Geochimica et Cosmochimica Acta最新文献

Biomarker 14C evidence for sources and recycling of pre-aged organic carbon in Arctic permafrost regions

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-08 DOI: 10.1016/j.gca.2025.02.010

Julie Lattaud , Timothy I. Eglinton , Negar Haghipour , Marcus Schiedung , Lisa Bröder

Permafrost thaw has the potential to release ancient particulate and dissolved organic matter that had been stored for thousands of years. Previous studies have shown that dissolved organic matter from permafrost is very labile and can be used by heterotrophic microbes close to the thaw area. However, it is unknown if ancient particulate organic matter can also be utilized. This study aims to investigate whether arctic microbial communities (bacteria and Archaea) incorporate ancient organic matter potentially released from thawing permafrost into their biomass. We compare and contrast the radiocarbon signatures of microbial lipids and higher plant biomarkers (representing terrestrial organic matter) from five soil profiles and seven deltaic lake sediment cores from the Mackenzie River drainage basin, Arctic Canada. In the surface soils, modern to post-modern short-chain fatty acids (SCFA) ages indicate in situ microbial production, with differential rates of organic carbon (OC) cycling depending on soil moisture. In contrast, SCFA in deeper soils display millennial ages, which likely represent the microbial necromass preserved through mineral association. In deltaic lakes that are disconnected from the river, generally old SCFA suggests the uptake of pre-aged OC by bacteria. In perennially connected lakes, pre-aged SCFA could originate from in situ microbial uptake of old OC or from the Mackenzie River. Higher plant-derived long-chain fatty acids (LCFA) present older radiocarbon ages, reflecting mineral stabilization during either pre-aging in soils (for high closure lakes) or riverine transport (for no and low closure lakes). Archaeal lipids are younger than SCFA and LCFA in high closure lakes, and older in low and no closure lakes, mirroring bulk radiocarbon signatures due to their heterotrophic production. These radiocarbon signatures of bacterial biomarker lipids may therefore reflect microbial incorporation of ancient OC (e.g., derived from permafrost thaw) or exceptional preservation (e.g., through mineral stabilization). Hence, even in relatively high OC environments such as arctic aquatic ecosystems, microbes can rely on ancient OC for their growth.

{"title":"Biomarker 14C evidence for sources and recycling of pre-aged organic carbon in Arctic permafrost regions","authors":"Julie Lattaud , Timothy I. Eglinton , Negar Haghipour , Marcus Schiedung , Lisa Bröder","doi":"10.1016/j.gca.2025.02.010","DOIUrl":"10.1016/j.gca.2025.02.010","url":null,"abstract":"<div><div>Permafrost thaw has the potential to release ancient particulate and dissolved organic matter that had been stored for thousands of years. Previous studies have shown that dissolved organic matter from permafrost is very labile and can be used by heterotrophic microbes close to the thaw area. However, it is unknown if ancient particulate organic matter can also be utilized. This study aims to investigate whether arctic microbial communities (bacteria and Archaea) incorporate ancient organic matter potentially released from thawing permafrost into their biomass. We compare and contrast the radiocarbon signatures of microbial lipids and higher plant biomarkers (representing terrestrial organic matter) from five soil profiles and seven deltaic lake sediment cores from the Mackenzie River drainage basin, Arctic Canada. In the surface soils, modern to post-modern short-chain fatty acids (SCFA) ages indicate <em>in situ</em> microbial production, with differential rates of organic carbon (OC) cycling depending on soil moisture. In contrast, SCFA in deeper soils display millennial ages, which likely represent the microbial necromass preserved through mineral association. In deltaic lakes that are disconnected from the river, generally old SCFA suggests the uptake of pre-aged OC by bacteria. In perennially connected lakes, pre-aged SCFA could originate from <em>in situ</em> microbial uptake of old OC or from the Mackenzie River. Higher plant-derived long-chain fatty acids (LCFA) present older radiocarbon ages, reflecting mineral stabilization during either pre-aging in soils (for high closure lakes) or riverine transport (for no and low closure lakes). Archaeal lipids are younger than SCFA and LCFA in high closure lakes, and older in low and no closure lakes, mirroring bulk radiocarbon signatures due to their heterotrophic production. These radiocarbon signatures of bacterial biomarker lipids may therefore reflect microbial incorporation of ancient OC (e.g., derived from permafrost thaw) or exceptional preservation (e.g., through mineral stabilization). Hence, even in relatively high OC environments such as arctic aquatic ecosystems, microbes can rely on ancient OC for their growth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 75-85"},"PeriodicalIF":4.5,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Effect of temperature on 2H/1H fractionation in semi-continuous cultures of a marine diatom, coccolithophore, and dinoflagellate

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-07 DOI: 10.1016/j.gca.2025.02.005

Jiawei Gao , Rong Bi , Julian P. Sachs , Hailong Zhang , Yunning Cao , Matthew D. Wolhowe , Weiguo Liu , Meixun Zhao

Temperature regulates the metabolic rate of organisms and, together with salinity, determines seawater density, a key driver of ocean circulation and heat transport. The hydrogen isotope composition (²H/¹H) of phytoplankton lipids has been shown to vary systematically with salinity and applied as a paleosalinity proxy in marine sediments. The influence of temperature on ²H/¹H ratios of lipids from different phytoplankton groups remains poorly constrained, especially when other growth parameters known to influence ²H/¹H fractionation are held constant, such as growth rate, irradiance, and salinity. We investigated ²H/¹H ratios responses of lipid biomarkers (fatty acids (FAs), sterols and alkenones) to temperature (12 ∼ 27 °C) in three marine phytoplankton taxa, the diatom Phaeodactylum tricornutum, the dinoflagellate Prorocentrum donghaiense, and the coccolithophorid Emiliania huxleyi using semi-continuous cultures. We show that ²H/¹H fractionation of FAs in the dinoflagellate decreased by 2.2 ± 0.3 ‰ °C^–1 (p < 0.05), while that of sterols in the dinoflagellate and fatty acid C_14:0 in the diatom increased by 2.3 ‰ °C^–1 and 1.9 ‰ °C^–1 (p < 0.05), respectively, as temperature increased. ²H/¹H fractionation of the three types of lipids in the coccolithophores did not vary systematically with temperature. The underlying mechanism by which temperature alters lipid ²H/¹H fractionation likely involves its effect on the proportions of photosynthetic and metabolic NADPH incorporated into lipids, NADPH residence time in the chloroplast, the contribution of extra-plastidic pyruvate to FA synthesis, and the proportion of mevalonic acid- versus methylerythritol phosphate-derived precursors in sterols.

