Geochimica et Cosmochimica Acta最新文献

{"title":"Sedimentary vanadium depletion under sulfidic conditions: Implications for (paleo)redox proxy applications","authors":"Niels A.G.M. van Helmond ,&nbsp;Olga M. Żygadłowska ,&nbsp;Wytze K. Lenstra ,&nbsp;Robin Klomp ,&nbsp;Christoph Humborg ,&nbsp;Daniel J. Conley ,&nbsp;Mike S.M. Jetten ,&nbsp;Caroline P. Slomp","doi":"10.1016/j.gca.2025.01.022","DOIUrl":"10.1016/j.gca.2025.01.022","url":null,"abstract":"<div><div>Sedimentary concentrations of redox-sensitive trace metals are widely used to reconstruct past ocean redox conditions. Vanadium (V) has great potential as a (paleo)redox proxy, due to its strong redox-dependent speciation (+III, +IV, +V) and the increased sedimentary sequestration of its more reduced species. The geochemistry of V in sulfide-rich marine environments is not yet well understood, however, hampering the use of V as a (paleo)redox proxy. Here, we present V data for two coastal systems, with bottom water redox conditions ranging from oxic to euxinic, to further constrain V geochemistry. Our sedimentary record from a eutrophic coastal marine basin (Scharendijke basin, Lake Grevelingen, the Netherlands), covering the last decade, shows distinct enrichments in molybdenum (Mo) and organic carbon (C_org) but depletions in V during seasonal bottom water euxinia, which can be discerned due to the exceptionally high sedimentation rate at our study site (up to 20 cm yr⁻¹). A seasonal study for the same coastal basin confirms this trend and reveals the accumulation of V, iron (Fe) and manganese (Mn) in the water column during summer euxinia. We conclude that the slow kinetics of V reduction to V(III) and subsequent precipitation as (oxy)hydroxide V(OH)_3(s) likely provide the opportunity for V to escape sedimentary sequestration during summer euxinia, resulting in the observed sedimentary V depletion. Sediments from three sites with contrasting bottom water redox conditions (oxic, seasonally hypoxic, euxinic) in the eutrophic Stockholm Archipelago, show a similar trend as that of Lake Grevelingen, with decreasing V concentrations and increasing Mo and C_org concentrations as bottom water conditions become more reducing. This confirms that our findings for Lake Grevelingen are not site-specific and are likely a generic feature of euxinic coastal systems with high sulfide concentrations (&gt; 0.5 mmol L⁻¹) near the sediment surface and high rates of anaerobic degradation of organic matter. Our results show that co-occurring sedimentary Mo and C_org enrichments and V depletion (or absence or suppression of an enrichment) are indicators of strongly sulfidic conditions in such settings. Finally, we show that maxima in sedimentary molar V/Mn ratios correlate with strongly reducing conditions. This finding contrasts with prior work on V/Mn ratios as a (paleo)redox proxy, implying that further research is necessary.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 238-253"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055425","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":"Effects of microbial alteration of oceanic crust on sulfur cycling in hydrothermal systems","authors":"Sarah N. Moriarty ,&nbsp;Emma Bertran ,&nbsp;James W. Dottin III ,&nbsp;James Farquhar ,&nbsp;David T. Johnston ,&nbsp;Stephen J. Piercey ,&nbsp;Dennis Sánchez-Mora ,&nbsp;Michael G. Babechuk ,&nbsp;Jason B. Sylvan ,&nbsp;John W. Jamieson","doi":"10.1016/j.gca.2024.11.031","DOIUrl":"10.1016/j.gca.2024.11.031","url":null,"abstract":"<div><div>The accumulation of continental-derived sediment along mid-ocean ridges can influence sub-seafloor hydrothermal fluid circulation, including fluid composition, and the composition of associated mineral accumulations at the seafloor. The intermediate spreading-rate Juan de Fuca Ridge, off the west coast of North America, hosts both sedimented and sediment-free hydrothermal systems (Middle Valley and Axial Volcano, respectively), as well a hydrothermal system which occurs at the outer extent of continental-derived turbiditic sediment accumulation (Endeavour Hydrothermal Vent Field). The seafloor at Endeavour is mostly sediment-free and consists of basaltic lava flows. However, previously reported hydrothermal vent fluid compositions suggest the presence of buried sediment. Here, we compare S isotope ratios (³³S/³²S and ³⁴S/³²S) of hydrothermal chimney and talus samples, as well as sediments, from these three varyingly