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 > lepidocrocite > goethite > 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.
{"title":"Mechanism of mineral adsorption enhancing the reduction of hexavalent chromium by natural organic matter","authors":"Peng Zhang , Yiran Liu , Yingxiao Tian , Chenglong Yu , 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 (Al<sub>2</sub>O<sub>3</sub>) 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-Al<sub>2</sub>O<sub>3</sub> 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-Al<sub>2</sub>O<sub>3</sub> systems and to 30–54.9 % in the reduced NOM-ferrihydrite systems. This enhancement effect increased with higher amounts of Al<sub>2</sub>O<sub>3</sub> 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 > lepidocrocite > goethite > hematite. In NOM system alone, phenolic moieties in NOM mainly contributed to Cr(VI) reduction. In NOM-Al<sub>2</sub>O<sub>3</sub>/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}
Pub Date : 2025-03-13DOI: 10.1016/j.gca.2025.03.010
Yongli Wen , Jiali Wu , Xueting Wen , Zhuoyue Zhang , Jian Wang , Guanghui Yu , Xinhua He , Maohong Xu , Man Cheng , Wenjuan Liu , Jian Xiao
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.
{"title":"Exogenous iron mitigates photo-facilitation of soil organic matter","authors":"Yongli Wen , Jiali Wu , Xueting Wen , Zhuoyue Zhang , Jian Wang , Guanghui Yu , Xinhua He , Maohong Xu , Man Cheng , Wenjuan Liu , 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<sup>−2</sup>), ambient (amb-UVB, ∼60 μW·cm<sup>−2</sup>), or attenuated (no-UVB, 0 μW·cm<sup>−2</sup>), 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 CO<sub>2</sub> 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}
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 (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, Sphingomonas and Phyllobacterium 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.
{"title":"Abiotic and biotic transformation of petroleum hydrocarbons coupled with redox cycling of structural iron in clay mineral","authors":"Yuan Liu, Hongyu Chen, Yizhi Sheng, Weiguo Hou, Wenhui Zhang, Wenhui Hu, Hailiang Dong","doi":"10.1016/j.gca.2025.02.038","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.038","url":null,"abstract":"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 (<ce:sup loc=\"post\"><ce:glyph name=\"rad\"></ce:glyph></ce:sup>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, <ce:italic>Sphingomonas</ce:italic> and <ce:italic>Phyllobacterium</ce:italic> 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.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"48 1","pages":""},"PeriodicalIF":5.0,"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}
Pub Date : 2025-03-12DOI: 10.1016/j.gca.2025.03.008
Shannon C. Doherty, Catherine V. Davis, Jennifer S. Fehrenbacher
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 Globorotaloides hexagonus 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 G. hexagonus 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.
{"title":"Planktic foraminifera record the succession of anaerobic metabolisms in particle microenvironments across a pelagic oxygen gradient","authors":"Shannon C. Doherty, Catherine V. Davis, Jennifer S. Fehrenbacher","doi":"10.1016/j.gca.2025.03.008","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.008","url":null,"abstract":"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 <ce:italic>Globorotaloides hexagonus</ce:italic> 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 <ce:italic>G. hexagonus</ce:italic> 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.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"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":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-08DOI: 10.1016/j.gca.2025.03.003
Michael Fettweis, Saumya Silori, Rieko Adriaens, Xavier Desmit
Particulate (POC) and dissolved organic carbon (DOC) concentration, clay mineral content and composition and the suspended particulate matter (SPM) concentration have been analyzed in water samples taken along transects from the high turbid nearshore to the low turbid offshore on the North Sea shelf. The suspended POC has been classified into a mineral-associated (POCmineral), a slowly degrading (POCslow) and a fresh fraction (POCfresh). The POCmineral has been estimated based on the clay mineral composition and on literature data of the mineral specific surface area per g and the OC content per specific surface area. It consists of organic molecules adsorbed onto mineral surfaces and is thereby the most refractory fraction. The POCfresh content (% of POCfresh in SPM) has been calculated using the semi-empirical POC-SPM model of Fettweis et al. (2022) and is intrinsically labile. The POCslow content is refractory with variable rates of degradation. The total POC content of the SPM was between 2 and 11%, from which about 0.3–6.6% (0.1–2.1%) was POCfresh in spring (resp., winter). The POCmineral content was between 0.4% and 1.1% and decreased towards the offshore, meaning that the POC offshore is less refractory than nearshore. The organic molecules adsorbed onto clay minerals, are dynamically exchanging with the DOC, and thus influencing its fate and concentration. However this process is not sufficient to explain the increasing POC/DOC ratio with increasing SPM concentration, which is further explained by primary production, advection and diffusion, density gradients and seabed erosion. Our results highlight the difficulty and the necessity of estimating the respective sample-POC and DOC concentrations, fluxes and fates along SPM concentration gradients in coastal zones. This is needed as organo-mineral interactions influence the vertical dynamics and horizontal transport of SPM and have an impact on particles and organic carbon fluxes.
