM 3134 standard) from subarc mantle-derived mafic cumulate rocks offer a novel perspective on this issue. This study reports <em>δ</em>^98/95Mo values with whole-rock Sr-Nd isotopes for the Late Cretaceous Milin juvenile lower crustal mafic–ultramafic cumulates in the Gangdese belt, Tibet. The Milin samples exhibit low initial (⁸⁷Sr/⁸⁶Sr)_i ratios ranging from 0.70392 to 0.70454 and depleted εNd(t) values between 3.26 and 4.45. These samples display a significant variation in <em>δ</em>^98/95Mo values (–0.64 to –0.05 ‰), with a lower mean value of –0.38 ‰ compared to depleted mantle values (–0.21 ± 0.02 ‰). The light Mo isotopes show no correlations with MgO content, Sr-Nd isotopes, or whole-rock hornblende content, suggesting that observed light Mo isotopes are associated with dehydrated oceanic crust rather than crustal processes (crustal contamination or fractional crystallization). The positive correlation between Ba/Th and Ba/La ratios and <em>δ</em>^98/95Mo values indicates the overprinting of subduction fluids. According to the Mo-Sr-Nd isotopic mixing model, the Milin mantle source incorporated minor subduction fluids (∼1 %), reduced sediment melts (∼1 %) and less than 30 % dehydrated oceanic crust melts, which leads to its heterogeneity and significant variation in the light Mo isotopes within the Milin lower crustal mafic–ultramafic cumulates. We suggest that such lower crust with oceanic crust melts in their source can serve as an important light Mo isotopic reservoir. Integrating the Mo isotopic features in global subduction zones, we propose that the thermal structure of the subduction zones controls the input of dehydrated oceanic crust melts into basaltic arc magmas, resulting in the predominant participation of oceanic crust in the basaltic arc magma genesis within the hot arc and back-arc regions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 152-162"},"PeriodicalIF":4.5,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901854","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":"A reconstruction of the H2O and F contents of the Erg Cech 002 parent body","authors":"Liam D. Peterson ,&nbsp;Megan E. Newcombe ,&nbsp;Conel M.O’D. Alexander ,&nbsp;Jianhua Wang ,&nbsp;Sune G. Nielsen","doi":"10.1016/j.gca.2025.04.009","DOIUrl":"10.1016/j.gca.2025.04.009","url":null,"abstract":"<div><div>Erg Cech 002 (EC 002) is an andesitic achondrite, the earliest formed achondrite identified to date, and is a rare sample of primary melts that formed crusts on the first generation(s) of planetesimals. Given that EC 002 represents a primary or primitive melt and that H and F are incompatible during silicate partial melting, EC 002 may be a H- and F-rich material relative to previously studied achondrites. We measured the H₂O (total H quantified as H₂O) and F contents of low-Ca pyroxene xenocrysts (∼4–12 µg/g H₂O; &lt;0.5 µg/g F), groundmass augite (∼5–10 µg/g H₂O; &lt;2.2 µg/g F), albitic feldspar (∼2–5 µg/g H₂O; &lt;0.5 µg/g F), and a silica-rich phase (∼28–30 µg/g H₂O; ∼0.7–2.5 µg/g F) in EC 002 by Nanoscale Secondary Ion Mass Spectrometry. We use a single-stage equilibrium batch melting model to provide a first-order reconstruction of the EC 002 parent body H₂O (∼7–200 µg/g H₂O) and F (∼0.44–2.4 µg/g F) contents, which are depleted relative to chondrites and the bulk Earth. This requires the first generation(s) of planetesimals to have either accreted from volatile-poor materials or undergone extensive volatile loss, supporting the idea that Earth acquired its H₂O budget from thermally primitive materials.