sedimented hydrothermal sites on the Juan de Fuca Ridge to S isotope ratios from hydrothermal deposits along the fast spreading archetypical East Pacific Rise in order to investigate the geological controls and microbial influence on hydrothermal S cycling. Using a combined isotopic mixing and fractionation model in Δ³³S and δ³⁴S space, we demonstrate that reduced S within sediments does not provide a significant contribution to the S budget of hydrothermal systems in sedimented environments on the Juan de Fuca Ridge. Instead, our data indicate that variations in S isotope compositions within and between vent fields reflects different degrees of sub-seafloor microbial crustal alteration and kinetic fractionations associated with reduction of seawater sulfate. The degree of microbially induced S isotope fractionation can be linked to intensity of crustal alteration and therefore age of the hydrothermal system. Our results illustrate the added value of a multiple S isotope approach to investigating S cycling in hydrothermal systems, and that the influence of microbial activity on hydrothermal systems extends well below the seafloor.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 107-121"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683558","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":"Element Redistribution and Age Resetting in Shock-Deformed Zircon from the Chicxulub Impact Structure","authors":"Jiawei Zhao ,&nbsp;Long Xiao ,&nbsp;Zhiyong Xiao ,&nbsp;Xiang Wu ,&nbsp;Qi He ,&nbsp;Jialong Hao ,&nbsp;Ruiying Li ,&nbsp;Yangting Lin","doi":"10.1016/j.gca.2025.01.021","DOIUrl":"10.1016/j.gca.2025.01.021","url":null,"abstract":"<div><div>Zircon has been used to chronicle the geological evolution of the Earth and other planetary bodies. In some circumstances the U-Pb radioisotopic system in zircon can be completely reset by shock metamorphism (e.g. high-pressure phase formation and reversion, and recrystallization), erasing the initial crystallization record and instead recording the impact age. These behaviors of element redistribution accompanied with structure variation in shocked zircon provide pivotal evidence to unravel the extreme impact processes. However, the contributions from a variety of shock effects to element redistribution within shocked zircons are not clear due to the complicated and protracted metamorphic processes associated with an impact event. Here we use high-resolution Nano secondary ion mass spectrometry (NanoSIMS) to show that zircon grains from the Chicxulub impact structure that contain microstructural features such as planar/irregular fractures, zircon twins, reidite and zircon granules, record three main types of element redistribution processes related to shock metamorphism and post-impact modification. The first is the preferential yttrium (Y) enrichments at the zircon-reidite boundaries that is closely related to the formation of the high-pressure polymorph reidite, but the primary zoning is preserved in reidite-bearing zircon. The second process involves shock-related heating, resulting in the solid-state transformation from reidite-bearing zircon to granular zircon, and the growth of neo-formed zircon granules. This process facilitates the loss of radiogenic lead (Pb) and allows the retain of primary zoning of uranium (U) in granular zircon due to the different element diffusion properties, thus providing the chance to date the impact event. Thirdly, the studied zircon grains within the Chicxulub impact structure experienced post-impact hydrothermal alteration to varying degrees by localized element incorporation of additional yttrium (Y), titanium (Ti), uranium (U), lead (Pb) and phosphorus (P). The U-Pb systematics altered by post-impact hydrothermal processes reveal a generally discordant line affected by the external input of U and common Pb, which could be an alternative mechanism of localized age resetting happened in shocked zircon grains. Particularly, this study demonstrates the systematic characteristics of element redistribution in shocked zircons that experienced the sequential metamorphic processes from reidite formation to growth of zircon granules, and subsequent hydrothermal alteration within the Chicxulub impact structure. These findings provide the effective constraints for behaviors and mechanisms of element redistribution and age resetting in zircon under extreme shock and post-impact metamorphic conditions in terrestrial impact craters.