{"title":"Clay minerals and the stability of organic carbon in suspension along coastal to offshore transects","authors":"Michael Fettweis, Saumya Silori, Rieko Adriaens, Xavier Desmit","doi":"10.1016/j.gca.2025.03.003","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.003","url":null,"abstract":"Particulate (POC) and dissolved organic carbon (DOC) concentration, clay mineral content and composition and the suspended particulate matter (SPM) concentration have been analyzed in water samples taken along transects from the high turbid nearshore to the low turbid offshore on the North Sea shelf. The suspended POC has been classified into a mineral-associated (POC<ce:inf loc=\"post\">mineral</ce:inf>), a slowly degrading (POC<ce:inf loc=\"post\">slow</ce:inf>) and a fresh fraction (POC<ce:inf loc=\"post\">fresh</ce:inf>). The POC<ce:inf loc=\"post\">mineral</ce:inf> has been estimated based on the clay mineral composition and on literature data of the mineral specific surface area per g and the OC content per specific surface area. It consists of organic molecules adsorbed onto mineral surfaces and is thereby the most refractory fraction. The POC<ce:inf loc=\"post\">fresh</ce:inf> content (% of POC<ce:inf loc=\"post\">fresh</ce:inf> in SPM) has been calculated using the semi-empirical POC-SPM model of Fettweis et al. (2022) and is intrinsically labile. The POC<ce:inf loc=\"post\">slow</ce:inf> content is refractory with variable rates of degradation. The total POC content of the SPM was between 2 and 11%, from which about 0.3–6.6% (0.1–2.1%) was POC<ce:inf loc=\"post\">fresh</ce:inf> in spring (resp., winter). The POC<ce:inf loc=\"post\">mineral</ce:inf> content was between 0.4% and 1.1% and decreased towards the offshore, meaning that the POC offshore is less refractory than nearshore. The organic molecules adsorbed onto clay minerals, are dynamically exchanging with the DOC, and thus influencing its fate and concentration. However this process is not sufficient to explain the increasing POC/DOC ratio with increasing SPM concentration, which is further explained by primary production, advection and diffusion, density gradients and seabed erosion. Our results highlight the difficulty and the necessity of estimating the respective sample-POC and DOC concentrations, fluxes and fates along SPM concentration gradients in coastal zones. This is needed as organo-mineral interactions influence the vertical dynamics and horizontal transport of SPM and have an impact on particles and organic carbon fluxes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"183 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666341","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}
Pub Date : 2025-03-07DOI: 10.1016/j.gca.2025.03.004
Carolina Dantas Cardoso , Raphaël Pik , Antonio Caracausi , Sæmundur Ari Halldórsson , Andri Stefánsson , Laurent Zimmermann , Guillaume Paris , Andrea Ricci , Hreinn Hjartarson
<div><div>Iceland is a location of geological interest due to the combination of upwelling mantle plume and divergent plate boundary, which resulted in the formation of its extensive surface area (>100,000 km<sup>2</sup>) that rises above sea-level. This unique setting facilitates assessing the role of the underlying mantle plume and tectonic activity on crust-forming processes. Helium isotopes provide a useful tool in this regard, as they can identify physical processes and resolve deep and shallow fluid sources in the crust. In Iceland, the highest <sup>3</sup>He/<sup>4</sup>He for geothermal fluids are found in Vestfirðir with values up to 29 R<sub>a</sub> (where R<sub>a</sub> is the <sup>3</sup>He/<sup>4</sup>He of air), more than 110 km away from current active rift zones. Such locations are key to understand the extent of mantle degassing processes associated with the high buoyant Icelandic mantle plume. Other off-rift regions, such as most of North Iceland, have not been extensively investigated, despite the widespread presence of geothermal activity. Although North Iceland has been volcanically inactive for the past 0.8 Ma, severe earthquake hazards associated with mature and partially on-land transform zones have occurred, rendering the monitoring of the full tectonic-hydrogeochemical system of societal importance. Our study in North Iceland aimed to (i) assess temporal variations in helium isotopic signatures in low-T geothermal water and their relationship with regional earthquakes, (ii) diminish the helium isotope data gap in geothermal fluids of this region, and (iii) elucidate