Pub Date : 2025-12-23DOI: 10.1016/j.gca.2025.12.040
Darci Rush, Jan H. van Maarseveen, Jan A.J. Geenevasen, Erik Tegelaar, Jos Pureveen, Roel Klein Nijenhuis, Nick Westerveld, Md Mahbubul Islam, Adri C.T. van Duin, Stefan Schouten, Jaap S. Sinninghe Damsté
{"title":"Towards stable chemical fossils for anaerobic ammonium-oxidizing bacteria in palaeoenvironmental studies: novel cyclic aliphatic hydrocarbons as potential dia- and catagenetic products of ladderane lipids","authors":"Darci Rush, Jan H. van Maarseveen, Jan A.J. Geenevasen, Erik Tegelaar, Jos Pureveen, Roel Klein Nijenhuis, Nick Westerveld, Md Mahbubul Islam, Adri C.T. van Duin, Stefan Schouten, Jaap S. Sinninghe Damsté","doi":"10.1016/j.gca.2025.12.040","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.040","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823501","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 : 2025-12-23DOI: 10.1016/j.gca.2025.12.050
Guojun Chen , Yang Yang , Ke Zhang , Yan Ru , Zebin Hong , Xiaomin Li , Taicheng An , Pei Wang , Songxiong Zhong , Qi Wang , Shiwen Hu , Fangbai Li , Tongxu Liu
Basalt-derived paddy soils contain high concentrations of chromium (Cr) from basalt weathering. Considering the potential risks of available Cr to human health, the transformation of Cr in basalt-derived paddy soils has attracted worldwide attention. However, the mechanisms controlling the biogeochemical cycling of Cr in these soils remain unclear. Here, pot experiments were performed to investigate Cr migration and transformation throughout the flooding–drainage cycle. The dynamic changes in soil chemical (e.g., dissolved organic carbon (DOC), iron (Fe) (oxyhydr)oxides, sulfate, and nitrogen (N) species) and physical properties (e.g., UV–vis spectra, pore size distribution, and surface site concentrations) were investigated. The available Cr increased during flooding and decreased during drainage. Cr concentrations in rice grains exceeded the safety threshold, indicating high Cr availability in these soils and the associated risk to human health. A kinetic model was developed to unravel the key factors controlling Cr transformation. During flooding, the mobilization of the available Cr was primarily driven by Fe (oxyhydr)oxides (76.4%), with a smaller contribution from organic matter (OM) (23.6%). During drainage, the sequestration of the available Cr was similarly dominated by Fe (oxyhydr)oxides (76.6%), followed by OM (23.4%). Furthermore, within the Fe (oxyhydr)oxides, metastable Fe phases played a predominant role in the available Cr immobilization (accounting for 91.6% of the total Fe contribution), while stable Fe phases contributed the remaining 8.4%. These insights are vital for understanding Cr mobility and availability in paddy soils with a high geological background.
{"title":"Quantifying contributions of iron (oxyhydr)oxides and organic matter to chromium dynamics in paddy soils","authors":"Guojun Chen , Yang Yang , Ke Zhang , Yan Ru , Zebin Hong , Xiaomin Li , Taicheng An , Pei Wang , Songxiong Zhong , Qi Wang , Shiwen Hu , Fangbai Li , Tongxu Liu","doi":"10.1016/j.gca.2025.12.050","DOIUrl":"10.1016/j.gca.2025.12.050","url":null,"abstract":"<div><div>Basalt-derived paddy soils contain high concentrations of chromium (Cr) from basalt weathering. Considering the potential risks of available Cr to human health, the transformation of Cr in basalt-derived paddy soils has attracted worldwide attention. However, the mechanisms controlling the biogeochemical cycling of Cr in these soils remain unclear. Here, pot experiments were performed to investigate Cr migration and transformation throughout the flooding–drainage cycle. The dynamic changes in soil chemical (e.g., dissolved organic carbon (DOC), iron (Fe) (oxyhydr)oxides, sulfate, and nitrogen (N) species) and physical properties (e.g., UV–vis spectra, pore size distribution, and surface site concentrations) were investigated. The available Cr increased during flooding and decreased during drainage. Cr