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 219-237"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684049","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":"Mechanism of mineral adsorption enhancing the reduction of hexavalent chromium by natural organic matter","authors":"Peng Zhang ,&nbsp;Yiran Liu ,&nbsp;Yingxiao Tian ,&nbsp;Chenglong Yu ,&nbsp;Songhu Yuan","doi":"10.1016/j.gca.2025.03.011","DOIUrl":"10.1016/j.gca.2025.03.011","url":null,"abstract":"<div><div>Natural organic matter (NOM) serves a crucial electron reservoir for the reduction of hexavalent chromium (Cr(VI)) in subsurface environments. However, the influence of mineral adsorption on Cr(VI) reduction by NOM remains poorly understood, despite the widespread interaction among NOM, mineral matrices and Cr(VI) in natural environments. In this study, aluminum oxides (Al₂O₃) and Fe oxyhydroxides (such as ferrihydrite) were chosen as representative minerals to investigate how mineral adsorption influences on the reduction of Cr(VI) by both native and reduced NOM across a pH range of 5–9. Results of this study showed that the extent of Cr(VI) reduction (10 μM) was 1.5–11.1 % in the native NOM (12 mg/L) system, while it increased to 10.6–19.4 % in the native NOM-Al₂O₃ systems and to 19.4–25.4 % in the native NOM-ferrihydrite systems. Similarly, the extent of Cr(VI) reduction was 16.7–23.1 % in the reduced NOM system, while it increased to 17.5–38.3 % in the reduced NOM-Al₂O₃ systems and to 30–54.9 % in the reduced NOM-ferrihydrite systems. This enhancement effect increased with higher amounts of Al₂O₃ and ferrihydrite but diminished as the solution pH increased from 5 to 9. The enhancement of Cr(VI) reduction by Fe oxyhydroxides at the same dosage followed by the sequence: ferrihydrite &gt; lepidocrocite &gt; goethite &gt; hematite. In NOM system alone, phenolic moieties in NOM mainly contributed to Cr(VI) reduction. In NOM-Al₂O₃/Fe oxyhydroxide systems, mineral adsorption shifted the reaction site from solution phase to mineral surface, subsequently inducing oxidative polymerization of polyphenolic compounds in NOM, which generated more phenolic moieties that further facilitated the reduction of Cr(VI). Additionally, Fe oxyhydroxides served as electron shuttles, facilitating electron transfer from NOM to Cr(VI). This study highlights a previously unrecognized catalytic role of mineral adsorption in enhancing Cr(VI) reduction by NOM in subsurface environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 32-43"},"PeriodicalIF":4.5,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643488","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":"Metallogeny of subcontinental lithospheric mantle driven by sulfide-saturated pyroxenite-forming melts: evidence from the Balmuccia peridotite massif","authors":"Bartosz Pieterek ,&nbsp;Magdalena Matusiak-Małek ,&nbsp;Riccardo Tribuzio ,&nbsp;Marina Lazarov ,&nbsp;Magdalena Pańczyk ,&nbsp;Harald Strauss ,&nbsp;Thomas Kuhn ,&nbsp;Zbigniew Czupyt ,&nbsp;Jakub Ciazela ,&nbsp;Stefan Weyer","doi":"10.1016/j.gca.2025.03.007","DOIUrl":"10.1016/j.gca.2025.03.007","url":null,"abstract":"<div><div>Focused melt flow is a common phenomenon in the subcontinental lithospheric mantle. Although it exerts significant control on the magmatic differentiation of the upper mantle, its role in metal transport remains poorly constrained. To improve our understanding of the subcontinental mantle metallogeny, we investigated the Balmuccia massif of the Ivrea-Verbano Zone (Italian Alps), which consists of fresh mantle peridotites that experienced a prolonged period of multistage melt intrusions. As a result, this massif hosts two suites of pyroxenite dykes, known as Cr-diopside and Al-augite pyroxenites, which enable us to provide undisturbed insights into mantle metallogeny. Here, through scrutiny of the pyroxenite dykes and their contacts with mantle peridotites, we provide insights into the sulfide and associated chalcophile metals (e.g., Cu and Ag) distributions. We demonstrate that the Balmuccia mantle pyroxenites are enriched in magmatic sulfides and sulfide-loving elements compared to the Balmuccia mantle peridotites. In particular, the pyroxenites contain up to 8 times more Cu (on average 227 ± 58 ppm; 1SD; n = 8) than the mantle peridotites (29 ± 20 ppm Cu; n = 20). Additionally, we found that each sulfide phase has distinct S-Fe isotopic signatures among sulfides. Such differentiation indicates that the S-Fe isotopic fractionation is most likely controlled by the mass-dependent fractionation that follows the (re)crystallization under high-T subsolidus magmatic conditions.