both local and regional processes controlling the He isotope systematics in this region as a case study for other off-rift contexts on Earth. In order to achieve these goals, we report helium isotope time series data collected from June 2020 to October 2022 from a borehole in Hafralækur, Aðaldalur valley (95 samples collected on a near-weekly basis), along with an isotope survey (δ<sup>2</sup>H-<sup>3</sup>He/<sup>4</sup>He-δ<sup>13</sup>C<sub>TDIC</sub>-δ<sup>18</sup>O-δ<sup>34</sup>S<sub>SO4</sub>) of North Iceland geothermal fluids (T < 130 °C, n = 36 samples). The results indicate a large regional variability in helium isotope ratios (4 to 27 R<sub>a</sub>) that is comparable to the entire range evident in geothermal fluids across Iceland (∼1 to 29 R<sub>a</sub>) where the maximum <sup>3</sup>He/<sup>4</sup>He signature is among the highest measured in geothermal fluids from oceanic and continental hotspots globally. Several processes, both on regional and local scales, are needed to account for this large range: (i) influence of a deeply-derived mantle flux evidenced by a high <sup>3</sup>He/<sup>4</sup>He mantle component, degassing via fault systems, (ii) release of local radiogenic helium components, potentially associated with seismic events along the Dalvík Lineament, and (iii) local groundwater mixing, for example evident at the Hafralækur sit
{"title":"Helium isotopes in geothermal fluids reveal off-rift plume degassing and localized seismicity-induced processes in North Iceland","authors":"Carolina Dantas Cardoso , Raphaël Pik , Antonio Caracausi , Sæmundur Ari Halldórsson , Andri Stefánsson , Laurent Zimmermann , Guillaume Paris , Andrea Ricci , Hreinn Hjartarson","doi":"10.1016/j.gca.2025.03.004","DOIUrl":"10.1016/j.gca.2025.03.004","url":null,"abstract":"<div><div>Iceland is a location of geological interest due to the combination of upwelling mantle plume and divergent plate boundary, which resulted in the formation of its extensive surface area (>100,000 km<sup>2</sup>) that rises above sea-level. This unique setting facilitates assessing the role of the underlying mantle plume and tectonic activity on crust-forming processes. Helium isotopes provide a useful tool in this regard, as they can identify physical processes and resolve deep and shallow fluid sources in the crust. In Iceland, the highest <sup>3</sup>He/<sup>4</sup>He for geothermal fluids are found in Vestfirðir with values up to 29 R<sub>a</sub> (where R<sub>a</sub> is the <sup>3</sup>He/<sup>4</sup>He of air), more than 110 km away from current active rift zones. Such locations are key to understand the extent of mantle degassing processes associated with the high buoyant Icelandic mantle plume. Other off-rift regions, such as most of North Iceland, have not been extensively investigated, despite the widespread presence of geothermal activity. Although North Iceland has been volcanically inactive for the past 0.8 Ma, severe earthquake hazards associated with mature and partially on-land transform zones have occurred, rendering the monitoring of the full tectonic-hydrogeochemical system of societal importance. Our study in North Iceland aimed to (i) assess temporal variations in helium isotopic signatures in low-T geothermal water and their relationship with regional earthquakes, (ii) diminish the helium isotope data gap in geothermal fluids of this region, and (iii) elucidate both local and regional processes controlling the He isotope systematics in this region as a case study for other off-rift contexts on Earth. In order to achieve these goals, we report helium isotope time series data collected from June 2020 to October 2022 from a borehole in Hafralækur, Aðaldalur valley (95 samples collected on a near-weekly basis), along with an isotope survey (δ<sup>2</sup>H-<sup>3</sup>He/<sup>4</sup>He-δ<sup>13</sup>C<sub>TDIC</sub>-δ<sup>18</sup>O-δ<sup>34</sup>S<sub>SO4</sub>) of North Iceland geothermal fluids (T < 130 °C, n = 36 samples). The results indicate a large regional variability in helium isotope ratios (4 to 27 R<sub>a</sub>) that is comparable to the entire range evident in geothermal fluids across Iceland (∼1 to 29 R<sub>a</sub>) where the maximum <sup>3</sup>He/<sup>4</sup>He signature is among the highest measured in geothermal fluids from oceanic and continental hotspots globally. Several processes, both on regional and local scales, are needed to account for this large range: (i) influence of a deeply-derived mantle flux evidenced by a high <sup>3</sup>He/<sup>4</sup>He mantle component, degassing via fault systems, (ii) release of local radiogenic helium components, potentially associated with seismic events along the Dalvík Lineament, and (iii) local groundwater mixing, for example evident at the Hafralækur sit","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"395 ","pages":"Pages 12-31"},"PeriodicalIF":4.5,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629448","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}