concentrations in rice grains exceeded the safety threshold, indicating high Cr availability in these soils and the associated risk to human health. A kinetic model was developed to unravel the key factors controlling Cr transformation. During flooding, the mobilization of the available Cr was primarily driven by Fe (oxyhydr)oxides (76.4%), with a smaller contribution from organic matter (OM) (23.6%). During drainage, the sequestration of the available Cr was similarly dominated by Fe (oxyhydr)oxides (76.6%), followed by OM (23.4%). Furthermore, within the Fe (oxyhydr)oxides, metastable Fe phases played a predominant role in the available Cr immobilization (accounting for 91.6% of the total Fe contribution), while stable Fe phases contributed the remaining 8.4%. These insights are vital for understanding Cr mobility and availability in paddy soils with a high geological background.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 134-145"},"PeriodicalIF":5.0,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823500","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 : 2025-12-22DOI: 10.1016/j.gca.2025.12.049
Fang Qian, Yi Wang, Kassandra M. Costa, Sune G. Nielsen
The thallium isotopic composition (ε 205Tl) of seawater is a promising proxy for global oceanic redox conditions due to its strong association with manganese oxide burial. Previous studies have linked ε205Tl variability to global oceanic oxygen during the last deglaciation, but these reconstructions were limited to a single core from the Arabian Sea oxygen minimum zone, leaving uncertainties about the proxy’s broader spatial applicability. Here, we present a new sedimentary ε 205Tl record from ODP Site 1017E in the Southern California Margin oxygen minimum zone spanning the past 32 ka. The ε 205Tl record suggests that global oxygen content was lower during the Last Glacial Maximum (∼23–19 ka) relative to the Holocene, with oxygenation during the Heinrich Stadial 1 (∼18–14.7 ka) and the Younger Dryas (∼12.9–11.7 ka), and deoxygenation during the Bølling-Allerød (∼14.7–12.9 ka). These trends mirror ε 205Tl records from the Arabian Sea, reinforcing the robustness of Tl isotopes as a global ocean oxygen proxy. We further investigate how the Mn cycle modulates transient ε 205Tl variability during the last deglaciation. The results show that short-lived changes in Mn oxide burial, driven by oxygen fluctuations, disrupt steady-state Tl cycling and produce millennial-scale ε 205Tl variations. By connecting the Mn and Tl cycle, we present a semi-quantitative model of mean oceanic oxygen content over the last deglaciation highlighting the potential of ε 205Tl as a paleo-oxygen proxy. However, an improved understanding of the marine Mn budget and its response to glacial-interglacial cycles is required before true quantitative reconstructions of average ocean oxygen contents with Tl isotopes are possible
{"title":"Sedimentary thallium isotopes as a proxy for reconstructing global oceanic oxygenation during millennial-scale events","authors":"Fang Qian, Yi Wang, Kassandra M. Costa, Sune G. Nielsen","doi":"10.1016/j.gca.2025.12.049","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.049","url":null,"abstract":"The thallium isotopic composition (ε <ce:sup loc=\"post\">205</ce:sup>Tl) of seawater is a promising proxy for global oceanic redox conditions due to its strong association with manganese oxide burial. Previous studies have linked ε<ce:sup loc=\"post\">205</ce:sup>Tl variability to global oceanic oxygen during the last deglaciation, but these reconstructions were limited to a single core from the Arabian Sea oxygen minimum zone, leaving uncertainties about the proxy’s broader spatial applicability. Here, we present a new sedimentary ε <ce:sup loc=\"post\">205</ce:sup>Tl record from ODP Site 1017E in the Southern California Margin oxygen minimum zone spanning the past 32 ka. The ε <ce:sup loc=\"post\">205</ce:sup>Tl record suggests that global oxygen content was lower during the Last Glacial