G. Pokrovski, C. Sanchez‐Valle, S. Guillot, A. Borisova, M. Muñoz, A. Auzende, O. Proux, J. Roux, J. Hazemann, D. Testemale, Y. Shvarov
Redox dynamics of subduction processes remain poorly constrained owing to the lack of direct geochemical tracers. We studied, using X-ray absorption spectroscopy, the chemical and redox state of arsenic in the Tso Morari serpentinites that are witnesses of the Himalayan subduction. Our measurements reveal remarkably contrasting redox speciation, from arsenide (As – III ) to arsenite (As III ) and arsenate (As V ). Combined with physical-chemical constraints, these data enable reconstruction of the ‘ redox travel ’ of arsenic in the subduction process. Upon early serpentinisation of mantle peridotite, arsenic was scavenged from the fluid and dragged down as insoluble nickel arsenide. Partial deserpentinisation close to the peak metamorphism (550 – 650 °C) resulted in oxidative dissolution of arsenide to aqueous As III and As V and their non-specific intake by antigorite. The As V /As III ratios ( ∼ 0.1 – 10) analysed in the mineral are ∼ 10 4 times higher on average than predicted assuming bulk system thermodynamic equilibrium. These findings reflect a transient out-of-equilibrium release of highly oxidised fluids, with f O 2 reaching ∼ 10 log units above the fayalite-magnetite-quartz buffer (FMQ þ 10). Arsenic in serpentinite is thus a sensitive record of subduction redox dynamics inaccessible when using traditional equilibrium approaches applied to bulk fluid-mineral systems.
{"title":"Redox dynamics of subduction revealed by arsenic in serpentinite","authors":"G. Pokrovski, C. Sanchez‐Valle, S. Guillot, A. Borisova, M. Muñoz, A. Auzende, O. Proux, J. Roux, J. Hazemann, D. Testemale, Y. Shvarov","doi":"10.7185/geochemlet.2225","DOIUrl":"https://doi.org/10.7185/geochemlet.2225","url":null,"abstract":"Redox dynamics of subduction processes remain poorly constrained owing to the lack of direct geochemical tracers. We studied, using X-ray absorption spectroscopy, the chemical and redox state of arsenic in the Tso Morari serpentinites that are witnesses of the Himalayan subduction. Our measurements reveal remarkably contrasting redox speciation, from arsenide (As – III ) to arsenite (As III ) and arsenate (As V ). Combined with physical-chemical constraints, these data enable reconstruction of the ‘ redox travel ’ of arsenic in the subduction process. Upon early serpentinisation of mantle peridotite, arsenic was scavenged from the fluid and dragged down as insoluble nickel arsenide. Partial deserpentinisation close to the peak metamorphism (550 – 650 °C) resulted in oxidative dissolution of arsenide to aqueous As III and As V and their non-specific intake by antigorite. The As V /As III ratios ( ∼ 0.1 – 10) analysed in the mineral are ∼ 10 4 times higher on average than predicted assuming bulk system thermodynamic equilibrium. These findings reflect a transient out-of-equilibrium release of highly oxidised fluids, with f O 2 reaching ∼ 10 log units above the fayalite-magnetite-quartz buffer (FMQ þ 10). Arsenic in serpentinite is thus a sensitive record of subduction redox dynamics inaccessible when using traditional equilibrium approaches applied to bulk fluid-mineral systems.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42925128","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 : 2022-07-01DOI: 10.7185/geochemlet.2222cor
X. Zhang, X. Peng
{"title":"Corrigendum to “How long for plastics to decompose in the deep sea?” by Zhang and Peng, 2022","authors":"X. Zhang, X. Peng","doi":"10.7185/geochemlet.2222cor","DOIUrl":"https://doi.org/10.7185/geochemlet.2222cor","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44658557","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}
G. Laukert, I. Peeken, D. Bauch, T. Krumpen, E. Hathorne, K. Werner, M. Gutjahr, M. Frank