To better constrain the Ca isotope effect during partial melting of Earth’s mantle, we used ab initio molecular dynamic simulations to calculate the equilibrium mineral-silicate melt Ca isotope fractionation factors for the major Ca-bearing minerals of the upper mantle (orthopyroxene, clinopyroxene, olivine, and garnet), as well as plagioclase. We found that mineral-melt Ca isotope fractionation factors are dependent on pressure, temperature, and mineral major element compositions, but not the silicate melt composition. Specifically, our calculations show that under equilibrium, clinopyroxene has a slightly heavier Ca isotope composition compared to silicate melt, consistent with the inference of published research that studied the Ca isotope effects during basaltic magma evolution.
{"title":"Mineral-melt calcium isotope fractionation factors constrained using ab initio molecular dynamics simulations and their implications to calcium isotope effects during partial melting in the upper mantle","authors":"Yonghui Li, Justin Hardin, Wenzhong Wang, Zhongqing Wu, Shichun Huang","doi":"10.1016/j.gca.2025.02.032","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.032","url":null,"abstract":"To better constrain the Ca isotope effect during partial melting of Earth’s mantle, we used <ce:italic>ab initio</ce:italic> molecular dynamic simulations to calculate the equilibrium mineral-silicate melt Ca isotope fractionation factors for the major Ca-bearing minerals of the upper mantle (orthopyroxene, clinopyroxene, olivine, and garnet), as well as plagioclase. We found that mineral-melt Ca isotope fractionation factors are dependent on pressure, temperature, and mineral major element compositions, but not the silicate melt composition. Specifically, our calculations show that under equilibrium, clinopyroxene has a slightly heavier Ca isotope composition compared to silicate melt, consistent with the inference of published research that studied the Ca isotope effects during basaltic magma evolution.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"34 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666342","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}
Pub Date : 2025-03-05DOI: 10.1016/j.gca.2025.02.020
Ekanshu Mallick, Kelsey Prissel, Kevin Righter, Colin R.M. Jackson
Nitrogen is important in planetary evolution because it is essential to life and the most abundant element in Earth’s atmosphere. Here, we investigate how core formation affects the distribution of N within accreting terrestrial planets. We conducted laser-heated diamond anvil cell experiments (LH-DAC) over a wide range of high pressure–temperature-compositional (PTX) conditions (38–103 GPa, 2728–5609 K, −1.95 to −1.03 ΔIW, 0.5–3.7 NBO/T) to study nitrogen partitioning in metal-silicate systems. Combining our data with existing low and high PT results, we developed a nitrogen partitioning model applicable from early accretion to extreme PT stages associated with giant impacts. We test the robustness of our model by accurately predicting nitrogen partitioning in a multi-anvil experiment conducted independently at 15 GPa, 2573 K with oxygen fugacity of −2.5 ΔIW. Our model shows that increasing pressure, oxygen fugacity, and N concentration in the alloy make nitrogen more siderophile, while increasing temperature, oxygen and silicon contents in the alloy, and the SiO2 content of the silicate melt make nitrogen less siderophile. Application of our model to core formation conditions under oxidized and reduced scenarios suggest that nitrogen can be siderophile or lithophile under low PT conditions but exhibits a neutral partitioning at high PT conditions (> 100 GPa, 5000 K) over a wide range of bulk planet compositions. Using our model, along with partitioning models for S and C, we examine how core formation scenarios can fractionate C/N and S/N ratios in the BSE. Our model suggests that backreaction of volatile rich cores from reduced, smaller impactors (sub-Mars-sized) within deep magma oceans can impart a wide range of C/N and S/N ratios on the magma ocean. We find that the amount of silicate entrainment has a strong control on elemental fractionations imparted to the magma oceans. Elevated C/N and S/N ratios are associated with larger degrees of silicate entrainment, and vice versa. Thus, Earth’s apparent depletion of N may relate to its volatiles being reprocessed within deep magma oceans, possibly during the end stages of accretion.