</div><div>The increased amount of sulfides and associated chalcophile metals (Cu and Ag) within the studied pyroxenites evidence the heterogeneous distribution of sulfides and metals in the subcontinental lithospheric mantle, similarly to observations from other pyroxenite dykes within mantle rocks and metasomatized mantle xenoliths. Specifically, we estimate that from 12% to 42% of the Cu and from 11% to 40% of the Ag of the upper mantle inventory could be accumulated within mantle pyroxenites. Our results indicate that mantle pyroxenites constitute a critical metal reservoir for subcontinental lithospheric metallogeny.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 248-266"},"PeriodicalIF":4.5,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724028","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":"Barium uptake and isotope fractionation by a marine diatom: Implications for oceanic barium cycle","authors":"Yu-Te Hsieh ,&nbsp;Po-Kai Yang ,&nbsp;Tung-Yuan Ho","doi":"10.1016/j.gca.2025.03.006","DOIUrl":"10.1016/j.gca.2025.03.006","url":null,"abstract":"<div><div>Barium (Ba) is a nutrient-type element in the ocean and is commonly used as a tracer for reconstructing marine productivity. Despite recent developments in Ba stable isotope analysis and growing research interest, the controls on biological Ba uptake and isotope fractionation remain largely unknown. This study presents a series of culture experiments using the model marine diatom <em>Thalassiosira weissflogii</em> to explore biological Ba uptake contributing to pelagic barite (BaSO₄) formation and its associated isotope fractionation for the first time. The results show that Ba cell quotas (Ba/P) are positively correlated with Ba concentrations in the culture medium, with slopes influenced by diatom-specific growth rates under high and low light levels. Similar trends in Ba, Ca, and Sr uptake suggest that Ba is likely taken up passively through Ca transporters, as a leakage of seawater Ba into the cells. This study also investigates Ba/C ratios in <em>Thalassiosira weissflogii</em> for the first time, revealing significantly lower ratios (down to 43500-fold) compared to those observed in marine field particles. This finding suggests that additional Ba sources are required to sustain particulate Ba flux associated with export production in marine water columns. The Ba isotope compositions of the cultured species indicate preferential uptake of isotopically lighter Ba from seawater, with isotope fractionation Δ¹³⁸Ba_bio-sw values ranging from −0.47 ‰ to −0.14 ‰ as Ba concentrations in the medium increase from 90 to 200 nmol/kg. The fractionation pattern is independent of the growth rates. The Ba isotope results from cultured diatoms provide the first evidence explaining the mismatch between Ba isotope fractionation factors in pelagic and laboratory-precipitated barite, suggesting that initial isotope fractionation from seawater through biological uptake can lead to a more negative fractionation factor in pelagic barite than that observed in laboratory-precipitated barite. Considering the Ba/C ratios between cultured diatoms and sediment traps, biological uptake is unlikely to be the sole or primary source of Ba for pelagic barite formation. This study provides the first constraint on marine diatom Ba cell quotas and their isotope fractionation factors, emphasizing the need to investigate the contribution of Ba from other sources (e.g., microbial processes) and the associated isotope fractionation during pelagic barite formation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 238-247"},"PeriodicalIF":4.5,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724017","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":"Exogenous iron mitigates photo-facilitation of soil organic matter","authors":"Yongli Wen ,&nbsp;Jiali Wu ,&nbsp;Xueting Wen ,&nbsp;Zhuoyue Zhang ,&nbsp;Jian Wang ,&nbsp;Guanghui Yu ,&nbsp;Xinhua He ,&nbsp;Maohong Xu ,&nbsp;Man Cheng ,&nbsp;Wenjuan Liu ,&nbsp;Jian Xiao","doi":"10.1016/j.gca.2025.03.010","DOIUrl":"10.1016/j.gca.2025.03.010","url":null,"abstract":"<div><div>Subalpine meadow soil carbon (C) is susceptible to ultraviolet B (UV-B) radiation, yet the mechanisms of UVB-induced soil organic C (SOC) photodegradation and the influence of iron (Fe) on this susceptibility remain largely unknown. In this study, soils from the southeastern (SE) and northwestern (NW) slopes of a subalpine meadow were exposed to three UVB treatments, elevated (ele-UVB, ∼120 μW·cm⁻²), ambient (amb-UVB, ∼60 μW·cm⁻²), or attenuated (no-UVB, 0 μW·cm⁻²), to assess the effects of UV radiation and Fe addition on SOC mineralization. A two-phase lignin incubation experiment was then conducted to elucidate the mechanism by which Fe influences the abiotic and biotic processes of lignin photodegradation. Results showed that ele-UVB increased SOC degradation by 137 % and 34 % in the SE and NW soils, respectively. Lignin phenols underwent significant photochemical degradation, which was mitigated by Fe addition. Furthermore, our findings revealed that photo-facilitation (i.e., microbial decomposition) significantly contributed to lignin photodegradation, releasing over 5 times more CO₂ than abiotic degradation did. This occurred mainly due to the depolymerization of lignin macromolecules, which increased the substrate availability for microbes, rather than shifts in microbial community composition. Fe impacted photo-facilitation by binding with lignin derivatives, reducing microbial accessibility and limiting their decomposition. These findings highlight the intricate interactions among UV-B radiation, Fe, and microbial processes in SOC turnover, offering critical insights for soil C management under global environmental change scenarios.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 1-11"},"PeriodicalIF":4.5,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629384","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":"Loss and accretion of moderately volatile elements K and Na in Australasian microtektites from Antarctica","authors":"M. Del Rio ,&nbsp;L. Folco ,&nbsp;E. Mugnaioli ,&nbsp;S. Goderis ,&nbsp;M. Masotta","doi":"10.1016/j.gca.2025.03.005","DOIUrl":"10.1016/j.gca.2025.03.005","url":null,"abstract":"<div><div>Recent studies on alkali metals, Ar-, Fe- and K-isotope distribution in Australasian microtektites have revealed the complex interplay of multiple fractionation processes in establishing their moderately volatile elements record, particularly in those deposited in Antarctica, most distal from the hypothetical source crater. To provide a better understanding of moderately volatile elements fractionation during microtektite formation, we studied the distribution of K, Na, Rb and Cs in twenty-seven Australasian microtektites from Antarctica ranging in size from 180 to 680 µm. Compositional profiles were determined using electron probe microanalyses (major elements) and laser ablation-inductively coupled plasma-mass spectrometry (trace elements), following a petrographic study at the nanoscopic scale by means of scanning and transmission electron microscopy. The Australasian microtektites from Antarctica contain nanometer-sized, partly digested lechatelierite inclusions and rare vesicles, and record significant moderately volatile elements depletion (Na₂O = 0.30 ± 0.07 (1σ) wt%; K₂O = 0.94 ± 0.25 (1σ) wt%) relative to: i) upper continental crust (Na₂O = 3.46 wt%; K₂O = 3.45 wt%), ii) microtektites from deep sea sediments (Na₂O = 1.15 ± 0.43 (1σ) wt%; K₂O = 2.47 ± 0.82 (1σ) wt%), and iii) Australasian tektites (Na₂O = 1.20 ± 0.19 (1σ) wt%; K₂O = 2.43 ± 0.24 (1σ) wt%). They are also characterized by moderately volatile elements enrichments at their rims (up to ∼2x for K₂O; ∼1.6x for Na₂O), and the enrichment factor typically decreases with increasing diameter. Lastly, there is an inverse correlation between bulk Na₂O content (but not K₂O) and diameter. We propose that the most distal Antarctic microtektites originated as impact melt droplets and not as vapor condensate spherules. Their moderately volatile elements geochemical budget was established through three subsequent stages of fractionation in the context of a hypervelocity impact. 1) Gross Na and K and other moderately volatile elements loss which occurred during the melting and vaporization of the target precursor materials. 2) Re-accretion of Na, K and other moderately volatile elements from the condensation of a hot gas envelope of vaporized target materials onto volatile depleted droplets cores. 