{"title":"Effect of temperature on 2H/1H fractionation in semi-continuous cultures of a marine diatom, coccolithophore, and dinoflagellate","authors":"Jiawei Gao , Rong Bi , Julian P. Sachs , Hailong Zhang , Yunning Cao , Matthew D. Wolhowe , Weiguo Liu , Meixun Zhao","doi":"10.1016/j.gca.2025.02.005","DOIUrl":"10.1016/j.gca.2025.02.005","url":null,"abstract":"<div><div>Temperature regulates the metabolic rate of organisms and, together with salinity, determines seawater density, a key driver of ocean circulation and heat transport. The hydrogen isotope composition (<sup>2</sup>H/<sup>1</sup>H) of phytoplankton lipids has been shown to vary systematically with salinity and applied as a paleosalinity proxy in marine sediments. The influence of temperature on <sup>2</sup>H/<sup>1</sup>H ratios of lipids from different phytoplankton groups remains poorly constrained, especially when other growth parameters known to influence <sup>2</sup>H/<sup>1</sup>H fractionation are held constant, such as growth rate, irradiance, and salinity. We investigated <sup>2</sup>H/<sup>1</sup>H ratios responses of lipid biomarkers (fatty acids (FAs), sterols and alkenones) to temperature (12 ∼ 27 °C) in three marine phytoplankton taxa, the diatom <em>Phaeodactylum tricornutum</em>, the dinoflagellate <em>Prorocentrum donghaiense</em>, and the coccolithophorid <em>Emiliania huxleyi</em> using semi-continuous cultures. We show that <sup>2</sup>H/<sup>1</sup>H fractionation of FAs in the dinoflagellate decreased by 2.2 ± 0.3 ‰ °C<sup>–1</sup> (<em>p</em> < 0.05), while that of sterols in the dinoflagellate and fatty acid C<sub>14:0</sub> in the diatom increased by 2.3 ‰ °C<sup>–1</sup> and 1.9 ‰ °C<sup>–1</sup> (<em>p</em> < 0.05), respectively, as temperature increased. <sup>2</sup>H/<sup>1</sup>H fractionation of the three types of lipids in the coccolithophores did not vary systematically with temperature. The underlying mechanism by which temperature alters lipid <sup>2</sup>H/<sup>1</sup>H fractionation likely involves its effect on the proportions of photosynthetic and metabolic NADPH incorporated into lipids, NADPH residence time in the chloroplast, the contribution of extra-plastidic pyruvate to FA synthesis, and the proportion of mevalonic acid- versus methylerythritol phosphate-derived precursors in sterols.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 86-97"},"PeriodicalIF":4.5,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143395209","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}

引用次数: 0

Moderately volatile elements in chondrites record chondrule formation, two-component mixing and redistribution on parent bodies

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-06 DOI: 10.1016/j.gca.2025.02.001

Ninja Braukmüller , Claudia Funk , Wafa Abouchami , Harvey Pickard , Mark Rehkämper , Alessandro Bragagni , Stephen J.G. Galer , Carsten Münker , Harry Becker , Frank Wombacher

Most chondrites are depleted in moderately volatile elements (MVE) relative to the bulk solar system composition represented by CI chondrites. Here we present high-precision isotope dilution data for 11 moderately volatile elements (S, Cu, Zn, Ga, Se, Ag, Cd, In, Sn, Te and Tl) together with Cd and Zn stable isotope compositions for carbonaceous, ordinary, enstatite and Rumuruti chondrites complemented by a literature compilation of MVE stable isotope compositions. Together these data allow new insights into the processes that led to MVE depletion in chondrites and their redistribution within parent bodies.

Moderately volatile element abundances in carbonaceous, ordinary and Rumuruti chondrites are best explained by two-component mixing between a chemically CI-like MVE-rich matrix and an MVE-poor refractory component dominated by chondrules. Chondrules are enriched in light MVE isotopes due to kinetic recondensation of a small vapor fraction initially lost from chondrules upon heating. Later, thermal metamorphism redistributed some MVE within chondrite parent bodies, which is evaluated here in a systematic way for different chondrite groups and plateau volatile elements based on related and comparatively large but unsystematic stable isotope fractionation. Compared to other chondrite classes, enstatite chondrites show less systematic MVE abundance patterns when the elements are plotted as a function of condensation temperatures. Type 3 and 4 enstatite chondrites are more MVE-rich than expected based on their low matrix fractions and are enriched in light Zn and Te isotopes relative to CI. The enrichment of light Zn and Te isotopes and high MVE abundances in type 3 and 4 enstatite chondrites relative to CI can be explained by recondensation of a larger MVE vapor fraction after chondrule formation than observed for other chondrite classes, which presumably occurred at comparatively high H₂ pressures. Because MVE abundances and isotope compositions are fully consistent with chondrule formation, two-component mixing and MVE redistribution on parent bodies, we refute partial condensation from a hot solar nebula as the cause for MVE depletion in chondrite formation regions of the protoplanetary disk.