https://doi.org/10.7185/geochemlet.2220 Radiogenic neodymium (Nd) isotopes (εNd) have the potential to serve as a geochemical tracer of the marine origin of Arctic sea ice. This capability results from pronounced εNd differences between the distinct marine and riverine sources, which feed the surface waters from which the ice forms. The first dissolved Nd isotope and rare earth element (REE) concentration data obtained from Arctic sea ice collected across the Fram Strait during RV Polarstern cruise PS85 in 2014 confirm the incorporation and preservation of the parental surface seawater εNd signatures despite efficient REE rejection. The large εNd variability between ice floes and within sea ice cores (−32 to −10) reflects changes in water mass distribution during ice growth and drift from the central Arctic Ocean to Fram Strait. In addition to the parental seawater composition, our new approach facilitates the reconstruction of the transfer of matter between the atmosphere, the sea ice and the ocean. In conjunction with satellite-derived drift trajectories, we enable a more accurate assessment of sea ice origin and spatiotemporal evolution, benefiting studies of sea ice biology, biodiversity, and biogeochemistry. Received 6 January 2022 | Accepted 5 May 2022 | Published 10 June 2022
{"title":"Neodymium isotopes trace marine provenance of Arctic sea ice","authors":"G. Laukert, I. Peeken, D. Bauch, T. Krumpen, E. Hathorne, K. Werner, M. Gutjahr, M. Frank","doi":"10.7185/geochemlet.2220","DOIUrl":"https://doi.org/10.7185/geochemlet.2220","url":null,"abstract":"https://doi.org/10.7185/geochemlet.2220 Radiogenic neodymium (Nd) isotopes (εNd) have the potential to serve as a geochemical tracer of the marine origin of Arctic sea ice. This capability results from pronounced εNd differences between the distinct marine and riverine sources, which feed the surface waters from which the ice forms. The first dissolved Nd isotope and rare earth element (REE) concentration data obtained from Arctic sea ice collected across the Fram Strait during RV Polarstern cruise PS85 in 2014 confirm the incorporation and preservation of the parental surface seawater εNd signatures despite efficient REE rejection. The large εNd variability between ice floes and within sea ice cores (−32 to −10) reflects changes in water mass distribution during ice growth and drift from the central Arctic Ocean to Fram Strait. In addition to the parental seawater composition, our new approach facilitates the reconstruction of the transfer of matter between the atmosphere, the sea ice and the ocean. In conjunction with satellite-derived drift trajectories, we enable a more accurate assessment of sea ice origin and spatiotemporal evolution, benefiting studies of sea ice biology, biodiversity, and biogeochemistry. Received 6 January 2022 | Accepted 5 May 2022 | Published 10 June 2022","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44448685","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}
X.‐M. Liu, R. Gaschnig, R. Rudnick, R. Hazen, A. Shahar
https://doi.org/10.7185/geochemlet.2221 The Fe isotopic composition of twenty four glacial diamictite composites with depositional ages ranging from theMesoarchean to the Palaeozoic serve as proxies of the average upper continental crust (UCC) and can be used to track how δ56Fe may have changed in the continental crust through time. The diamictites have elevated chemical index of alteration (CIA) values and other characteristics of weathered regoliths (e.g., strong depletion in soluble elements such as Sr), which they inherited from their upper crustal source regions. The δ56Fe values in the diamictite composites range from −0.59 ‰ to þ0.23 ‰. Excluding three samples impacted by the incorporation of materials from Fe formations, the diamictites have an average δ56Fe of 0.12 ± 0.13 ‰ (2σ), overlapping the recent estimated average δ56Fe of 0.09 ± 0.03 ‰ (2 s.d.) in the upper continental crust (Dauphas et al., 2017, and references therein). There is no obvious correlation between δ56Fe of the glacial diamictites and the CIA. Our data suggest that the Fe isotope composition of the upper continental crust has been relatively constant throughout Earth history and that chemical weathering is not important in producing Fe isotope variations in the upper continental crust. Pre-Great Oxidation Event (GOE) anoxic weathering, when iron was soluble in its divalent state, did not generate different Fe isotopic signatures from the post-GOE oxidative weathering environment in the upper continental crust. Therefore, the large Fe isotopic fractionations observed in various marine sedimentary records are likely due to processes occurring in the oceans (e.g., biological activity) rather than abiotic redox reactions on the continents. Received 4 March 2021 | Accepted 28 April 2022 | Published 10 June 2022
