Pub Date : 2025-12-20DOI: 10.1016/j.gca.2025.12.042
Martin Wille , Olaf Dellwig , Florian Kurzweil , Helge W. Arz , Leo Armingeon , Qasid Ahmad
<div><div>Molybdenum concentrations and stable isotope compositions have been extensively applied to marine sediments for palaeo-redox reconstruction. While the open ocean Mo isotope signature is conservative on time scales of several million years, and depends on the changing global isotopic mass balance between input and output fluxes, large Mo isotope variability over smaller time scales has been identified in organic-rich sediments. In addition to changing dissolved sulfide levels and deep-water ventilation times, the varying extent of Fe and Mn oxide shuttling is also considered to be a cause of short-term variability in Mo isotopes. Here we present the Mo isotope composition of well-dated sediments from the redox-stratified Landsort Deep (Baltic Sea) covering the current warm period and the medieval climate anomaly. These modern sediments provide the unique opportunity to directly link water column redox conditions, derived from instrumental time-series, to the sedimentary Mo isotope record. We observe an overall lower Mo isotopic composition (av. δ<sup>98</sup>Mo −0.21 ‰) during longer-lasting bottom water hypoxia between ∼ 1955 and 2000 CE than during weakly sulfidic interruptions and sapropel formation since ∼ 2000 CE (av. δ<sup>98</sup>Mo + 0.63 ‰). Such lower δ<sup>98</sup>Mo signatures during hypoxia benefitted from intense Mn oxide-shuttling near the sediment/water interface. Sedimentary δ<sup>98</sup>Mo values as low as −0.94 ‰ compared to seawater, most likely required intense Mo isotope fractionation via repeated Mn oxide shuttling, aided by incomplete thiolation at a weakly sulfidic sediment/water interface, before Mo was finally sequestered from strongly sulfidic porewaters. Such combined Mo isotope fractionation is also seen in the weakly sulfidic and hypoxic water columns of the Landsort and Gotland Deeps, which suggests significant changes in Mo cycling depending on the presence of dissolved sulfide and Mn oxide. Based on comparable geochemical variations, similar redox dynamics could be also attested for the Landsort Deep sediments deposited during the medieval climate anomaly.</div><div>In comparison to other modern O<sub>2</sub>-deficient marine settings ranging from mildly reducing to strongly sulfidic conditions, the Landsort Deep sediments deposited during fluctuating sulfidic-hypoxic periods with intense shuttling of Mn oxides act as a distinct sink of isotopically light Mo from the ocean with overall lower δ<sup>98</sup>Mo compared to the marine Mo input flux. Widespread occurrence of Mn ores in organic matter-rich sediments throughout Earth’s history implies that dynamic redox conditions comparable to those in the Landsort Deep were more frequent. This could be particularly true for past periods of global warming, when the flooding of shelf areas promoted expansion of reducing bottom waters in epicontinental seas. Finally, the coupled Mo-Mn-S cycling during fundamental redox changes in such epicontinental settings, a
{"title":"Impact of strong redox shifts and manganese cycling on sedimentary molybdenum isotopes in stratified hypoxic/euxinic basins","authors":"Martin Wille , Olaf Dellwig , Florian Kurzweil , Helge W. Arz , Leo Armingeon , Qasid Ahmad","doi":"10.1016/j.gca.2025.12.042","DOIUrl":"10.1016/j.gca.2025.12.042","url":null,"abstract":"<div><div>Molybdenum concentrations and stable isotope compositions have been extensively applied to marine sediments for palaeo-redox reconstruction. While the open ocean Mo isotope signature is conservative on time scales of several million years, and depends on the changing global isotopic mass balance between input and output fluxes, large Mo isotope variability over smaller time scales has been identified in organic-rich sediments. In addition to changing dissolved sulfide levels and deep-water ventilation