Maximum (∼23–19 ka) relative to the Holocene, with oxygenation during the Heinrich Stadial 1 (∼18–14.7 ka) and the Younger Dryas (∼12.9–11.7 ka), and deoxygenation during the Bølling-Allerød (∼14.7–12.9 ka). These trends mirror ε <ce:sup loc=\"post\">205</ce:sup>Tl records from the Arabian Sea, reinforcing the robustness of Tl isotopes as a global ocean oxygen proxy. We further investigate how the Mn cycle modulates transient ε <ce:sup loc=\"post\">205</ce:sup>Tl variability during the last deglaciation. The results show that short-lived changes in Mn oxide burial, driven by oxygen fluctuations, disrupt steady-state Tl cycling and produce millennial-scale ε <ce:sup loc=\"post\">205</ce:sup>Tl variations. By connecting the Mn and Tl cycle, we present a semi-quantitative model of mean oceanic oxygen content over the last deglaciation highlighting the potential of ε <ce:sup loc=\"post\">205</ce:sup>Tl as a paleo-oxygen proxy. However, an improved understanding of the marine Mn budget and its response to glacial-interglacial cycles is required before true quantitative reconstructions of average ocean oxygen contents with Tl isotopes are possible","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"161 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813958","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 : 2025-12-22DOI: 10.1016/j.gca.2025.12.043
Chris T.L. Cheung , Brian Beaty , Kohen W. Bauer , Cody L. Colleps , Dan Asael , Sean A. Crowe , Noah J. Planavsky , Paul S. Savage , N. Ryan McKenzie
The influences of bedrock lithological composition on weathering fluxes, including dissolved lithium isotopes (δ7Lidiss), in rivers remain unclear. To assess this, we present new elemental, mineralogical, and lithium isotopic data from river localities in Hong Kong that drain either purely silicic volcanic or siliciclastic sedimentary bedrock that were sampled during both the wet (summer) and dry (winter) seasons. Our data show marked geochemical and mineralogical differences in relation to bedrock composition. The silicic volcanic-draining rivers exhibit δ7Lidiss values ranging from 8.6‰ to 20.9‰, elevated dissolved alkali metal concentrations, and relatively higher kaolinite abundances, whereas siliciclastic sedimentary-draining rivers yield δ7Lidiss values ranging from 3.2‰ to 8.6‰, higher dissolved alkaline-earth metal concentrations, and relatively greater illite abundances. Collectively, the volcanic-draining rivers have higher average δ7Lidiss of ∼12.5‰ and higher bedload kaolinite/illite average ratios of 2.4, compared to the siliciclastic sedimentary-draining bedrock rivers that yield average δ7Lidiss of 6.0‰ and kaolinite/illite of 0.5. Mechanistically, this could have been driven by the lower abundance of reactive minerals in the siliciclastic bedrock and/or a higher degree of fracturing in the volcanic rocks, which can both increase water–rock interaction times and secondary clay formation, driving higher δ7Lidiss values. Seasonal variations were also observed in the Li data, with higher Li concentrations and dissolved δ7Li values (up to 8.0‰ heavier) measured during the dry winter season. This is attributed to lower river discharges in the dry season, enabling longer residence times for clay formation, and higher riverine δ7Li values. Higher major, alkali, and alkaline-earth concentrations were also measured during the dry season, with Group 3, transition metals, and rare earth elements more concentrated in the wet season, reflecting the impact of elemental mobility. Overall, our study highlights the influence of both bedrock lithology and regional weather patterns on riverine geochemical signatures within the same tectono-climatic setting. These findings help enhance understanding of the Li cycle, wherein riverine δ7Li fluxes to the ocean reflect a combination of lithology, hydrology, and weathering regime, further refining the utility of lithium isotopes for assessing modern and ancient silicate weathering processes on Earth’s surface.