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 82-92"},"PeriodicalIF":4.5,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901853","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":"Hydrogen and Oxygen Stable Isotope Compositions of Kaolinite Hydroxyl Water and their Paleoenvironmental Significance","authors":"Erik J.H. Oerter","doi":"10.1016/j.gca.2025.04.006","DOIUrl":"10.1016/j.gca.2025.04.006","url":null,"abstract":"<div><div>The phyllosilicate clay mineral kaolinite can preserve paleoclimate information on the hydrogen and oxygen stable isotope composition of the water the mineral formed from, as well as its formation temperature. Oxygen in kaolinite exists in three distinct bonded groups: Si-O-Si, Si-O-Al, and Al-OH; and it has been an outstanding analytical problem to feasibly and accurately measure the oxygen isotope compositions of the different groups. The ability to make δ¹⁸O_Al-OH measurements on kaolinite using thermogravimetry-enabled isotope ratio infrared spectroscopy (TGA-IRIS) is established herein. Using complementary fluorination and IRMS measurements, we add to the limited knowledge of intracrystalline oxygen isotope fractionation between that bound into Al-OH^- groups in kaolinite, and that of the bulk mineral, of which the average value is 1000 ln<span><math><mrow><msubsup><mo>∝</mo><mrow><mi>Total</mi><mo>-</mo><mi>O</mi><mi>H</mi></mrow><mi>O</mi></msubsup><mspace></mspace></mrow></math></span> = 18.9 ‰. Together with δ²H_Al-OH measurements on kaolinite, we demonstrate the extent to which hydrogen in the Eocene-age paleo-Oxisol Ione Fm has isotopically exchanged with water after its initial formation. At Mesa Alta, New Mexico, kaolinite hydrogen appears to be pristine since its initial formation 147 Ma BP (early Cretaceous), and we use δ²H_Al-OH, δ¹⁸O_Al-OH, and δ¹⁸O_Total measurements to determine a paleo-environmental temperature of 26.9 °C, which is significantly warmer than the modern MAT of 8.9 °C. These examples illustrate the utility of TGA-IRIS to yield paleoclimatic information on the globally ubiquitous kaolinite mineral.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 1-10"},"PeriodicalIF":4.5,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143850618","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":"Chromium isotope fractionation during magmatic processes of island arc basalts","authors":"Li-Juan Xu, Chunyang Liu, Haibo Ma, Qianru Man, Ji Shen, Sheng-Ao Liu, Guochun Zhao, Gerhard Wörner","doi":"10.1016/j.gca.2025.04.008","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.008","url":null,"abstract":"We present the first stable chromium isotope dataset for a suite of island arc basalts (IABs) from Kamchatka to investigate chromium isotope fractionation during magmatic processes in a subduction setting. The chromium isotopic data (δ<ce:sup loc=\"post\">53</ce:sup>Cr) for Kamchatka arc magmas range from –0.09 ± 0.02 ‰ to –0.16 ± 0.02 ‰ (2σ, n = 22). These magmatic rocks exhibit a positive correlation between MgO content and Ni, Cr contents, as well as CaO/Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf> ratios, which suggests that they undergo olivine and pyroxene fractional crystallization. However, δ<ce:sup loc=\"post\">53</ce:sup>Cr shows no correlation with Cr, Ni, or MgO contents, nor with CaO/Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf> ratios. Ionic modeling and Rayleigh fractionation modeling reveals minimal effects of fractional crystallization on the δ<ce:sup loc=\"post\">53</ce:sup>Cr factors in these arc magmas (Δ<ce:sup loc=\"post\">53</ce:sup>Cr<ce:inf loc=\"post\">crystal-melt</ce:inf>: +0.0001 ‰ to + 0.009 ‰), and probably IABs in general. Furthermore, the lack of correlation between δ<ce:sup loc=\"post\">53</ce:sup>Cr and the melting fraction suggests that partial melting also has a limited influence on Cr isotopic compositions. The δ<ce:sup loc=\"post\">53</ce:sup>Cr values also show no correlation with <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr ratios, chromium contents, or fluid-mobile elements (e.g., Ba/Th, B/Nb, As*/Ce), indicating that slab-derived fluids have a minimal effect on the chromium isotope composition of the mantle source of arc magmas. Notably, however, the majority of these samples show δ<ce:sup loc=\"post\">53</ce:sup>Cr similar to Bulk Silicate Earth, and are statistically higher compared to those observed in mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs). Melting and Rayleigh fractionation models suggest that the high δ<ce:sup loc=\"post\">53</ce:sup>Cr values in these arc magmas may be attributed to partial melting and fractional