times, the varying extent of Fe and Mn oxide shuttling is also considered to be a cause of short-term variability in Mo isotopes. Here we present the Mo isotope composition of well-dated sediments from the redox-stratified Landsort Deep (Baltic Sea) covering the current warm period and the medieval climate anomaly. These modern sediments provide the unique opportunity to directly link water column redox conditions, derived from instrumental time-series, to the sedimentary Mo isotope record. We observe an overall lower Mo isotopic composition (av. δ<sup>98</sup>Mo −0.21 ‰) during longer-lasting bottom water hypoxia between ∼ 1955 and 2000 CE than during weakly sulfidic interruptions and sapropel formation since ∼ 2000 CE (av. δ<sup>98</sup>Mo + 0.63 ‰). Such lower δ<sup>98</sup>Mo signatures during hypoxia benefitted from intense Mn oxide-shuttling near the sediment/water interface. Sedimentary δ<sup>98</sup>Mo values as low as −0.94 ‰ compared to seawater, most likely required intense Mo isotope fractionation via repeated Mn oxide shuttling, aided by incomplete thiolation at a weakly sulfidic sediment/water interface, before Mo was finally sequestered from strongly sulfidic porewaters. Such combined Mo isotope fractionation is also seen in the weakly sulfidic and hypoxic water columns of the Landsort and Gotland Deeps, which suggests significant changes in Mo cycling depending on the presence of dissolved sulfide and Mn oxide. Based on comparable geochemical variations, similar redox dynamics could be also attested for the Landsort Deep sediments deposited during the medieval climate anomaly.</div><div>In comparison to other modern O<sub>2</sub>-deficient marine settings ranging from mildly reducing to strongly sulfidic conditions, the Landsort Deep sediments deposited during fluctuating sulfidic-hypoxic periods with intense shuttling of Mn oxides act as a distinct sink of isotopically light Mo from the ocean with overall lower δ<sup>98</sup>Mo compared to the marine Mo input flux. Widespread occurrence of Mn ores in organic matter-rich sediments throughout Earth’s history implies that dynamic redox conditions comparable to those in the Landsort Deep were more frequent. This could be particularly true for past periods of global warming, when the flooding of shelf areas promoted expansion of reducing bottom waters in epicontinental seas. Finally, the coupled Mo-Mn-S cycling during fundamental redox changes in such epicontinental settings, a","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 204-218"},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785257","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 : 2025-12-20DOI: 10.1016/j.gca.2025.12.047
A. Ollive, W. Geibert, J. Matthiessen, M. Alscher, M. Frank, J. Lachner, K. Stübner, F. Adolphi
{"title":"Processes controlling the authigenic 10Be/9Be ratio in the Arctic Ocean","authors":"A. Ollive, W. Geibert, J. Matthiessen, M. Alscher, M. Frank, J. Lachner, K. Stübner, F. Adolphi","doi":"10.1016/j.gca.2025.12.047","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.047","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"27 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796046","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 : 2025-12-20DOI: 10.1016/j.gca.2025.12.034
Robin Hintzen , Roland Hellmann , Vladimir V. Roddatis , Julia van Winden , Laurent Truche