{"title":"Lithological influence on Li isotope fractionation during silicate weathering","authors":"Chris T.L. Cheung , Brian Beaty , Kohen W. Bauer , Cody L. Colleps , Dan Asael , Sean A. Crowe , Noah J. Planavsky , Paul S. Savage , N. Ryan McKenzie","doi":"10.1016/j.gca.2025.12.043","DOIUrl":"10.1016/j.gca.2025.12.043","url":null,"abstract":"<div><div>The influences of bedrock lithological composition on weathering fluxes, including dissolved lithium isotopes (δ<sup>7</sup>Li<sub>diss</sub>), in rivers remain unclear. To assess this, we present new elemental, mineralogical, and lithium isotopic data from river localities in Hong Kong that drain either purely silicic volcanic or siliciclastic sedimentary bedrock that were sampled during both the wet (summer) and dry (winter) seasons. Our data show marked geochemical and mineralogical differences in relation to bedrock composition. The silicic volcanic-draining rivers exhibit δ<sup>7</sup>Li<sub>diss</sub> values ranging from 8.6‰ to 20.9‰, elevated dissolved alkali metal concentrations, and relatively higher kaolinite abundances, whereas siliciclastic sedimentary-draining rivers yield δ<sup>7</sup>Li<sub>diss</sub> values ranging from 3.2‰ to 8.6‰, higher dissolved alkaline-earth metal concentrations, and relatively greater illite abundances. Collectively, the volcanic-draining rivers have higher average δ<sup>7</sup>Li<sub>diss</sub> of ∼12.5‰ and higher bedload kaolinite/illite average ratios of 2.4, compared to the siliciclastic sedimentary-draining bedrock rivers that yield average δ<sup>7</sup>Li<sub>diss</sub> of 6.0‰ and kaolinite/illite of 0.5. Mechanistically, this could have been driven by the lower abundance of reactive minerals in the siliciclastic bedrock and/or a higher degree of fracturing in the volcanic rocks, which can both increase water–rock interaction times and secondary clay formation, driving higher δ<sup>7</sup>Li<sub>diss</sub> values. Seasonal variations were also observed in the Li data, with higher Li concentrations and dissolved δ<sup>7</sup>Li values (up to 8.0‰ heavier) measured during the dry winter season. This is attributed to lower river discharges in the dry season, enabling longer residence times for clay formation, and higher riverine δ<sup>7</sup>Li values. Higher major, alkali, and alkaline-earth concentrations were also measured during the dry season, with Group 3, transition metals, and rare earth elements more concentrated in the wet season, reflecting the impact of elemental mobility. Overall, our study highlights the influence of both bedrock lithology and regional weather patterns on riverine geochemical signatures within the same tectono-climatic setting. These findings help enhance understanding of the Li cycle, wherein riverine δ<sup>7</sup>Li fluxes to the ocean reflect a combination of lithology, hydrology, and weathering regime, further refining the utility of lithium isotopes for assessing modern and ancient silicate weathering processes on Earth’s surface.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 217-235"},"PeriodicalIF":5.0,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813973","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}
Oxygen cycling is a fundamental biogeochemical process regulating redox transformations across Earth’s environments, with hydroxyl radicals (•OH) playing a central role as highly reactive oxidants. However, the conditions that govern oxygen atom transfer and preservation in the oxidation products remain poorly constrained. Clarifying these constraints is essential for interpreting oxygen isotope signals in redox-active systems, particularly those involving reactive oxygen species (ROS). Here, we experimentally quantify the oxygen atom exchange kinetics between •OH and H2O (kex ≈ 6.5–8.2 × 104 M−1 s−1), revealing a rapid, pH-independent process governed by water concentration rather than OH− activity. Exchange completes within 0.24 μs in pure water and slows to second scale as the relative humidity decreased to 1 %. Using H218O and representative •OH scavengers including 5,5-dimethyl-1-pyrroline N-oxide (DMPO), phenol and sulfite, we demonstrate that preservation of •OH-derived oxygen occurs only when the radical’s lifetime is shorter than the exchange timescale. This condition can be satisfied when the total first-order rate contribution from all scavengers (∑kox[Scavenger]) exceeds ∼4.10 × 108 s−1, typically requiring millimolar concentrations. Moreover, only unsaturated organic compounds and low-valent oxide gases can capture the oxygen from •OH. In water-rich systems, DMPO–OH retains the original •OH oxygen, whereas phenol–OH undergoes progressive exchange during post-reaction storage. These findings define a preservation window governed by reaction timescale, scavenger type, and concentration, under which •OH-derived oxygen can be stably retained in products. Extrapolation to natural environments suggests that such preservation is feasible under low water activity—such as in arid soils, aerosols, mineral surfaces, or Martian regolith—where exchange can be effectively suppressed and scavenger concentrations tend to be locally elevated. Our findings constrain the kinetic and environmental boundaries of oxygen preservation in •OH-based processes, providing a mechanistic basis for refining oxygen isotope tracing in redox transformations across both Earth and planetary settings.