{"title":"Moderately volatile elements in chondrites record chondrule formation, two-component mixing and redistribution on parent bodies","authors":"Ninja Braukmüller , Claudia Funk , Wafa Abouchami , Harvey Pickard , Mark Rehkämper , Alessandro Bragagni , Stephen J.G. Galer , Carsten Münker , Harry Becker , Frank Wombacher","doi":"10.1016/j.gca.2025.02.001","DOIUrl":"10.1016/j.gca.2025.02.001","url":null,"abstract":"<div><div>Most chondrites are depleted in moderately volatile elements (MVE) relative to the bulk solar system composition represented by CI chondrites. Here we present high-precision isotope dilution data for 11 moderately volatile elements (S, Cu, Zn, Ga, Se, Ag, Cd, In, Sn, Te and Tl) together with Cd and Zn stable isotope compositions for carbonaceous, ordinary, enstatite and Rumuruti chondrites complemented by a literature compilation of MVE stable isotope compositions. Together these data allow new insights into the processes that led to MVE depletion in chondrites and their redistribution within parent bodies.</div><div>Moderately volatile element abundances in carbonaceous, ordinary and Rumuruti chondrites are best explained by two-component mixing between a chemically CI-like MVE-rich matrix and an MVE-poor refractory component dominated by chondrules. Chondrules are enriched in light MVE isotopes due to kinetic recondensation of a small vapor fraction initially lost from chondrules upon heating. Later, thermal metamorphism redistributed some MVE within chondrite parent bodies, which is evaluated here in a systematic way for different chondrite groups and plateau volatile elements based on related and comparatively large but unsystematic stable isotope fractionation. Compared to other chondrite classes, enstatite chondrites show less systematic MVE abundance patterns when the elements are plotted as a function of condensation temperatures. Type 3 and 4 enstatite chondrites are more MVE-rich than expected based on their low matrix fractions and are enriched in light Zn and Te isotopes relative to CI. The enrichment of light Zn and Te isotopes and high MVE abundances in type 3 and 4 enstatite chondrites relative to CI can be explained by recondensation of a larger MVE vapor fraction after chondrule formation than observed for other chondrite classes, which presumably occurred at comparatively high H<sub>2</sub> pressures. Because MVE abundances and isotope compositions are fully consistent with chondrule formation, two-component mixing and MVE redistribution on parent bodies, we refute partial condensation from a hot solar nebula as the cause for MVE depletion in chondrite formation regions of the protoplanetary disk.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 43-62"},"PeriodicalIF":4.5,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143379268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Sources and fate of particulate organic matter along the river-estuary-coastal ocean continuum: Constraints from amino acid and amino sugar carbon isotopes

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-05 DOI: 10.1016/j.gca.2025.02.004

Jinqiang Guo , Eric P. Achterberg , Yuan Shen , Bu Zhou , Jinming Song , Xuegang Li , Liqin Duan , Huamao Yuan

Estuaries represent hotspots for organic matter cycling. Understanding the sources and fate of organic matter in estuaries is crucial for quantifying the transport of terrestrial organic carbon to the coastal ocean and air-sea carbon dioxide fluxes. Here we report the abundance and carbon isotopic signatures of bulk particulate organic matter (POM) as well as particulate amino sugars and amino acids in surface suspended particles along the salinity gradient in the Changjiang Estuary and adjacent coastal ocean. Our data show that bulk δ¹³C values are directly related to the δ¹³C values of essential amino acids, suggesting a control by primary production on bulk δ¹³C values. A large degree of fractionation (−26‰) between phytoplankton δ¹³C and dissolved inorganic carbon δ¹³C values was observed in regions with salinities greater than 28, leading to a decline in bulk δ¹³C values. Examining the δ¹³C patterns of individual amino sugars and amino acids reveals that terrestrial amino sugars are produced by mixed sources of bacteria, fungi, and algae, while terrestrial amino acids originate from vascular plants and bacteria. Along the salinity gradient, the source of amino sugars shifted to bacteria, whereas amino acids transitioned to algae. Moreover, the low carbon- and nitrogen-normalized yields of amino acids (∼10% and ∼22%, respectively) observed in the Changjiang River suggest an advanced diagenetic state of terrestrial POM. In contrast, elevated POM reactivity in moderate to high salinity zones indicates contributions from phytoplankton production. Using the bacterial biomarker muramic acid, we found that a substantial portion (∼19%) of terrestrial POM is of bacterial origin. Combining the distinct excursions in bulk, amino sugar, and amino acid δ¹³C values in low salinity (<20) regions of the estuary indicates that terrestrial organic matter is extensively removed in the estuarine regions. Together, these findings underscore significant alterations in the sources and properties of organic matter along the river-estuary-coastal ocean continuum, with bacterial reworking playing an important role.