<div><div>The reaction kinetics of reductive pyrite (FeS<sub>2</sub>) dissolution by H<sub>2</sub> is important to predict the long-term aqueous and gaseous sulfide release in underground hydrogen storage and other engineered subsurface sites. We investigated the rates of pyrite reduction based on sulfide formation as a function of temperature (60-150 °C), H<sub>2</sub> partial pressure (0-150 bar), and pH<sub>in situ</sub> (∼ 4-10) in deoxygenated 0.03 M NaCl solutions. The experiments used natural pyrite powder (ø = 50-100 µm) and were run in hydrothermal batch reactors made of either titanium or Dursan®-coated 316L stainless steel. After experimental durations of ∼ 700-900 h, dissolved S<sup>-II</sup><sub>(aq)</sub> concentrations measured by methylene blue spectrophotometry ranged from 10<sup>-5</sup> to 10<sup>-3</sup> M. Long-term pyrite dissolution and concomitant elevated S<sup>-II</sup><sub>(aq)</sub> concentrations were controlled by the formation of secondary pyrrhotite (Fe<sub>1-x</sub>S) and magnetite (Fe<sub>3</sub>O<sub>4</sub>), which prevented the ion activity product of FeS<sub>2</sub> from achieving rapid saturation. Conversely, in the absence of pyrrhotite and magnetite precipitation, the solutions rapidly equilibrated with respect to pyrite, resulting in low S<sup>-II</sup><sub>(aq)</sub> concentrations. Rates of reductive pyrite dissolution were determined at 12 h from total S<sup>-II</sup><sub>(aq+gas)</sub> concentration vs. time data and were found to increase with temperature and H<sub>2</sub>-partial pressure. The rate dependency on pH at 90 °C, 7 bar <em>P</em><sub>H2</sub> was regressed either with an asymmetric ‘V’-shaped (two rate-pH domains) or a ‘U’-shaped (three rate-pH domains) relation. For this reason, two separate kinetic rate laws were derived, based on the ‘U’-regression (<em>E<sub>a</sub></em> = 35.2 kJ mol<sup>-1</sup>):</div><div><span><math><mrow><mi>r</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>5.42</mn></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mn>35208</mn><mo>/</mo><mi>R</mi><mi>T</mi></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>P</mi><msub><mi>H</mi><mn>2</mn></msub></msub></mrow></mfenced></mrow><mrow><mn>0.37</mn></mrow></msup><mfenced><mrow><mn>1</mn><mo>-</mo><mfrac><mi>Q</mi><msub><mi>K</mi><mrow><mi>eq</mi></mrow></msub></mfrac></mrow></mfenced></mrow></math></span></div><div>or the ‘V’-regression (<em>E<sub>a</sub></em> = 29.4 kJ mol<sup>-1</sup>):</div><div><span><math><mrow><mi>r</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>5.13</mn></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mn>29370</mn><mo>/</mo><mi>R</mi><mi>T</mi></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>a</mi><msup><mrow><mi>H</mi></mrow><mo>+</mo></msup></msub></mrow></mfenced></mrow><mrow><mn>0.13</mn></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>P</mi><msub><mi>H</mi><mn>2</mn></msub></msub></mrow></mfenced></mrow><mrow><mn>0.37</mn></mrow>
{"title":"Experimental kinetic rate laws for aqueous pyrite reduction at underground hydrogen storage conditions (60–150 °C, up to 150 bar H2)","authors":"Robin Hintzen , Roland Hellmann , Vladimir V. Roddatis , Julia van Winden , Laurent Truche","doi":"10.1016/j.gca.2025.12.034","DOIUrl":"10.1016/j.gca.2025.12.034","url":null,"abstract":"<div><div>The reaction kinetics of reductive pyrite (FeS<sub>2</sub>) dissolution by H<sub>2</sub> is important to predict the long-term aqueous and gaseous sulfide release in underground hydrogen storage and other engineered subsurface sites. We investigated the rates of pyrite reduction based on sulfide formation as a function of temperature (60-150 °C), H<sub>2</sub> partial pressure (0-150 bar), and pH<sub>in situ</sub> (∼ 4-10) in deoxygenated 0.03 M NaCl solutions. The experiments used natural pyrite powder (ø = 50-100 µm) and were run in hydrothermal batch reactors made of either titanium or Dursan®-coated 316L stainless steel. After experimental durations of ∼ 700-900 h, dissolved S<sup>-II</sup><sub>(aq)</sub> concentrations measured by methylene blue spectrophotometry ranged from 10<sup>-5</sup> to 10<sup>-3</sup> M. Long-term pyrite dissolution and concomitant elevated S<sup>-II</sup><sub>(aq)</sub> concentrations were controlled by the formation of secondary pyrrhotite (Fe<sub>1-x</sub>S) and magnetite (Fe<sub>3</sub>O<sub>4</sub>), which prevented the ion activity product of FeS<sub>2</sub> from achieving rapid saturation. Conversely, in the absence of pyrrhotite and magnetite precipitation, the solutions rapidly equilibrated