https://doi.org/10.7185/geochemlet.2221沉积年龄从中太古代到古生代的24种冰川杂岩复合物的Fe同位素组成是平均上大陆地壳（UCC）的代表，可用于跟踪δ56Fe在大陆地壳中随时间的变化。杂岩具有较高的化学蚀变指数（CIA）值和风化风化层的其他特征（例如，可溶性元素（如Sr）的强烈贫化），这些特征是从其上部地壳源区继承的。杂岩复合物中的δ56Fe值范围为-0.59‰至0.23‰。不包括三个受Fe地层物质结合影响的样品，杂岩的平均δ56Fe为0.12±0.13‰（2σ），与最近估计的上大陆地壳的平均δ56 Fe 0.09±0.03‰（2 s.d.）重叠（Dauphas et al.，2017，及其参考文献）。δ56Fe与CIA无明显相关性。我们的数据表明，在整个地球历史上，上大陆地壳的Fe同位素组成一直相对恒定，化学风化在上大陆地壳中产生Fe同位素变化并不重要。大氧化事件前缺氧风化，当铁以二价状态溶解时，在上部大陆地壳中，没有产生与大氧化事件后氧化风化环境不同的铁同位素特征。因此，在各种海洋沉积记录中观察到的大量铁同位素分馏可能是由于海洋中发生的过程（例如生物活动），而不是大陆上的非生物氧化还原反应。2021年3月4日收到| 2022年4月28日接受| 2022年6月10日发布
{"title":"Constant iron isotope composition of the upper continental crust over the past 3 Gyr","authors":"X.‐M. Liu, R. Gaschnig, R. Rudnick, R. Hazen, A. Shahar","doi":"10.7185/geochemlet.2221","DOIUrl":"https://doi.org/10.7185/geochemlet.2221","url":null,"abstract":"https://doi.org/10.7185/geochemlet.2221 The Fe isotopic composition of twenty four glacial diamictite composites with depositional ages ranging from theMesoarchean to the Palaeozoic serve as proxies of the average upper continental crust (UCC) and can be used to track how δ56Fe may have changed in the continental crust through time. The diamictites have elevated chemical index of alteration (CIA) values and other characteristics of weathered regoliths (e.g., strong depletion in soluble elements such as Sr), which they inherited from their upper crustal source regions. The δ56Fe values in the diamictite composites range from −0.59 ‰ to þ0.23 ‰. Excluding three samples impacted by the incorporation of materials from Fe formations, the diamictites have an average δ56Fe of 0.12 ± 0.13 ‰ (2σ), overlapping the recent estimated average δ56Fe of 0.09 ± 0.03 ‰ (2 s.d.) in the upper continental crust (Dauphas et al., 2017, and references therein). There is no obvious correlation between δ56Fe of the glacial diamictites and the CIA. Our data suggest that the Fe isotope composition of the upper continental crust has been relatively constant throughout Earth history and that chemical weathering is not important in producing Fe isotope variations in the upper continental crust. Pre-Great Oxidation Event (GOE) anoxic weathering, when iron was soluble in its divalent state, did not generate different Fe isotopic signatures from the post-GOE oxidative weathering environment in the upper continental crust. Therefore, the large Fe isotopic fractionations observed in various marine sedimentary records are likely due to processes occurring in the oceans (e.g., biological activity) rather than abiotic redox reactions on the continents. Received 4 March 2021 | Accepted 28 April 2022 | Published 10 June 2022","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42033429","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}
Rare earth elements (REEs) are powerful tools to track oceanic biogeochemical processes. However, our understanding of REE sources is incomplete, leading to contro-versial interpretations regarding their oceanic cycling. Continental margin sediments are often assumed to be a major source, but the sediment pore water data required to understand the processes controlling that potential source are scarce. Here, we mea-sure and compile pore water and estuarine REE data from the Changjiang (Yangtze) estuary – East China Sea shelf. We show that release of REEs, from shallow pore water to overlying seawater, is coupled to Mn reduction. In contrast, REEs are removed in deep pore water, perhaps via formation of an authigenic REE-bearing phase. This sedimentary source can potentially explain REE addition in the estuary at mid-high salinity. Our calculations suggest that the benthic flux is the largest Nd source ( ∼ 40 %) on the East China Sea shelf. Globally, however, despite a higher benthic Nd flux on the advection-dominated shelf, the much more extensive deep ocean still domi-nates the total area-integrated benthic flux. Our results call for a more extensive investigation of the magnitude of the benthic flux of REEs to the oceans.