{"title":"Constraining conditions for the preservation of oxygen atoms from hydroxyl radicals in the oxidation products","authors":"Yunsong Zheng , Peng Zhang , Xiuli Li , Songhu Yuan","doi":"10.1016/j.gca.2025.12.048","DOIUrl":"10.1016/j.gca.2025.12.048","url":null,"abstract":"<div><div>Oxygen cycling is a fundamental biogeochemical process regulating redox transformations across Earth’s environments, with hydroxyl radicals (•OH) playing a central role as highly reactive oxidants. However, the conditions that govern oxygen atom transfer and preservation in the oxidation products remain poorly constrained. Clarifying these constraints is essential for interpreting oxygen isotope signals in redox-active systems, particularly those involving reactive oxygen species (ROS). Here, we experimentally quantify the oxygen atom exchange kinetics between •OH and H<sub>2</sub>O (<em>k<sub>ex</sub></em> ≈ 6.5–8.2 × 10<sup>4</sup> M<sup>−1</sup> s<sup>−1</sup>), revealing a rapid, pH-independent process governed by water concentration rather than OH<sup>−</sup> activity. Exchange completes within 0.24 μs in pure water and slows to second scale as the relative humidity decreased to 1 %. Using H<sub>2</sub><sup>18</sup>O and representative •OH scavengers including 5,5-dimethyl-1-pyrroline N-oxide (DMPO), phenol and sulfite, we demonstrate that preservation of •OH-derived oxygen occurs only when the radical’s lifetime is shorter than the exchange timescale. This condition can be satisfied when the total first-order rate contribution from all scavengers (∑<em>k<sub>ox</sub></em>[Scavenger]) exceeds ∼4.10 × 10<sup>8</sup> s<sup>−1</sup>, typically requiring millimolar concentrations. Moreover, only unsaturated organic compounds and low-valent oxide gases can capture the oxygen from •OH. In water-rich systems, DMPO–OH retains the original •OH oxygen, whereas phenol–OH undergoes progressive exchange during post-reaction storage. These findings define a preservation window governed by reaction timescale, scavenger type, and concentration, under which •OH-derived oxygen can be stably retained in products. Extrapolation to natural environments suggests that such preservation is feasible under low water activity—such as in arid soils, aerosols, mineral surfaces, or Martian regolith—where exchange can be effectively suppressed and scavenger concentrations tend to be locally elevated. Our findings constrain the kinetic and environmental boundaries of oxygen preservation in •OH-based processes, providing a mechanistic basis for refining oxygen isotope tracing in redox transformations across both Earth and planetary settings.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"414 ","pages":"Pages 89-99"},"PeriodicalIF":5.0,"publicationDate":"2025-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145813972","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 : 2025-12-21DOI: 10.1016/j.gca.2025.12.046
Bennett J.K. Wilson , Kazuhide Nagashima , Thomas J. Barrett , Veronica E. Di Cecco , Kimberly T. Tait , Michael G. Daly
The Tarda meteorite is a recently recovered C2-ungrouped carbonaceous chondrite that preserves evidence of early Solar System aqueous alteration. Tarda was found to share reflectance spectra with P-type asteroids, possibly enabling these elusive asteroids to be studied in the laboratory for the first time. Furthermore, Tarda has been shown to share many petrological and isotopic affinities with Tagish Lake – a pristine C2-ungrouped chondrite that is widely considered to source a D-type asteroid. Thus Tarda, Tagish Lake, and their respective spectral classes are probably genetically related, and potentially source a shared parent body. Despite their similarities, however, Tagish Lake hosts different lithologies and carbonate species than Tarda, suggesting distinct aqueous alteration histories between the two meteorites. Here, we present in-situ oxygen, carbon, and 53Mn–53Cr isotopic analyses of dolomite and magnetite in Tarda using Secondary Ion Mass Spectrometry to (i) investigate the conditions associated with aqueous alteration on the early Tarda parent body, and to (ii) compare our findings with Tagish Lake to assess heterogeneous aqueous alteration of their unique and likely shared parent body. For dolomite, we found that δ13C ranged from 55.8 ‰ to 72.9 ‰, while δ18O ranged from 23.3 ‰ to 28.8 ‰ with an average Δ17O of 0.1 ± 1.6. Dolomite additionally contained widespread 53Cr excesses that, if interpreted to have chronological significance, corresponds to a live [(53Mn/55Mn)0] value of (. For magnetite, the δ18O values ranged from −5.5 ‰ to 5.8 ‰ with an average Δ17O of 2.4 ‰ ± 1.7. Oxygen isotope thermometry of a co-precipitating dolomite–magnetite pair indicates alteration temperatures of °C. Compared to carbonates in Tagish Lake, dolomite in Tarda exhibits systematically lower δ17O, δ18O, and Δ17O signatures, but similar δ13C signatures. Temporally, the carbonates in both meteorites have identical ages within uncertainty. We conclude that Tarda has experienced greater aqueous alteration than Tagish Lake, likely due to increased water–rock interaction and/or higher temperatures.