with respect to pyrite, resulting in low S<sup>-II</sup><sub>(aq)</sub> concentrations. Rates of reductive pyrite dissolution were determined at 12 h from total S<sup>-II</sup><sub>(aq+gas)</sub> concentration vs. time data and were found to increase with temperature and H<sub>2</sub>-partial pressure. The rate dependency on pH at 90 °C, 7 bar <em>P</em><sub>H2</sub> was regressed either with an asymmetric ‘V’-shaped (two rate-pH domains) or a ‘U’-shaped (three rate-pH domains) relation. For this reason, two separate kinetic rate laws were derived, based on the ‘U’-regression (<em>E<sub>a</sub></em> = 35.2 kJ mol<sup>-1</sup>):</div><div><span><math><mrow><mi>r</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>5.42</mn></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mn>35208</mn><mo>/</mo><mi>R</mi><mi>T</mi></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>P</mi><msub><mi>H</mi><mn>2</mn></msub></msub></mrow></mfenced></mrow><mrow><mn>0.37</mn></mrow></msup><mfenced><mrow><mn>1</mn><mo>-</mo><mfrac><mi>Q</mi><msub><mi>K</mi><mrow><mi>eq</mi></mrow></msub></mfrac></mrow></mfenced></mrow></math></span></div><div>or the ‘V’-regression (<em>E<sub>a</sub></em> = 29.4 kJ mol<sup>-1</sup>):</div><div><span><math><mrow><mi>r</mi><mo>=</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>5.13</mn></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo><mn>29370</mn><mo>/</mo><mi>R</mi><mi>T</mi></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>a</mi><msup><mrow><mi>H</mi></mrow><mo>+</mo></msup></msub></mrow></mfenced></mrow><mrow><mn>0.13</mn></mrow></msup><msup><mrow><mfenced><mrow><msub><mi>P</mi><msub><mi>H</mi><mn>2</mn></msub></msub></mrow></mfenced></mrow><mrow><mn>0.37</mn></mrow>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 169-190"},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796047","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 : 2025-12-20DOI: 10.1016/j.gca.2025.12.044
Qinyuan Qu, Zhongwei Wang, Benjamin Chetelat, Zhengrong Wang, Qingchuan Liu, Mei Sun, Wei Yuan, Hongming Cai, Jianfeng Liu, Pengxue Gai, Yi Liu, Wang Zheng, Ruoyu Sun, Cong-Qiang Liu, Jiubin Chen
{"title":"Lithogenic control on zinc stable isotopes in riverine systems: The importance of carbonate dissolution","authors":"Qinyuan Qu, Zhongwei Wang, Benjamin Chetelat, Zhengrong Wang, Qingchuan Liu, Mei Sun, Wei Yuan, Hongming Cai, Jianfeng Liu, Pengxue Gai, Yi Liu, Wang Zheng, Ruoyu Sun, Cong-Qiang Liu, Jiubin Chen","doi":"10.1016/j.gca.2025.12.044","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.044","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"181 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796050","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 : 2025-12-20DOI: 10.1016/j.gca.2025.12.021
Yanan Cheng, Jun Mu, Peizheng He, Cheng Cao, Shichao An, Can Zhang, Xiaoping Feng, Cheng Zhao, Xiao-Ming Liu
{"title":"K isotope behavior in topsoil from the southeastern margin of the Tibetan Plateau","authors":"Yanan Cheng, Jun Mu, Peizheng He, Cheng Cao, Shichao An, Can Zhang, Xiaoping Feng, Cheng Zhao, Xiao-Ming Liu","doi":"10.1016/j.gca.2025.12.021","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.021","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"19 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785258","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 : 2025-12-20DOI: 10.1016/j.gca.2025.12.037
Wonhee Lee , Donghwan Kim , Jihye Oh , Jonguk Kim , Chang Hwan Kim , Chan Hong Park , Jeongmin Kim , Yuyoung Lee , Hyunwoo Lee