{"title":"The fate of nitrogen in deep magma oceans","authors":"Ekanshu Mallick, Kelsey Prissel, Kevin Righter, Colin R.M. Jackson","doi":"10.1016/j.gca.2025.02.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.020","url":null,"abstract":"Nitrogen is important in planetary evolution because it is essential to life and the most abundant element in Earth’s atmosphere. Here, we investigate how core formation affects the distribution of N within accreting terrestrial planets. We conducted laser-heated diamond anvil cell experiments (LH-DAC) over a wide range of high pressure–temperature-compositional (PTX) conditions (38–103 GPa, 2728–5609 K, −1.95 to −1.03 ΔIW, 0.5–3.7 NBO/T) to study nitrogen partitioning in metal-silicate systems. Combining our data with existing low and high PT results, we developed a nitrogen partitioning model applicable from early accretion to extreme PT stages associated with giant impacts. We test the robustness of our model by accurately predicting nitrogen partitioning in a multi-anvil experiment conducted independently at 15 GPa, 2573 K with oxygen fugacity of −2.5 ΔIW. Our model shows that increasing pressure, oxygen fugacity, and N concentration in the alloy make nitrogen more siderophile, while increasing temperature, oxygen and silicon contents in the alloy, and the SiO<ce:inf loc=\"post\">2</ce:inf> content of the silicate melt make nitrogen less siderophile. Application of our model to core formation conditions under oxidized and reduced scenarios suggest that nitrogen can be siderophile or lithophile under low PT conditions but exhibits a neutral partitioning at high PT conditions (> 100 GPa, 5000 K) over a wide range of bulk planet compositions. Using our model, along with partitioning models for S and C, we examine how core formation scenarios can fractionate C/N and S/N ratios in the BSE. Our model suggests that backreaction of volatile rich cores from reduced, smaller impactors (sub-Mars-sized) within deep magma oceans can impart a wide range of C/N and S/N ratios on the magma ocean. We find that the amount of silicate entrainment has a strong control on elemental fractionations imparted to the magma oceans. Elevated C/N and S/N ratios are associated with larger degrees of silicate entrainment, and vice versa. Thus, Earth’s apparent depletion of N may relate to its volatiles being reprocessed within deep magma oceans, possibly during the end stages of accretion.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666413","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}
Pub Date : 2025-03-04DOI: 10.1016/j.gca.2025.03.001
Pratigya J. Polissar, A.Tyler Karp, William J. D’Andrea
Plant leaf waxes and their isotopic composition are important tracers of ecological, environmental, and climate variability, with strong preservation potential in sedimentary archives. However, they represent an integrated, and often complicated, signal of vegetation and hydrology within a watershed. Here, we report a new approach for examining complex mixtures of n-alkanes in sediments and their isotope values: non-negative matrix factorization (NMF). NMF identifies the endmembers in a mixture from the integrated n-alkane data and provides quantitative information on the relative importance of those endmembers across samples. We apply this approach to a synthetic dataset and two previously published datasets to illustrate its uses. Our application of NMF to re-analyse previously published data reveals new insights into past climate and ecological change. We demonstrate that NMF allows a user to 1) identify potential mixing problems, 2) evaluate which specific compounds in a mixture carry the isotope signal that can best address a given scientific objective, 3) determine compound concentrations after excluding contributions from particular endmember sources, and 4) calculate isotope values of different sources. NMF provides a quantitative approach for evaluating the influence of endmember mixing on molecular concentrations and isotope values within a dataset. The re-analysis of two published datasets reveals new quantitative insight into Holocene Arctic climate and Neogene vegetation change.