{"title":"Sources and fate of particulate organic matter along the river-estuary-coastal ocean continuum: Constraints from amino acid and amino sugar carbon isotopes","authors":"Jinqiang Guo , Eric P. Achterberg , Yuan Shen , Bu Zhou , Jinming Song , Xuegang Li , Liqin Duan , Huamao Yuan","doi":"10.1016/j.gca.2025.02.004","DOIUrl":"10.1016/j.gca.2025.02.004","url":null,"abstract":"<div><div>Estuaries represent hotspots for organic matter cycling. Understanding the sources and fate of organic matter in estuaries is crucial for quantifying the transport of terrestrial organic carbon to the coastal ocean and air-sea carbon dioxide fluxes. Here we report the abundance and carbon isotopic signatures of bulk particulate organic matter (POM) as well as particulate amino sugars and amino acids in surface suspended particles along the salinity gradient in the Changjiang Estuary and adjacent coastal ocean. Our data show that bulk δ<sup>13</sup>C values are directly related to the δ<sup>13</sup>C values of essential amino acids, suggesting a control by primary production on bulk δ<sup>13</sup>C values. A large degree of fractionation (−26‰) between phytoplankton δ<sup>13</sup>C and dissolved inorganic carbon δ<sup>13</sup>C values was observed in regions with salinities greater than 28, leading to a decline in bulk δ<sup>13</sup>C values. Examining the δ<sup>13</sup>C patterns of individual amino sugars and amino acids reveals that terrestrial amino sugars are produced by mixed sources of bacteria, fungi, and algae, while terrestrial amino acids originate from vascular plants and bacteria. Along the salinity gradient, the source of amino sugars shifted to bacteria, whereas amino acids transitioned to algae. Moreover, the low carbon- and nitrogen-normalized yields of amino acids (∼10% and ∼22%, respectively) observed in the Changjiang River suggest an advanced diagenetic state of terrestrial POM. In contrast, elevated POM reactivity in moderate to high salinity zones indicates contributions from phytoplankton production. Using the bacterial biomarker muramic acid, we found that a substantial portion (∼19%) of terrestrial POM is of bacterial origin. Combining the distinct excursions in bulk, amino sugar, and amino acid δ<sup>13</sup>C values in low salinity (<20) regions of the estuary indicates that terrestrial organic matter is extensively removed in the estuarine regions. Together, these findings underscore significant alterations in the sources and properties of organic matter along the river-estuary-coastal ocean continuum, with bacterial reworking playing an important role.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 31-42"},"PeriodicalIF":4.5,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377826","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}

引用次数: 0

Soda lake phosphorus fluxes controlled by biological uptake imply abundant phosphate in plausible origin-of-life environments

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-04 DOI: 10.1016/j.gca.2025.01.040

Sebastian Haas , Benjamin M. Tutolo , David C. Catling

Phosphate is crucial for the origin of life but typical environmental concentrations are too low for prebiotic synthesis of essential biomolecules like nucleic acids. However, evaporative, sodium-carbonate rich “soda” lakes can accumulate extreme phosphate levels sufficient for prebiotic synthesis. In modern soda lakes, this presumably requires small biological and inorganic (apatite mineral formation) sinks, but the relative importance of these sinks is unclear because studies on phosphorus fluxes in soda lakes are lacking. Here, we quantified phosphorus source and sink fluxes in the extremely phosphate-rich Last Chance Lake (LCL), Canada, and neighboring, moderately phosphate-rich, Goodenough Lake (GL). Within the total phosphorus (0.1 wt%) in LCL sediments, sequential extraction showed 61 % detrital apatite, ∼19 % dissolved phosphate, ∼11 % organic-bound phosphorus (P_org), 6 % carbonate-bound P, and ∼2 % authigenic apatite. Combining these measurements with hydrological fluxes, we demonstrate that evapo-concentration of dilute inflow sufficed to accumulate tens of millimolar phosphate on a millennial timescale due to small sinks. Low apatite formation rates directly confirmed a previously hypothesized mechanism allowing extreme phosphate solubility at high carbonate concentrations. Yet, it is its 18 × lower P_org formation rates that mainly distinguish LCL from the less phosphate-rich, more biologically active GL. Because low productivity is key, evaporative soda lakes on prebiotic Earth should have commonly attained millimolar phosphate levels. Consequently, we identify soda lakes as the only known natural environments with sufficiently high phosphate levels for critical phosphorylation and catalysis in prebiotic synthesis.

{"title":"Soda lake phosphorus fluxes controlled by biological uptake imply abundant phosphate in plausible origin-of-life environments","authors":"Sebastian Haas , Benjamin M. Tutolo , David C. Catling","doi":"10.1016/j.gca.2025.01.040","DOIUrl":"10.1016/j.gca.2025.01.040","url":null,"abstract":"<div><div>Phosphate is crucial for the origin of life but typical environmental concentrations are too low for prebiotic synthesis of essential biomolecules like nucleic acids. However, evaporative, sodium-carbonate rich “soda” lakes can accumulate extreme phosphate levels sufficient for prebiotic synthesis. In modern soda lakes, this presumably requires small biological and inorganic (apatite mineral formation) sinks, but the relative importance of these sinks is unclear because studies on phosphorus fluxes in soda lakes are lacking. Here, we quantified phosphorus source and sink fluxes in the extremely phosphate-rich Last Chance Lake (LCL), Canada, and neighboring, moderately phosphate-rich, Goodenough Lake (GL). Within the total phosphorus (0.1 wt%) in LCL sediments, sequential extraction showed 61 % detrital apatite, ∼19 % dissolved phosphate, ∼11 % organic-bound phosphorus (P<sub>org</sub>), 6 % carbonate-bound P, and ∼2 % authigenic apatite. Combining these measurements with hydrological fluxes, we demonstrate that evapo-concentration of dilute inflow sufficed to accumulate tens of millimolar phosphate on a millennial timescale due to small sinks. Low apatite formation rates directly confirmed a previously hypothesized mechanism allowing extreme phosphate solubility at high carbonate concentrations. Yet, it is its 18 × lower P<sub>org</sub> formation rates that mainly distinguish LCL from the less phosphate-rich, more biologically active GL. Because low productivity is key, evaporative soda lakes on prebiotic Earth should have commonly attained millimolar phosphate levels. Consequently, we identify soda lakes as the only known natural environments with sufficiently high phosphate levels for critical phosphorylation and catalysis in prebiotic synthesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 63-74"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143388324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Temperature dominates leaf wax n-alkane carbon isotope composition of terrestrial C3 angiosperms in humid zones

IF 5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-04 DOI: 10.1016/j.gca.2025.01.045