Volatiles recycled via subduction can be partly stored within the sub-arc lithosphere, forming long-lived geochemical reservoirs. Northeast (NE) Asia possesses a unique geological context in which the subduction of the Pacific plate has profoundly influenced tectonic and magmatic processes, providing an opportunity to investigate the records of subducted components preserved within the metasomatized sub-continental lithospheric mantle (SCLM). Here we present noble gas (He, Ne, and Ar) and O isotope compositions of the Cenozoic intraplate basalts sampled from Ulleungdo (UD), Anyongbok (AYB), Dokdo (DD), and Shimheungtaek (SHT) volcanoes in the East Sea (Sea of Japan). The measured 3He/4He ratios (4.5 to 6.0 Ra) indicate that a dominant source of He might be the SCLM, although the atmospheric Ne and Ar isotope compositions reflect potential incorporation of atmospheric components at shallow-levels. The olivine δ18O values (4.29 to 6.45‰) further suggest that the mantle sources have been metasomatized by fluids/melts mostly derived from the 18O-enriched recycled crustal components. Geochemical comparisons between intraplate basalts from the East Sea and Hantangang (HT) regions reveal that magma generations possibly involved partial melting of the garnet-bearing asthenosphere mixed with melts from the fertile lithospheric mantle, with more pronounced metasomatic signatures in the East Sea. The spatial variations in noble gas isotopes within the NE Asian SCLM imply that the Pacific plate subduction during the Cenozoic has been a major factor in its metasomatic modifications. Our results demonstrate that residual metasomatized SCLM could serve as a significant repository for volatiles recycled through subduction processes, which can be later mobilized during intraplate volcanic activity.
{"title":"Metasomatized lithospheric mantle as a reservoir for recycled volatiles: Noble gas and oxygen isotope systematics in the East Sea","authors":"Wonhee Lee , Donghwan Kim , Jihye Oh , Jonguk Kim , Chang Hwan Kim , Chan Hong Park , Jeongmin Kim , Yuyoung Lee , Hyunwoo Lee","doi":"10.1016/j.gca.2025.12.037","DOIUrl":"10.1016/j.gca.2025.12.037","url":null,"abstract":"<div><div>Volatiles recycled via subduction can be partly stored within the sub-arc lithosphere, forming long-lived geochemical reservoirs. Northeast (NE) Asia possesses a unique geological context in which the subduction of the Pacific plate has profoundly influenced tectonic and magmatic processes, providing an opportunity to investigate the records of subducted components preserved within the metasomatized sub-continental lithospheric mantle (SCLM). Here we present noble gas (He, Ne, and Ar) and O isotope compositions of the Cenozoic intraplate basalts sampled from Ulleungdo (UD), Anyongbok (AYB), Dokdo (DD), and Shimheungtaek (SHT) volcanoes in the East Sea (Sea of Japan). The measured <sup>3</sup>He/<sup>4</sup>He ratios (4.5 to 6.0 Ra) indicate that a dominant source of He might be the SCLM, although the atmospheric Ne and Ar isotope compositions reflect potential incorporation of atmospheric components at shallow-levels. The olivine δ<sup>18</sup>O values (4.29 to 6.45‰) further suggest that the mantle sources have been metasomatized by fluids/melts mostly derived from the <sup>18</sup>O-enriched recycled crustal components. Geochemical comparisons between intraplate basalts from the East Sea and Hantangang (HT) regions reveal that magma generations possibly involved partial melting of the garnet-bearing asthenosphere mixed with melts from the fertile lithospheric mantle, with more pronounced metasomatic signatures in the East Sea. The spatial variations in noble gas isotopes within the NE Asian SCLM imply that the Pacific plate subduction during the Cenozoic has been a major factor in its metasomatic modifications. Our results demonstrate that residual metasomatized SCLM could serve as a significant repository for volatiles recycled through subduction processes, which can be later mobilized during intraplate volcanic activity.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 146-168"},"PeriodicalIF":5.0,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796048","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 : 2025-12-19DOI: 10.1016/j.gca.2025.12.032
Ruo-Lin Liu , Martin Yan Hei Li , Run-Sheng Yin , Mei-Fu Zhou , Jun-Hong Zhao