crystallization under higher magmatic oxygen fugacity conditions compared to those in MORBs and OIBs. This is consistent with their higher Fe<ce:sup loc=\"post\">3+</ce:sup>/Σ Fe ratios and Δ log fO<ce:inf loc=\"post\">2</ce:inf> (QFM) values, emphasizing the role of varying oxygen fugacity on chromium isotope fractionation in terrestrial basalts. This study highlights the potential of chromium isotopes as a powerful tool for tracing planetary oxygen fugacity environments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"34 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877859","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":"Rubidium and potassium isotope compositions of enstatite meteorites: implications for the evolution of their parent body(ies)","authors":"Baoliang Wang ,&nbsp;Frédéric Moynier ,&nbsp;Yan Hu","doi":"10.1016/j.gca.2025.04.007","DOIUrl":"10.1016/j.gca.2025.04.007","url":null,"abstract":"<div><div>Enstatite meteorites, including enstatite chondrites and enstatite achondrites (e.g., aubrites), formed under highly reducing conditions in the solar system. Enstatite chondrites underwent progressive thermal metamorphism from petrologic type 3 to type 6, potentially leading to vaporization and redistribution of volatile elements. Coupled Rb and K isotopic analyses of enstatite meteorites could provide complementary insights into the inherent isotopic variability and volatile depletion processes. In this study, we present Rb and K isotopic compositions for a suite of enstatite meteorites, including sixteen enstatite chondrites spanning metamorphic grades from 3 to 6, as well as four aubrites. Type 3 enstatite chondrites exhibit isotopic compositions similar to those of Earth for both Rb and K, which further underscores the isotopic resemblance between Earth and enstatite chondrites. From type 3–4 to type 5–6, the examined enstatite chondrites generally show a trend towards heavier Rb and K isotopic compositions, indicating volatilization and redistribution of Rb and K during open system thermal metamorphism of the parent body(ies). One EH5 (St. Marks) and two EL6 (Pillistfer and Atlanta) samples deviate from this trend with light K isotope compositions, which may result from an interplay of evaporation, vapor transport and recondensation. On the other hand, the Rb and K isotopic variations in aubrites—which originated from the melting and fractional crystallization of enstatite chondrite-like parent body(ies)—likely reflect more complex processes, possibly involving a combination of plagioclase-bearing melt extraction, magmatic differentiation, core segregation, and the back-condensation of volatiles after impact volatilization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 63-74"},"PeriodicalIF":4.5,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838916","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":"Biogenic iron minerals as a potential survival mechanism for nitrate-reducing iron-oxidizing bacteria","authors":"Han Li ,&nbsp;Kuan Cheng ,&nbsp;Ying Zhang ,&nbsp;Xiaomin Li ,&nbsp;Xiao Zhu ,&nbsp;Yundang Wu ,&nbsp;Guojun Chen ,&nbsp;Yang Yang ,&nbsp;Chao Guo ,&nbsp;Tongxu Liu","doi":"10.1016/j.gca.2025.04.010","DOIUrl":"10.1016/j.gca.2025.04.010","url":null,"abstract":"<div><div>Microaerophilic and phototrophic iron-oxidizing bacteria (FeOB) deal with the threat of cell encrustation by developing effective survival strategies, such as the production of extracellular organic structures for preferential nucleation. However, nitrate-reducing iron-oxidizing (NRFO) bacteria are not reported to have similar survival strategies. In this context, goethite and magnetite were chosen as biogenic iron minerals to evaluate their role in the survival mechanism of <em>Acidovorax</em> sp. BoFeN1. The NRFO kinetics results revealed that the added goethite and magnetite increased Fe(II) oxidation extent from 2.85 mM to 4.22 mM and 4.21 mM, while the extent of nitrate reduction was increased from 0.66 mM to 1.07 mM and 1.03 mM. The addition of goethite and magnetite did not promote microbial heterotrophic nitrate reduction