{"title":"Aqueous alteration in the C2-ung Tarda meteorite: in situ isotopic evidence from dolomite and magnetite","authors":"Bennett J.K. Wilson , Kazuhide Nagashima , Thomas J. Barrett , Veronica E. Di Cecco , Kimberly T. Tait , Michael G. Daly","doi":"10.1016/j.gca.2025.12.046","DOIUrl":"10.1016/j.gca.2025.12.046","url":null,"abstract":"<div><div>The Tarda meteorite is a recently recovered C2-ungrouped carbonaceous chondrite that preserves evidence of early Solar System aqueous alteration. Tarda was found to share reflectance spectra with P-type asteroids, possibly enabling these elusive asteroids to be studied in the laboratory for the first time. Furthermore, Tarda has been shown to share many petrological and isotopic affinities with Tagish Lake – a pristine C2-ungrouped chondrite that is widely considered to source a D-type asteroid. Thus Tarda, Tagish Lake, and their respective spectral classes are probably genetically related, and potentially source a shared parent body. Despite their similarities, however, Tagish Lake hosts different lithologies and carbonate species than Tarda, suggesting distinct aqueous alteration histories between the two meteorites. Here, we present in-situ oxygen, carbon, and <sup>53</sup>Mn–<sup>53</sup>Cr isotopic analyses of dolomite and magnetite in Tarda using Secondary Ion Mass Spectrometry to (i) investigate the conditions associated with aqueous alteration on the early Tarda parent body, and to (ii) compare our findings with Tagish Lake to assess heterogeneous aqueous alteration of their unique and likely shared parent body. For dolomite, we found that δ<sup>13</sup>C ranged from 55.8 ‰ to 72.9 ‰, while δ<sup>18</sup>O ranged from 23.3 ‰ to 28.8 ‰ with an average Δ<sup>17</sup>O of 0.1 ± 1.6. Dolomite additionally contained widespread <sup>53</sup>Cr excesses that, if interpreted to have chronological significance, corresponds to a live [(<sup>53</sup>Mn/<sup>55</sup>Mn)<sub>0</sub>] value of (<span><math><mrow><mrow><mn>3.08</mn><mo>±</mo><mspace></mspace><mn>0.52</mn><mo>)</mo><mo>×</mo></mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>6</mn></mrow></msup></mrow></math></span>. For magnetite, the δ<sup>18</sup>O values ranged from −5.5 ‰ to 5.8 ‰ with an average Δ<sup>17</sup>O of 2.4 ‰ ± 1.7. Oxygen isotope thermometry of a co-precipitating dolomite–magnetite pair indicates alteration temperatures of <span><math><mrow><msubsup><mn>87</mn><mrow><mo>-</mo><mn>24</mn></mrow><mrow><mo>+</mo><mn>28</mn></mrow></msubsup></mrow></math></span>°C. Compared to carbonates in Tagish Lake, dolomite in Tarda exhibits systematically lower δ<sup>17</sup>O, δ<sup>18</sup>O, and Δ<sup>17</sup>O signatures, but similar δ<sup>13</sup>C signatures. Temporally, the carbonates in both meteorites have identical ages within uncertainty. We conclude that Tarda has experienced greater aqueous alteration than Tagish Lake, likely due to increased water–rock interaction and/or higher temperatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 219-234"},"PeriodicalIF":5.0,"publicationDate":"2025-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796045","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.2025.12.042
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}
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