Yuhang Wang, Zhengshun Liu, Mingming Zhang, Gaowen Dai, Xianyu Huang

The C3 plant leaf wax δ13C (δ13Calk) is commonly used to reconstruct past climates. However, our understanding of how precipitation and temperature influence terrestrial C3 δ13Calk is limited. To address this gap, we investigated the δ13C of n-C29 alkane (δ13C29) of C3 terrestrial angiosperms in subtropical humid regions in China and compiled a global dataset. Results show a strong correlation between C3 terrestrial angiosperms δ13C29 and mean annual temperature in both Chinese subtropical humid regions (r = −0.94, p < 0.001) and global humid zones (r = −0.78, p < 0.001). The linear fit lines of the regional and global datasets have similar slopes (−0.3129 vs −0.2896) and intercepts (−30.82 vs −31.41), indicating consistent responses to air temperature in global humid zones. When considering only sites with temperature data from meteorological stations, the correlation coefficient increases to −0.96 (p < 0.001) for the global dataset. In contrast to humid zones, mean annual precipitation significantly correlates with C3 terrestrial angiosperms δ13C29 in arid zones (r = −0.75, p < 0.001), supporting the main controls of precipitation in these areas. These findings emphasize the impact of temperature on C3 terrestrial δ13Calk, particularly in humid zones, and highlight caution when interpreting δ13Calk in geological records under changing hydroclimate conditions or unstable settings.

{"title":"Temperature dominates leaf wax n-alkane carbon isotope composition of terrestrial C3 angiosperms in humid zones","authors":"Yuhang Wang, Zhengshun Liu, Mingming Zhang, Gaowen Dai, Xianyu Huang","doi":"10.1016/j.gca.2025.01.045","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.045","url":null,"abstract":"The C<ce:inf loc=\"post\">3</ce:inf> plant leaf wax δ<ce:sup loc=\"post\">13</ce:sup>C (δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf>) is commonly used to reconstruct past climates. However, our understanding of how precipitation and temperature influence terrestrial C<ce:inf loc=\"post\">3</ce:inf> δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf> is limited. To address this gap, we investigated the δ<ce:sup loc=\"post\">13</ce:sup>C of <ce:italic>n</ce:italic>-C<ce:inf loc=\"post\">29</ce:inf> alkane (δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf>) of C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms in subtropical humid regions in China and compiled a global dataset. Results show a strong correlation between C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf> and mean annual temperature in both Chinese subtropical humid regions (r = −0.94, <ce:italic>p</ce:italic> < 0.001) and global humid zones (r = −0.78, <ce:italic>p</ce:italic> < 0.001). The linear fit lines of the regional and global datasets have similar slopes (−0.3129 vs −0.2896) and intercepts (−30.82 vs −31.41), indicating consistent responses to air temperature in global humid zones. When considering only sites with temperature data from meteorological stations, the correlation coefficient increases to −0.96 (<ce:italic>p</ce:italic> < 0.001) for the global dataset. In contrast to humid zones, mean annual precipitation significantly correlates with C<ce:inf loc=\"post\">3</ce:inf> terrestrial angiosperms δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">29</ce:inf> in arid zones (r = −0.75, <ce:italic>p</ce:italic> < 0.001), supporting the main controls of precipitation in these areas. These findings emphasize the impact of temperature on C<ce:inf loc=\"post\">3</ce:inf> terrestrial δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf>, particularly in humid zones, and highlight caution when interpreting δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alk</ce:inf> in geological records under changing hydroclimate conditions or unstable settings.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"10 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401583","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}

引用次数: 0

Monazite saturation in carbonatite melts at crustal and upper mantle conditions

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-04 DOI: 10.1016/j.gca.2025.01.039

Srijita Ray , Gregory M. Yaxley , Laura A. Miller , Andrew J. Berry

<div><div>Monazite (XPO<sub>4</sub> where X = light rare earth element) is one of the most important ore minerals for rare earth elements (REE) mined from carbonatites. This study explores the influence of pressure, temperature and melt composition on the solubility of monazite in carbonate melt using piston cylinder experiments. We aim to understand how such a highly soluble phosphate mineral may sometimes crystallise from carbonatite magma and form economic deposits of REE. Our findings reveal that the solubility of monazite in a sodic-dolomitic carbonate melt is high over the entire pressure (1.0–2.0 GPa), temperature (1000-1450˚C), and compositional space (Na<sub>2</sub>O-CaO-MgO-SiO<sub>2</sub>-F) of our study. It increases from ∼ 26 to ∼ 61 wt% CePO<sub>4</sub> equivalent over the temperature range of 1000–1450 °C at 2 GPa. However, the solubility product constant (lnK<sub>sp</sub>) decreases by approximately ∼ 23 % and 21 % equivalent with increasing melt SiO<sub>2</sub> (from 0 to ∼ 18 wt% melt SiO<sub>2</sub>) at 1275 °C and fluoride (from 0 to ∼ 5 wt% melt F<sup>-</sup>) concentrations at 1100 °C respectively. Variations in melt Ca# (atomic Ca/(Mg + Ca) = 0.2–1.0) and pressure (1.0–2.0 GPa) have negligible impacts on monazite solubility. We use the experimental data to formulate an empirical model relating the solubility product constant (K<sub>sp</sub>) of monazite in carbonate melt to temperature and melt compositional parameters:</div><div><span><math><msub><mi>lnK</mi><mi>sp</mi></msub><mo>=</mo><mi>ln</mi><mfenced><mrow><mfenced><msub><mrow><msub><mrow><mi>R</mi><mi>E</mi><mi>E</mi></mrow><mn>2</mn></msub><msub><mi>O</mi><mn>3</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></mfenced><mo>.</mo><mfenced><msub><mrow><msub><mi>P</mi><mn>2</mn></msub><msub><mi>O</mi><mn>5</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></mfenced></mrow></mfenced><mo>=</mo><mn>1.31</mn><mfenced><mn>0.50</mn></mfenced><mo>-</mo><mfrac><mrow><mn>8679</mn><mfenced><mn>733</mn></mfenced></mrow><mi>T</mi></mfrac><mo>-</mo><mn>3.35</mn><mrow><mo>(</mo><mn>0.34</mn><mo>)</mo></mrow><mo>×</mo><mfenced><msub><mi>SiO</mi><mn>2</mn></msub></mfenced><mo>-</mo><mn>1.68</mn><mrow><mo>(</mo><mn>0.34</mn><mo>)</mo></mrow><mo>×</mo><mfenced><mi>F</mi></mfenced></math></span></div><div>where [] represents the mole fractions of oxides in the melt of the rare earth elements, phosphorus and silicon, and fluoride, T is in Kelvin, and the parentheses indicate standard errors. <span><math><msub><mrow><msub><mrow><mi>R</mi><mi>E</mi><mi>E</mi></mrow><mn>2</mn></msub><msub><mi>O</mi><mn>3</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></math></span> represents the summation of the melt REE concentrations for those REE which are compatible in the experimentally synthesized monazite (La-Sm and Gd). These experimental results suggest that the formation of monazite requires relatively high co