without Fe(II), but accelerated the reaction between nitrite and Fe(II) in the chemodenitrification experiments. This suggested that goethite and magnetite facilitated the biological and chemical Fe(II) oxidation during the microbial NRFO process. Mineralogical analyses revealed that goethite and magnetite serve as nucleation sites for Fe precipitation. Electrochemical measurements revealed that goethite and magnetite elevated Fe(II) reactivity by decreasing its redox potential and corrosion potential. Therefore, goethite and magnetite promoted microbial NRFO process by mitigating cell encrustation and elevating Fe(II) reactivity. Since goethite and magnetite are typical secondary minerals of <em>Acidovorax</em> sp. BoFeN1, the production of biogenic iron mineral may be a survival strategy to prevent cell encrustation and maintain metabolic activity. The current findings provide novel insights into the survival mechanism of NRFO bacteria and related Fe-N cycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 53-62"},"PeriodicalIF":4.5,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838915","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":"Submicron-scale craters on Chang’e-5 lunar soils: records of complex space weathering processes","authors":"Lixin Gu ,&nbsp;Yangting Lin ,&nbsp;Yongjin Chen ,&nbsp;Yuchen Xu ,&nbsp;Xu Tang ,&nbsp;Jinhua Li","doi":"10.1016/j.gca.2025.04.004","DOIUrl":"10.1016/j.gca.2025.04.004","url":null,"abstract":"<div><div>Hyper-velocity impacts are dominant agents in the physical and chemical alteration of lunar surface materials. Natural small-scale craters on lunar soils provide an opportunity to understand the impact process and specific space weathering effects on minerals, however, they have not been systematically studied. Here, we report the morphology and microstructure of submicron-scale craters on Chang’e-5 lunar soils. Craters are found only on a few soil grains. Most identified craters exhibit large diameter-to-depth (D/d) ratios (&gt;3) or are spatially clustered, indicating that they are formed by secondary ejecta rather than primary micrometeoroid impacts. Advanced electron microscopy investigations revealed that the microstructures of these craters are complex. Craters on the surfaces of two pyroxenes and one olivine have continuous nanophase iron (npFe⁰)-bearing rims that extend over the crater and beyond over the crystal substrate, even when covered by an impact-produced redeposition layer. These features provide reliable evidence of solar wind exposure prior to the impact events that formed the craters. The possibility cannot be ruled out that the npFe⁰ particles present in these craters were previously produced by solar wind irradiation and not by impact. However, no clear signs are observed to establish the chronological order of formation of npFe⁰ particles in other craters studied. Furthermore, a crater on ilmenite has a minimum D/d value of 2.6, suggesting that this crater is likely formed by a primary micrometeoroid impact. Some unusual euhedral and elongated npFe⁰ particles observed on the crater floor may also have been produced earlier by solar wind irradiation and retained in the crater during subsequent impact. Shock melting and vapor deposition may also contribute to npFe⁰ formation by reduction during impact. Our findings imply that secondary impacts can also have a high velocity (1–2.38 km/s lunar escape velocity) and play a more crucial role in the microstructural and chemical changes of lunar soils than previously recognized. Moreover, the formation of npFe⁰ particles in submicron-scale craters may involve multiple processes, such as solar wind irradiation, shock melting, and vapor deposition, and their effects can be superimposed. These new formation processes of npFe⁰ particles are universal and fundamental to the evolution of materials on the Moon and other airless planetary bodies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 139-151"},"PeriodicalIF":4.5,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877860","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}