{"title":"Dominance of benthic flux of REEs on continental shelves: implications for oceanic budgets","authors":"K. Deng, S. Yang, J. Du, E. Lian, D. Vance","doi":"10.7185/geochemlet.2223","DOIUrl":"https://doi.org/10.7185/geochemlet.2223","url":null,"abstract":"Rare earth elements (REEs) are powerful tools to track oceanic biogeochemical processes. However, our understanding of REE sources is incomplete, leading to contro-versial interpretations regarding their oceanic cycling. Continental margin sediments are often assumed to be a major source, but the sediment pore water data required to understand the processes controlling that potential source are scarce. Here, we mea-sure and compile pore water and estuarine REE data from the Changjiang (Yangtze) estuary – East China Sea shelf. We show that release of REEs, from shallow pore water to overlying seawater, is coupled to Mn reduction. In contrast, REEs are removed in deep pore water, perhaps via formation of an authigenic REE-bearing phase. This sedimentary source can potentially explain REE addition in the estuary at mid-high salinity. Our calculations suggest that the benthic flux is the largest Nd source ( ∼ 40 %) on the East China Sea shelf. Globally, however, despite a higher benthic Nd flux on the advection-dominated shelf, the much more extensive deep ocean still domi-nates the total area-integrated benthic flux. Our results call for a more extensive investigation of the magnitude of the benthic flux of REEs to the oceans.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47378416","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}
Q. Charbonnier, J. Bouchez, J. Gaillardet, É. Gayer, S. Porder
The role of biological cycling on the chemistry of rivers remains poorly understood. In an attempt to close this knowledge gap, here we examine the difference between the elemental supply to catchments through rock degradation and the corresponding elemental riverine export, for two non-nutrient elements lithium (Li) and sodium (Na) and two nutrients-like elements potassium (K) and barium (Ba), in 20 of the largest world river catchments. Overall, the riverine export of K and Ba are lower than their estimated release by catchment scale rock degradation, while the two fluxes match for Li and Na. Barium isotope constraints lending support to this observation, we take this difference between these two element groups as a suggestion of the influence of biological uptake of rock-derived nutrients on river chemistry. Nevertheless, the magnitude of riverine K depletion cannot be reconciled with a pervasive growth of the biota on continents, nor with an “ occult ” export of organic material that would go unnoticed by common sampling protocols. One plausible explanation for this conundrum could lie in thecomplex partitioning of elementsamongst soil, biota, and dead organic matter. As a consequence, our study emphasises the need for further work aiming at deciphering the cycle of rock-derived nutrients in the Critical Zone. catchmentscalemass budgets,for X = Na, Li(non-nutrients) and fornutrient/nutrient-likeelements( X = K and Ba). This approach aims to quantify the catchment scale (im)balance between the supply of a rock-derived nutrient X through rock degradation ( D X ) and the summed dissolved and solid riverine export ( W X and E X , respectively). The difference in the “ solubility ” translates into a difference in the size of the W X and E X arrows.