{"title":"Monazite saturation in carbonatite melts at crustal and upper mantle conditions","authors":"Srijita Ray , Gregory M. Yaxley , Laura A. Miller , Andrew J. Berry","doi":"10.1016/j.gca.2025.01.039","DOIUrl":"10.1016/j.gca.2025.01.039","url":null,"abstract":"<div><div>Monazite (XPO<sub>4</sub> where X = light rare earth element) is one of the most important ore minerals for rare earth elements (REE) mined from carbonatites. This study explores the influence of pressure, temperature and melt composition on the solubility of monazite in carbonate melt using piston cylinder experiments. We aim to understand how such a highly soluble phosphate mineral may sometimes crystallise from carbonatite magma and form economic deposits of REE. Our findings reveal that the solubility of monazite in a sodic-dolomitic carbonate melt is high over the entire pressure (1.0–2.0 GPa), temperature (1000-1450˚C), and compositional space (Na<sub>2</sub>O-CaO-MgO-SiO<sub>2</sub>-F) of our study. It increases from ∼ 26 to ∼ 61 wt% CePO<sub>4</sub> equivalent over the temperature range of 1000–1450 °C at 2 GPa. However, the solubility product constant (lnK<sub>sp</sub>) decreases by approximately ∼ 23 % and 21 % equivalent with increasing melt SiO<sub>2</sub> (from 0 to ∼ 18 wt% melt SiO<sub>2</sub>) at 1275 °C and fluoride (from 0 to ∼ 5 wt% melt F<sup>-</sup>) concentrations at 1100 °C respectively. Variations in melt Ca# (atomic Ca/(Mg + Ca) = 0.2–1.0) and pressure (1.0–2.0 GPa) have negligible impacts on monazite solubility. We use the experimental data to formulate an empirical model relating the solubility product constant (K<sub>sp</sub>) of monazite in carbonate melt to temperature and melt compositional parameters:</div><div><span><math><msub><mi>lnK</mi><mi>sp</mi></msub><mo>=</mo><mi>ln</mi><mfenced><mrow><mfenced><msub><mrow><msub><mrow><mi>R</mi><mi>E</mi><mi>E</mi></mrow><mn>2</mn></msub><msub><mi>O</mi><mn>3</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></mfenced><mo>.</mo><mfenced><msub><mrow><msub><mi>P</mi><mn>2</mn></msub><msub><mi>O</mi><mn>5</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></mfenced></mrow></mfenced><mo>=</mo><mn>1.31</mn><mfenced><mn>0.50</mn></mfenced><mo>-</mo><mfrac><mrow><mn>8679</mn><mfenced><mn>733</mn></mfenced></mrow><mi>T</mi></mfrac><mo>-</mo><mn>3.35</mn><mrow><mo>(</mo><mn>0.34</mn><mo>)</mo></mrow><mo>×</mo><mfenced><msub><mi>SiO</mi><mn>2</mn></msub></mfenced><mo>-</mo><mn>1.68</mn><mrow><mo>(</mo><mn>0.34</mn><mo>)</mo></mrow><mo>×</mo><mfenced><mi>F</mi></mfenced></math></span></div><div>where [] represents the mole fractions of oxides in the melt of the rare earth elements, phosphorus and silicon, and fluoride, T is in Kelvin, and the parentheses indicate standard errors. <span><math><msub><mrow><msub><mrow><mi>R</mi><mi>E</mi><mi>E</mi></mrow><mn>2</mn></msub><msub><mi>O</mi><mn>3</mn></msub></mrow><mrow><mi>m</mi><mi>e</mi><mi>l</mi><mi>t</mi></mrow></msub></math></span> represents the summation of the melt REE concentrations for those REE which are compatible in the experimentally synthesized monazite (La-Sm and Gd). These experimental results suggest that the formation of monazite requires relatively high co","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Competitive incorporation of Ca, Sr, and Ba ions into amorphous carbonates

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-04 DOI: 10.1016/j.gca.2025.02.002