{"title":"Mixed messages: Unmixing sedimentary molecular distributions reveals source contributions and isotopic values","authors":"Pratigya J. Polissar, A.Tyler Karp, William J. D’Andrea","doi":"10.1016/j.gca.2025.03.001","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.001","url":null,"abstract":"Plant leaf waxes and their isotopic composition are important tracers of ecological, environmental, and climate variability, with strong preservation potential in sedimentary archives. However, they represent an integrated, and often complicated, signal of vegetation and hydrology within a watershed. Here, we report a new approach for examining complex mixtures of <ce:italic>n</ce:italic>-alkanes in sediments and their isotope values: non-negative matrix factorization (NMF). NMF identifies the endmembers in a mixture from the integrated <ce:italic>n</ce:italic>-alkane data and provides quantitative information on the relative importance of those endmembers across samples. We apply this approach to a synthetic dataset and two previously published datasets to illustrate its uses. Our application of NMF to re-analyse previously published data reveals new insights into past climate and ecological change. We demonstrate that NMF allows a user to 1) identify potential mixing problems, 2) evaluate which specific compounds in a mixture carry the isotope signal that can best address a given scientific objective, 3) determine compound concentrations after excluding contributions from particular endmember sources, and 4) calculate isotope values of different sources. NMF provides a quantitative approach for evaluating the influence of endmember mixing on molecular concentrations and isotope values within a dataset. The re-analysis of two published datasets reveals new quantitative insight into Holocene Arctic climate and Neogene vegetation change.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"70 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666344","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}
Pub Date : 2025-03-04DOI: 10.1016/j.gca.2025.03.002
Maria A. Dias, Ralf Dohmen, Harald Behrens
Knowledge of Fe-Mg interdiffusion coefficients (<ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf>) in orthopyroxene (opx) is relevant for diffusion chronometry as well as for thermometers based on Fe-Mg exchange between opx and other common mafic minerals. We extended the existing data set for <ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf> to quantify the effect of the molar fraction of Fe, <ce:italic>X</ce:italic><ce:inf loc="post">Fe</ce:inf> = Fe/(Fe + Mg) = 0.1 to 0.4, and oxygen fugacity, <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> = 10<ce:sup loc="post">-7</ce:sup> to 10<ce:sup loc="post">-11</ce:sup> Pa, in the temperature range, <ce:italic>T</ce:italic> = 950–1100 °C, where we build up on our recently developed experimental and analytical approach. Thin film diffusion couples using different natural opx with different trace element contents were annealed in vertical gas mixing furnaces. The diffusion profiles were extracted by acquiring backscattered electron images on foils cut from the samples using a focused ion beam-scanning electron microscope. We found complex interplays between the effect of <ce:italic>T</ce:italic>, <ce:italic>X</ce:italic><ce:inf loc="post">Fe</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> on <ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf>. The effect of <ce:italic>X</ce:italic><ce:inf loc="post">Fe</ce:inf> increases with <ce:italic>T</ce:italic> for <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> = 10<ce:sup loc="post">-7</ce:sup> to 10<ce:sup loc="post">-9</ce:sup> Pa but decreases with <ce:italic>T</ce:italic> for more reducing conditions. For <ce:italic>T</ce:italic> > 1000 °C and <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> > 10<ce:sup loc="post">-10</ce:sup> Pa, <ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf> depends on <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> and <ce:italic>X</ce:italic><ce:inf loc="post">Fe</ce:inf>. For these conditions <ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf> is described by an activation energy of 284 ± 19 kJ/mol. For <ce:italic>T</ce:italic> = 950 °C to 1000 °C and for <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> < 10<ce:sup loc="post">-10</ce:sup> Pa, <ce:italic>D</ce:italic><ce:inf loc="post">Fe-Mg</ce:inf> seemingly ceases to depend on <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf>, indicating a change of the diffusion mechanism, and is described by an activation energy of 246 ± 78 kJ/mol. Based on these diffusion data, we propose a qualitative point defect model for opx where the majority point defects changes over the explored Fe content, <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> and <ce:italic>T</ce:italic> conditions from vacancies on the metal site/electron holes to vacancies on the metal site/Fe<ce:sup loc="post">3+</ce:sup> to Mg interstitials/electrons, each one responsible for a different effect of <ce:italic>f</ce:
{"title":"Fe-Mg interdiffusion in orthopyroxene: Complex interdependencies of temperature, composition and oxygen fugacity","authors":"Maria A. Dias, Ralf Dohmen, Harald Behrens","doi":"10.1016/j.gca.2025.03.002","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.002","url":null,"abstract":"Knowledge of Fe-Mg interdiffusion coefficients (<ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf>) in orthopyroxene (opx) is relevant for diffusion chronometry as well as for thermometers based on Fe-Mg exchange between opx and other common mafic minerals. We extended the existing data set for <ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf> to quantify the effect of the molar fraction of Fe, <ce:italic>X</ce:italic><ce:inf loc=\"post\">Fe</ce:inf> = Fe/(Fe + Mg) = 0.1 to 0.4, and oxygen fugacity, <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> = 10<ce:sup loc=\"post\">-7</ce:sup> to 10<ce:sup loc=\"post\">-11</ce:sup> Pa, in the temperature range, <ce:italic>T</ce:italic> = 950–1100 °C, where we build up on our recently developed experimental and analytical approach. Thin film diffusion couples using different natural opx with different trace element contents were annealed in vertical gas mixing furnaces. The diffusion profiles were extracted by acquiring backscattered electron images on foils cut from the samples using a focused ion beam-scanning electron microscope. We found complex interplays between the effect of <ce:italic>T</ce:italic>, <ce:italic>X</ce:italic><ce:inf loc=\"post\">Fe</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> on <ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf>. The effect of <ce:italic>X</ce:italic><ce:inf loc=\"post\">Fe</ce:inf> increases with <ce:italic>T</ce:italic> for <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> = 10<ce:sup loc=\"post\">-7</ce:sup> to 10<ce:sup loc=\"post\">-9</ce:sup> Pa but decreases with <ce:italic>T</ce:italic> for more reducing conditions. For <ce:italic>T</ce:italic> > 1000 °C and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> > 10<ce:sup loc=\"post\">-10</ce:sup> Pa, <ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf> depends on <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> and <ce:italic>X</ce:italic><ce:inf loc=\"post\">Fe</ce:inf>. For these conditions <ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf> is described by an activation energy of 284 ± 19 kJ/mol. For <ce:italic>T</ce:italic> = 950 °C to 1000 °C and for <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> < 10<ce:sup loc=\"post\">-10</ce:sup> Pa, <ce:italic>D</ce:italic><ce:inf loc=\"post\">Fe-Mg</ce:inf> seemingly ceases to depend on <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>, indicating a change of the diffusion mechanism, and is described by an activation energy of 246 ± 78 kJ/mol. Based on these diffusion data, we propose a qualitative point defect model for opx where the majority point defects changes over the explored Fe content, <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> and <ce:italic>T</ce:italic> conditions from vacancies on the metal site/electron holes to vacancies on the metal site/Fe<ce:sup loc=\"post\">3+</ce:sup> to Mg interstitials/electrons, each one responsible for a different effect of <ce:italic>f</ce:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"92 1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666343","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}
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