{"title":"A global imbalance in potassium and barium river export: the result of biological uptake?","authors":"Q. Charbonnier, J. Bouchez, J. Gaillardet, É. Gayer, S. Porder","doi":"10.7185/geochemlet.2214","DOIUrl":"https://doi.org/10.7185/geochemlet.2214","url":null,"abstract":"The role of biological cycling on the chemistry of rivers remains poorly understood. In an attempt to close this knowledge gap, here we examine the difference between the elemental supply to catchments through rock degradation and the corresponding elemental riverine export, for two non-nutrient elements lithium (Li) and sodium (Na) and two nutrients-like elements potassium (K) and barium (Ba), in 20 of the largest world river catchments. Overall, the riverine export of K and Ba are lower than their estimated release by catchment scale rock degradation, while the two fluxes match for Li and Na. Barium isotope constraints lending support to this observation, we take this difference between these two element groups as a suggestion of the influence of biological uptake of rock-derived nutrients on river chemistry. Nevertheless, the magnitude of riverine K depletion cannot be reconciled with a pervasive growth of the biota on continents, nor with an “ occult ” export of organic material that would go unnoticed by common sampling protocols. One plausible explanation for this conundrum could lie in thecomplex partitioning of elementsamongst soil, biota, and dead organic matter. As a consequence, our study emphasises the need for further work aiming at deciphering the cycle of rock-derived nutrients in the Critical Zone. catchmentscalemass budgets,for X = Na, Li(non-nutrients) and fornutrient/nutrient-likeelements( X = K and Ba). This approach aims to quantify the catchment scale (im)balance between the supply of a rock-derived nutrient X through rock degradation ( D X ) and the summed dissolved and solid riverine export ( W X and E X , respectively). The difference in the “ solubility ” translates into a difference in the size of the W X and E X arrows.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43658542","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}
Current Martian core composition models suggest an iron-rich core alloyed with 10 to 20 wt. % of sulfur. Although Mars is more oxidised than Earth, oxygen is usually discarded as a potential light element candidate, since its dissolution into iron is negligible at the pressures and temperatures prevailing during Mars ’ s primitive differentiation. However, it has recently been shown that oxygen interacts with the sulfur in the metal, which dramatically increases its solubility. Here, we investigated this novel process by carrying out metal-silicate equilibration experiments between 2 and 12 GPa, and 1673 and 2473 K, using piston-cylinder and multi-anvil presses. The experimental results show that oxygen was systematically incorporated in the metallic phase alongside sulfur, and a thermodynamic model was developed to para-metrise this interaction. The oxygen-sulfur interaction parameter arising from those thermodynamic equations was fitted and used in a multi-stage core modelling simulation. We found that a Martian core containing 14 to 19 wt. % S (maximum permissible concentration according to cosmochemical constraints) will also contain between 1.3 and 3.5 wt. % O. This would help to match the Martian core density estimate while being cosmochemically consistent. by High-pressure, high-temperature metal-silicate equilibration experiments were out on at The and on in was measured. Using thermodynamic modelling, we parametrised interaction from the experimental data and tested the robustness of the model to validate its predictive potential. We then applied our model to constrain the composition of the Martian core using multi-stage core formation modelling.
{"title":"Martian core composition from experimental high-pressure metal-silicate phase equilibria","authors":"H. Gendre, J. Badro, N. Wehr, S. Borensztajn","doi":"10.7185/geochemlet.2216","DOIUrl":"https://doi.org/10.7185/geochemlet.2216","url":null,"abstract":"Current Martian core composition models suggest an iron-rich core alloyed with 10 to 20 wt. % of sulfur. Although Mars is more oxidised than Earth, oxygen is usually discarded as a potential light element candidate, since its dissolution into iron is negligible at the pressures and temperatures prevailing during Mars ’ s primitive differentiation. However, it has recently been shown that oxygen interacts with the sulfur in the metal, which dramatically increases its solubility. Here, we investigated this novel process by carrying out metal-silicate equilibration experiments between 2 and 12 GPa, and 1673 and 2473 K, using piston-cylinder and multi-anvil presses. The experimental results show that oxygen was systematically incorporated in the metallic phase alongside sulfur, and a thermodynamic model was developed to para-metrise this interaction. The oxygen-sulfur interaction parameter arising from those thermodynamic equations was fitted and used in a multi-stage core modelling simulation. We found that a Martian core containing 14 to 19 wt. % S (maximum permissible concentration according to cosmochemical constraints) will also contain between 1.3 and 3.5 wt. % O. This would help to match the Martian core density estimate while being cosmochemically consistent. by High-pressure, high-temperature metal-silicate equilibration experiments were out on at The and on in was measured. Using thermodynamic modelling, we parametrised interaction from the experimental data and tested the robustness of the model to validate its predictive potential. We then applied our model to constrain the composition of the Martian core using multi-stage core formation modelling.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":"1 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41587532","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}
Recent theoretical calculations suggested that carbon and oxygen are important light elements in the Earth ’ s inner and outer core, respectively. We performed melting experiments on the Fe-C-O system and obtained ternary liquidus phase relations at ∼ 50, ∼ 136, and ∼ 200 GPa based on textural and compositional characterisations of recovered samples. Considering the previously reported Fe-C binary eutectic liquid composition, these results are extrapolated to 330 GPa, which constrains C and O concentrations in the liquid outer core that crystallises Fe at the inner core. Theory has predicted a possible range of the solid inner core composition in Fe-C-S-Si that explains seismological observations. The compositions of liquids Fe-C-O-S-Si in equilibrium with such solid Fe-C-S-Si alloys are calculated with the solid-liquid partition coefficient of C obtained in this study along with those of S and Si in the literature. These liquid compositions, however, do not satisfy constraints from both outer core observations and the liquidus phase relations examined in this study, suggesting that the inner core is not Fe-C-S-Si alloy but may include H as an important impurity element.