Vegetation is very important to the formation of pedosphere, and it enhances the release of metals from weathered mafic–ultramafic rocks, and facilitates the generation of economically important laterite deposits. Vegetation accumulates mercury (Hg) mainly through foliage uptake of gaseous Hg(0), and therefore vegetation-derived Hg displays negative Δ199Hg values, which enables Hg isotopes as effective proxy to trace the role of vegetation in supergene mineralization. In this study, we conducted mineralogical, elemental, and Hg isotopic analyses of two typical profiles from the Yuanjiang nickel (Ni) laterite deposit in SW China. Both profiles have concurrent negative Δ199Hg peaks (−0.65 to −0.39 ‰) above the Ni-enriched zones, even in the deep saprolite and saprock horizons, implying that (1) the laterite receives a substantial amount of Hg from vegetation; (2) the vegetation-derived materials could penetrate deep in laterite; and (3) vegetation may play a critical role in promoting Ni mobilization during weathering. Vegetation-derived materials, including organic matter, can significantly acidify the surface soils and generate local reducing environments, favoring the formation of mobile Ni (exchangeable, adsorbed and organic-bound Ni) through breakdown of silicate minerals and/or iron (Fe) oxides, and also facilitate the development of preferential flow pathways for vertical Ni leaching. Thus, Ni is depleted in upper vegetation-input zones and enriched in the lower zones through incorporation in Fe oxides and secondary silicate minerals. This work highlights the application of Hg isotopes to trace the influence of vegetation in laterite development, and sheds light on the role of vegetation in the genesis of Ni laterites, which is also important to understand the biogeochemical cycle of Ni during chemical weathering.
{"title":"Mercury isotope perspectives on vegetation-enhanced nickel mobilization and migration during laterite formation","authors":"Ruo-Lin Liu , Martin Yan Hei Li , Run-Sheng Yin , Mei-Fu Zhou , Jun-Hong Zhao","doi":"10.1016/j.gca.2025.12.032","DOIUrl":"10.1016/j.gca.2025.12.032","url":null,"abstract":"<div><div>Vegetation is very important to the formation of pedosphere, and it enhances the release of metals from weathered mafic–ultramafic rocks, and facilitates the generation of economically important laterite deposits. Vegetation accumulates mercury (Hg) mainly through foliage uptake of gaseous Hg(0), and therefore vegetation-derived Hg displays negative Δ<sup>199</sup>Hg values, which enables Hg isotopes as effective proxy to trace the role of vegetation in supergene mineralization. In this study, we conducted mineralogical, elemental, and Hg isotopic analyses of two typical profiles from the Yuanjiang nickel (Ni) laterite deposit in SW China. Both profiles have concurrent negative Δ<sup>199</sup>Hg peaks (−0.65 to −0.39 ‰) above the Ni-enriched zones, even in the deep saprolite and saprock horizons, implying that (1) the laterite receives a substantial amount of Hg from vegetation; (2) the vegetation-derived materials could penetrate deep in laterite; and (3) vegetation may play a critical role in promoting Ni mobilization during weathering. Vegetation-derived materials, including organic matter, can significantly acidify the surface soils and generate local reducing environments, favoring the formation of mobile Ni (exchangeable, adsorbed and organic-bound Ni) through breakdown of silicate minerals and/or iron (Fe) oxides, and also facilitate the development of preferential flow pathways for vertical Ni leaching. Thus, Ni is depleted in upper vegetation-input zones and enriched in the lower zones through incorporation in Fe oxides and secondary silicate minerals. This work highlights the application of Hg isotopes to trace the influence of vegetation in laterite development, and sheds light on the role of vegetation in the genesis of Ni laterites, which is also important to understand the biogeochemical cycle of Ni during chemical weathering.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 100-113"},"PeriodicalIF":5.0,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785260","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 : 2025-12-19DOI: 10.1016/j.gca.2025.12.039