3) Size-controlled partial evaporation of (mainly) Na, caused by aerodynamic drag heating, during deceleration from high ejection velocities either during the decoupling from the hot gas envelope in ambient air, or during atmospheric re-entry, as suggested by alkalis and Fe-isotope data in the literature. The late accretion of K vapor also provides plausible explanations for the contamination by extraneous Ar and K-isotopic systematics reported in the literature.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 212-228"},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724018","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":"Abiotic and biotic transformation of petroleum hydrocarbons coupled with redox cycling of structural iron in clay mineral","authors":"Yuan Liu ,&nbsp;Hongyu Chen ,&nbsp;Yizhi Sheng ,&nbsp;Weiguo Hou ,&nbsp;Wenhui Zhang ,&nbsp;Wenhui Hu ,&nbsp;Hailiang Dong","doi":"10.1016/j.gca.2025.02.038","DOIUrl":"10.1016/j.gca.2025.02.038","url":null,"abstract":"<div><div>Geothermal systems are hot spots for interaction among minerals, microorganisms, and hydrocarbons. Coupled hydrocarbon transformation and redox cycling of iron in minerals is important to ecosystem functions but remains poorly understood. This work studied abiotic transformation of petroleum hydrocarbons by reactive oxygen species produced upon oxygenation of a reduced clay mineral (nontronite NAu-2). Subsequently, the impact of such abiotic petroleum-clay interactions on coupled reduction of structural Fe(III) in clay mineral and petroleum transformation was studied under anaerobic condition. In the abiotic phase, hydrocarbons in a crude oil sample were oxidized by hydroxyl radicals (^<img>OH) generated upon oxygenation of reduced NAu-2, forming partially oxygenated compounds with hydroxyl, carbonyl, and carboxyl groups. In the subsequent bio-reduction experiments, these more bioavailable compounds significantly enhanced Fe(III) bio-reduction by a thermophilic microbial community enriched from a terrestrial hot spring. In particular, <em>Sphingomonas</em> and <em>Phyllobacterium</em> were enriched, both of which possessed genes for anaerobic hydrocarbon activation and Fe(III) reduction. Notably, the thermophilic community possessed more genes for breaking down C, H, and O-containing compounds. In contrast, when the same thermophilic community was exposed to the original (unoxidized) petroleum hydrocarbons, they possessed more genes for degrading C and H compounds. These findings enhance our understanding of the important role of minerals in regulating hydrocarbon transformation and in shaping subsurface microbial community.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 44-63"},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666482","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":"Planktic foraminifera record the succession of anaerobic metabolisms in particle microenvironments across a pelagic oxygen gradient","authors":"Shannon C. Doherty ,&nbsp;Catherine V. Davis ,&nbsp;Jennifer S. Fehrenbacher","doi":"10.1016/j.gca.2025.03.008","DOIUrl":"10.1016/j.gca.2025.03.008","url":null,"abstract":"<div><div>Microenvironments inside marine organic particles can host anaerobic microbial respiration outside of ocean anoxic zones, but these environments are challenging to directly observe. We present evidence that the planktic foraminifer <em>Globorotaloides hexagonus</em> inhabits a particle microenvironment and suggest that their shell chemistry records anaerobic microbial metabolisms inside particles. We propose a novel interpretation of intrashell trends in Ba/Ca, Mn/Ca, and Zn/Ca ratios as signals of denitrification, Mn respiration, and sulfate reduction. We measure these trace elements in <em>G. hexagonus</em> collected from discrete depth horizons across a pelagic oxygen gradient in the Eastern Tropical North Pacific. Using this intrashell trace element framework, we find that denitrification may have occurred inside particles throughout the water column, and that Mn respiration and sulfate reduction may have occurred inside particles throughout the oxygen minimum zone. Our results have implications for budgets of nitrogen, sulfur, manganese, and other trace elements in regions with expanding oxygen minimum zones and suggest a new method of interpreting intrashell trends in trace element-to-calcium ratios in planktic foraminifera.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 267-276"},"PeriodicalIF":4.5,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666529","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}