最近的理论计算表明，碳和氧分别是地球内核和外核中重要的轻元素。我们在Fe-C-O体系上进行了熔融实验，并根据回收样品的结构和成分特征，在~ 50、~ 136和~ 200 GPa下获得了三元液相关系。考虑到之前报道的铁-C二元共晶液体组成，这些结果被推断为330 GPa，这限制了液体外核中C和O的浓度，而内核中铁的结晶。理论预测了铁- c - s - si固体内核组成的可能范围，可以解释地震学观测。利用本研究得到的C的固液分配系数，结合文献中S和Si的固液分配系数，计算了Fe-C-O-S-Si与这种Fe-C-S-Si固体合金平衡态的液相组成。然而，这些液体成分不满足外核观测和本研究中检查的液相关系的约束，这表明内核不是Fe-C-S-Si合金，但可能包含H作为重要的杂质元素。
{"title":"Melting experiments on Fe-C-O to 200 GPa; liquidus phase constraints on core composition","authors":"F. Sakai, K. Hirose, K. Umemoto","doi":"10.7185/geochemlet.2218","DOIUrl":"https://doi.org/10.7185/geochemlet.2218","url":null,"abstract":"Recent theoretical calculations suggested that carbon and oxygen are important light elements in the Earth ’ s inner and outer core, respectively. We performed melting experiments on the Fe-C-O system and obtained ternary liquidus phase relations at ∼ 50, ∼ 136, and ∼ 200 GPa based on textural and compositional characterisations of recovered samples. Considering the previously reported Fe-C binary eutectic liquid composition, these results are extrapolated to 330 GPa, which constrains C and O concentrations in the liquid outer core that crystallises Fe at the inner core. Theory has predicted a possible range of the solid inner core composition in Fe-C-S-Si that explains seismological observations. The compositions of liquids Fe-C-O-S-Si in equilibrium with such solid Fe-C-S-Si alloys are calculated with the solid-liquid partition coefficient of C obtained in this study along with those of S and Si in the literature. These liquid compositions, however, do not satisfy constraints from both outer core observations and the liquidus phase relations examined in this study, suggesting that the inner core is not Fe-C-S-Si alloy but may include H as an important impurity element.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48801258","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}
Iron(III) reducing bacteria (IRB) are best known and most influential drivers for mobi-lising metal(loid)s via reductive dissolution of iron(III)-containing minerals. Our study challenges this preconception and found that IRB immobilise metal(loid)s by respiring elemental sulfur (S 0 ) even when Fe(III) reduction is prevailing under mildly acidic conditions. Antimony (Sb), a toxic contaminant, was chosen as an example of metal(loid)s. Antimonite-adsorbed goethite was incubated with Shewanella oneidensis MR-1, a widely distributed IRB, in the presence of S 0 at pH 6.5. The results show that although the extent of Fe(III) reduction ( > 100 μ mol) was over ten times greater than that of S 0 reduction ( < 8 μ mol), it was S 0 reduction that immobilised Sb through Sb 2 S 3 precipitation. Further, the thermodynamic calculation suggests that such great impacts of marginal S 0 reduction can be extended to other metal(loid)s via the formation of soluble thio-species or sulfide precipitates. This study redefines the role of IRB in the environmental fate of metal(loid)s, highlighting the strong impacts from the marginal S 0 reduction over the central Fe(III) reduction.