Andrea Pezzera, Long Li, Richard A. Stern, D. Graham Pearson
<div><div>The nitrogen (N) isotope composition of world-wide diamonds shows considerable variability that is uncorrelated with carbon isotopes. Most of this variability is currently explained by different compositions of the N sources, although fractionation processes can nonetheless play a role. Because N in Earth’s mantle is overprinted by subduction as time progresses, we examined the N isotope composition of the Knee Lake diamond suite, hosted in volcaniclastic rocks erupted in the Neoarchean at ∼2.73 Ga, to try to obtain an older glimpse of N isotope variability. Secondary ion mass spectrometry analyses of 186 Knee Lake diamonds revealed extraordinarily varied N isotope compositions, expanding from the lowest (−46.8 ‰) to the highest (+31.8 ‰) values measured for terrestrial diamonds, strongly clustered around a median of −0.7 ‰. The median value advocate for a heavier-than modern δ<sup>15</sup>N composition of the Archean mantle, suggesting a secular change from a <sup>15</sup>N-enriched primordial composition. Whether some of the δ<sup>15</sup>N variability in the Knee Lake diamonds could have been inherited by crustal recycled or unmixed primordial sources, the range and discontinuous distribution of the most extreme values rule out an overall explanation as being formed by mixing of heterogeneous N sources and suggests the involvement of fractionation processes. The systematics of N concentration ([N]) and δ<sup>15</sup>N variations for most of the Knee Lake diamonds are permissive of a Rayleigh distillation process. Rayleigh distillation during kinetic isotope fractionation associated with the decomposition of N-phases could even produce the most <sup>15</sup>N-enriched compositions and the uncorrelated [N] and δ<sup>13</sup>C variability. However, Ryleigh fractionation cannot produce the most <sup>15</sup>N-depleted compositions. The extreme N isotope compositions in the Knee Lake diamond suite are correlated with crystal shape, the most negative δ<sup>15</sup>N values occurring in cuboid and the most positive in octahedral crystals. This suggests the operation of kinetic N fractionation processes related to different growth-surface structures or growth conditions. Despite the recognition of distinct N isotope compositions in different growth sectors in synthetic crystals, two mixed-habit Knee Lake diamonds show only a small growth-sector related N isotope variability. The only process we can model that is capable of producing the most <sup>15</sup>N-depleted values is diffusion along chemical gradients, whether pre-existing in the growth environment or generated by crystal growth under diffusion-limited conditions as indicated by the re-entrant, fibrous shape of some cuboid crystals. These observations highlight the complexity of nitrogen isotope geochemistry in the Earth mantle, and suggest that various kinetic effects may play a role in fractionating the N isotope compositions of some diamonds during their growth. The possibility of
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Pub Date : 2025-12-19DOI: 10.1016/j.gca.2025.12.023
Xikai Wang, Xiao-Ming Liu, Hana Jurikova, Daniela Henkel, Kun Wang, Mohsen Shakouri
{"title":"Potassium isotope fractionation in the cultured brachiopod Magellania venosa","authors":"Xikai Wang, Xiao-Ming Liu, Hana Jurikova, Daniela Henkel, Kun Wang, Mohsen Shakouri","doi":"10.1016/j.gca.2025.12.023","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.023","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"19 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785261","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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