Zsombor Molnár , Máté Hegedűs , Péter Németh , Mihály Pósfai

Amorphous alkaline earth carbonates typically occur as metastable precursors of widespread crystalline phases. Despite their transient nature, the properties of the amorphous carbonates affect the attributes of the crystalline end-products. The lack of long-range ordering in the amorphous solids allows for the incorporation of various ions into their structures, resulting in a wider range of cation compositions than in crystalline carbonate phases, furnishing these solids with peculiar physico-chemical properties. Here, we studied abiotic factors that could control the degree of incorporation of Ca²⁺, Sr²⁺, and Ba²⁺ cations into amorphous carbonates, and focused on the effects that different cation compositions have on the lifetimes and structures of amorphous solids, as well as on the structures of their crystalline end-products. The partition coefficients (D_Ca, D_Sr, and D_Ba) between the solution and the solid decreased with increasing ionic radius; however, in ternary systems the incorporation of Ba²⁺ was favored over Sr²⁺. Electron diffraction patterns and pair distribution functions calculated from them showed that incorporated Sr²⁺ and Ba²⁺ cations significantly modified the structural properties of the amorphous carbonates (relative to amorphous calcium carbonate). The changes in short-range structure resulted in exceptional kinetic stability of the ternary mixed amorphous Ca–Sr–Ba carbonates, with the lifetime of Sr₀_.1Ba_.40Ca_.50C 65 times longer than that of amorphous calcium carbonate. Ba²⁺ enhanced the formation of calcite-type structures, even in the presence of Sr²⁺. These findings contribute to the understanding of both the incorporation of alkaline earth metals into amorphous carbonates and their roles in prolonging the lifetimes of amorphous solids; in addition, our results can be potentially used for technological applications.

{"title":"Competitive incorporation of Ca, Sr, and Ba ions into amorphous carbonates","authors":"Zsombor Molnár , Máté Hegedűs , Péter Németh , Mihály Pósfai","doi":"10.1016/j.gca.2025.02.002","DOIUrl":"10.1016/j.gca.2025.02.002","url":null,"abstract":"<div><div>Amorphous alkaline earth carbonates typically occur as metastable precursors of widespread crystalline phases. Despite their transient nature, the properties of the amorphous carbonates affect the attributes of the crystalline end-products. The lack of long-range ordering in the amorphous solids allows for the incorporation of various ions into their structures, resulting in a wider range of cation compositions than in crystalline carbonate phases, furnishing these solids with peculiar physico-chemical properties. Here, we studied abiotic factors that could control the degree of incorporation of Ca<sup>2+</sup>, Sr<sup>2+</sup>, and Ba<sup>2+</sup> cations into amorphous carbonates, and focused on the effects that different cation compositions have on the lifetimes and structures of amorphous solids, as well as on the structures of their crystalline end-products. The partition coefficients (D<sub>Ca</sub>, D<sub>Sr</sub>, and D<sub>Ba</sub>) between the solution and the solid decreased with increasing ionic radius; however, in ternary systems the incorporation of Ba<sup>2+</sup> was favored over Sr<sup>2+</sup>. Electron diffraction patterns and pair distribution functions calculated from them showed that incorporated Sr<sup>2+</sup> and Ba<sup>2+</sup> cations significantly modified the structural properties of the amorphous carbonates (relative to amorphous calcium carbonate). The changes in short-range structure resulted in exceptional kinetic stability of the ternary mixed amorphous Ca–Sr–Ba carbonates, with the lifetime of Sr<sub>0</sub><sub>.1</sub>Ba<sub>.40</sub>Ca<sub>.50</sub>C 65 times longer than that of amorphous calcium carbonate. Ba<sup>2+</sup> enhanced the formation of calcite-type structures, even in the presence of Sr<sup>2+</sup>. These findings contribute to the understanding of both the incorporation of alkaline earth metals into amorphous carbonates and their roles in prolonging the lifetimes of amorphous solids; in addition, our results can be potentially used for technological applications.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 18-30"},"PeriodicalIF":4.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Controls on the distribution of dissolved Cr in the upper water column of the Atlantic Basin 大西洋海盆上层水体溶解铬分布的控制因素

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-01 DOI: 10.1016/j.gca.2024.10.017

D. Gilliard , D.J. Janssen , N. Schuback , S.L. Jaccard

Over the last decades, the chromium (Cr) stable isotope system (referred to as δ⁵³Cr) has emerged as a proxy to reconstruct past oxygenation changes in Earth’s atmosphere and oceans. Although Cr is a promising paleoproxy, uncertainties remain as to the modern marine Cr cycle, and limited data are yet available in large swaths of the ocean, including the Atlantic Ocean. Here we present dissolved seawater Cr concentrations ([Cr]) and δ⁵³Cr along a meridional transect from the North to the South Atlantic (AMT 29). Chromium concentrations range from of 2.51 to 3.96 nmol kg⁻¹ (n = 68) and δ⁵³Cr values range from +0.86 ± 0.04 ‰ (2SEM) to +1.20 ± 0.02 ‰ (2SEM) (n = 68). In contrast to data from other ocean basins [Cr] and δ⁵³Cr show only a weak correlation (δ⁵³Cr vs. Ln([Cr]) R² = 0.17), inconsistent with a closed-system Rayleigh distillation model. These results can mainly be explained by horizontal advection and water mass mixing, which our data demonstrate are the dominant processes controlling [Cr] and δ⁵³Cr distributions throughout much of the Atlantic, while the impact of in situ biogeochemical cycling is comparatively minor. There is, indeed no clear impact of biological productivity nor of dysoxic environments in the (sub)tropical Atlantic on the cycling of Cr along the transect. This is likely explained by insufficiently depleted oxygen concentrations and relatively low biological productivity, resulting in these processes being of secondary importance relative to water mass mixing in shaping the distribution of Cr in the low- to mid-latitude Atlantic Ocean.