{"title":"Iron(III) reducing bacteria immobilise antimonite by respiring elemental sulfur","authors":"L. Ye, C. Jing","doi":"10.7185/geochemlet.2215","DOIUrl":"https://doi.org/10.7185/geochemlet.2215","url":null,"abstract":"Iron(III) reducing bacteria (IRB) are best known and most influential drivers for mobi-lising metal(loid)s via reductive dissolution of iron(III)-containing minerals. Our study challenges this preconception and found that IRB immobilise metal(loid)s by respiring elemental sulfur (S 0 ) even when Fe(III) reduction is prevailing under mildly acidic conditions. Antimony (Sb), a toxic contaminant, was chosen as an example of metal(loid)s. Antimonite-adsorbed goethite was incubated with Shewanella oneidensis MR-1, a widely distributed IRB, in the presence of S 0 at pH 6.5. The results show that although the extent of Fe(III) reduction ( > 100 μ mol) was over ten times greater than that of S 0 reduction ( < 8 μ mol), it was S 0 reduction that immobilised Sb through Sb 2 S 3 precipitation. Further, the thermodynamic calculation suggests that such great impacts of marginal S 0 reduction can be extended to other metal(loid)s via the formation of soluble thio-species or sulfide precipitates. This study redefines the role of IRB in the environmental fate of metal(loid)s, highlighting the strong impacts from the marginal S 0 reduction over the central Fe(III) reduction.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42279768","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}
C. Zurkowski, B. Lavina, S. Chariton, V. Prakapenka, A. Campbell
The Fe-FeS phase relations were explored in the 22 – 25 wt. % S compositional range using single crystal X-ray diffraction in a laser heated diamond anvil cell. At pressures up to 125 GPa and at high temperatures, Fe 2 S and Fe 12 S 7 were determined to co-crystallise. The novel Fe 12 S 7 compound adopts the Co 12 P 7 structure and Fe 2 S assumes the Fe 2 P-type structure. Applying these results to an Fe-FeS binary phase diagram exposes a complex series of FeS phase assemblages in the 16 – 25 wt. % S range, whereby minor changes in S content significantly affect the crystallisation sequence of Fe-S rich planetary cores. For core compositions S-rich of the Fe 2 S-Fe 12 S 7 eutectic, the small density difference between solid Fe 12 S 7 and Fe 2 S is likely to result in the formation of a core slush rather than a gravitationally stable inner core. Crystallisation of denser Fe 2 S at eutectic conditions could then result in gravitational settling of an Fe 2 S-rich inner core over time. As the Fe 2 P-type Fe 2 S has previously been identified forming at high temperatures to pressures as low as 22 GPa, the core crystallisation regimes determined here also elucidate that the Martian core sulfur composition must lie on the S-rich side of the Fe-Fe 3 S eutectic or even the S-rich side of the Fe 3 S-Fe 2 S eutectic to maintain a fully molten core.
{"title":"Stability of Fe2S and Fe12S7 to 125 GPa; implications for S-rich planetary cores","authors":"C. Zurkowski, B. Lavina, S. Chariton, V. Prakapenka, A. Campbell","doi":"10.7185/geochemlet.2217","DOIUrl":"https://doi.org/10.7185/geochemlet.2217","url":null,"abstract":"The Fe-FeS phase relations were explored in the 22 – 25 wt. % S compositional range using single crystal X-ray diffraction in a laser heated diamond anvil cell. At pressures up to 125 GPa and at high temperatures, Fe 2 S and Fe 12 S 7 were determined to co-crystallise. The novel Fe 12 S 7 compound adopts the Co 12 P 7 structure and Fe 2 S assumes the Fe 2 P-type structure. Applying these results to an Fe-FeS binary phase diagram exposes a complex series of FeS phase assemblages in the 16 – 25 wt. % S range, whereby minor changes in S content significantly affect the crystallisation sequence of Fe-S rich planetary cores. For core compositions S-rich of the Fe 2 S-Fe 12 S 7 eutectic, the small density difference between solid Fe 12 S 7 and Fe 2 S is likely to result in the formation of a core slush rather than a gravitationally stable inner core. Crystallisation of denser Fe 2 S at eutectic conditions could then result in gravitational settling of an Fe 2 S-rich inner core over time. As the Fe 2 P-type Fe 2 S has previously been identified forming at high temperatures to pressures as low as 22 GPa, the core crystallisation regimes determined here also elucidate that the Martian core sulfur composition must lie on the S-rich side of the Fe-Fe 3 S eutectic or even the S-rich side of the Fe 3 S-Fe 2 S eutectic to maintain a fully molten core.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41786676","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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