在过去的几十年里，铬（Cr）稳定同位素系统（称为 δ53Cr）已成为重建地球大气和海洋过去含氧量变化的替代物。尽管铬是一种很有前景的古代用指标，但现代海洋铬循环的不确定性依然存在，而且包括大西洋在内的大片海域的数据还很有限。在此，我们介绍了从北大西洋到南大西洋（AMT 29）经向横断面的海水溶解铬浓度（[Cr]）和δ53Cr。铬浓度范围为 2.51 至 3.96 nmol kg-1（n = 68），δ53Cr 值范围为 +0.86 ± 0.04 ‰（2SEM）至 +1.20 ± 0.02 ‰（2SEM）（n = 68）。与其它大洋盆地的数据相比，[Cr] 和 δ53Cr 只显示出微弱的相关性（δ53Cr vs. Ln([Cr]) R2 = 0.17），与封闭系统的瑞利蒸馏模型不一致。这些结果主要可以用水平平流和水团混合来解释，我们的数据表明，水平平流和水团混合是控制大西洋大部分地区[Cr]和δ53Cr 分布的主要过程，而原地生物地球化学循环的影响相对较小。事实上，（亚）热带大西洋的生物生产力或缺氧环境对横断面上的铬循环没有明显影响。这可能是由于氧气浓度不足和生物生产力相对较低，导致这些过程相对于水团混合在形成大西洋中低纬度地区铬的分布方面具有次要性。

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引用次数: 0

Fluid-mineral titanium isotope fractionation: Computational and empirical results with implications for mineral deposits 流体矿物钛同位素分馏：对矿床影响的计算和经验结果

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta

Pub Date : 2025-02-01 DOI: 10.1016/j.gca.2024.12.007

Christopher Emproto , Ryan Mathur , Mingguang Sun , Adam C. Simon , Linda Godfrey

Titanium (Ti) typically exhibits low mobility in geologic fluids due to the low aqueous solubility of common (Fe-)Ti oxide minerals. Consequently, Ti isotope variations (δ^49/47Ti, given as δ⁴⁹Ti) in geologic systems are primarily attributed to magmatic differentiation. Thus, the potential for fluid-mineral fractionation has received less attention. However, ligand-rich fluids are capable of mobilizing Ti as observed in natural systems and laboratory studies. As hydrothermal ore mineralization is commonly associated with ligand-rich brines capable of transporting significant quantities of metals, Ti isotopes may aid in understanding mineralization and alteration in complex hydrothermal systems. Here we present data from computational modeling of various Ti coordination complexes theorized to exist in geologic systems and/or under relevant experimental conditions as well as computed fractionation factors for various Ti-bearing crystalline phases to investigate the basic mechanics of equilibrium fluid-mineral Ti isotope fractionation. These results indicate that equilibrium fluid-mineral Ti isotope exchange between our modeled Ti complexes and phases with 6-coordinated Ti is predicted to generally lead to enrichment of heavy Ti isotopes in the fluid. Because minerals with 6-coordinated Ti (such as magnetite and ilmenite) are the most important reservoirs of Ti in the solid Earth, Ti isotope equilibration between terrestrial rocks and fluids can be generalized to enrich the fluid in heavy Ti isotopes. We also performed magnetite-ülvospinel leaching experiments to investigate fluid-mineral Ti isotope fractionation in this phase. Mineral leaching experiments varying acid strength, leaching temperature, and reaction time with HCl and HF qualitatively support the prediction that the fluid phase will become enriched in heavy Ti isotopes during fluid-mineral interactions that approach equilibrium with Ti-rich magnetite. Additionally, the leaching data also suggest that the fluid becomes slightly enriched in lighter Ti isotopes when Ti exchange is limited—potentially due to kinetic effects. Therefore, magnetite from natural systems may be depleted in heavy Ti isotopes during regenerative mineral replacement involving equilibration with fluids or may possibly become depleted in light Ti isotopes under a kinetic fractionation regime—leading to mineral δ⁴⁹Ti values that are insufficiently explained by magmatic differentiation or inter-mineral fractionation. These results are a first look at fluid-mineral interactions that may affect Ti isotope fractionation in hydrothermal mineral systems, and Ti isotopes should be further studied as a potential method of understanding aqueous metal transport and tracing alteration in mineral deposits.

钛（Ti）在地质流体中通常表现出低流动性，这是由于普通（Fe-）Ti氧化物矿物的水溶性较低。因此，地质系统中Ti同位素（δ49/47Ti，用δ49Ti表示）的变化主要归因于岩浆分异。因此，流体-矿物分选的潜力受到的关注较少。然而，在自然系统和实验室研究中观察到，富含配体的液体能够调动钛。由于热液矿化通常与能够运输大量金属的富配体盐水有关，因此Ti同位素可能有助于理解复杂热液系统中的矿化和蚀变。本文通过对地质系统和相关实验条件下理论存在的各种钛配位配合物的计算建模，以及各种含钛结晶相的计算分馏因子，研究平衡流体-矿物钛同位素分馏的基本机制。这些结果表明，我们的模型Ti配合物和具有6配位Ti的相之间的平衡流体-矿物Ti同位素交换通常会导致流体中重Ti同位素的富集。由于具有6配位Ti的矿物（如磁铁矿和钛铁矿）是固体地球中最重要的Ti储集层，因此可以推广陆相岩石与流体之间的Ti同位素平衡，使流体富集重Ti同位素。我们还进行了磁铁矿- 左尖晶石浸出实验，以研究这一阶段的流体矿物钛同位素分馏。不同酸强度、浸出温度和与HCl和HF反应时间的矿物浸出实验定性地支持了这样的预测：在流体-矿物相互作用过程中，流体相将富集重钛同位素，并与富钛磁铁矿接近平衡。此外，浸出数据还表明，当Ti交换受到限制时，流体中较轻的Ti同位素会略微富集，这可能是由于动力学效应。因此，来自自然系统的磁铁矿可能在与流体平衡的再生矿物替换过程中失去重钛同位素，或者可能在动力学分馏过程中失去轻钛同位素，导致矿物δ49Ti值不能充分解释岩浆分馏或矿物间分馏。这些结果是对热液矿物系统中可能影响钛同位素分馏的流体-矿物相互作用的第一次观察，Ti同位素应进一步研究，作为了解矿床水中金属运输和示踪蚀变的潜在方法。

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引用次数: 0