Geochimica et Cosmochimica Acta最新文献

{"title":"Stable and radiogenic strontium isotopes trace the composition and diagenetic alteration of remnant glacial seawater","authors":"Madison M. Wood, Clara L. Blättler, Ana Kolevica, Anton Eisenhauer, Adina Paytan","doi":"10.1016/j.gca.2024.10.028","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.028","url":null,"abstract":"A remnant of glacial seawater preserved in the pore fluids of sediment cores from the Maldives Inner Sea provided an opportunity to investigate the stable strontium isotopic composition (<mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr) of the ocean during the Last Glacial Maximum and explore the usefulness of <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr as a tracer of early marine diagenesis. We used paired measurements of <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr and radiogenic Sr isotope ratios (<ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr) in pore fluids and surrounding carbonate sediments to constrain the diagenetic history of the preserved glacial water mass at IODP Sites U1466 and U1468. These pore fluid profiles document variability in <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr in a shallow marine setting, revealing distinct diagenetic processes dominating within different depth intervals. We find evidence for isotope fractionation during secondary calcite precipitation at intermediate depths and observe that in aragonite-dominated settings, fractionation during recrystallization may be obscured by the dissolution of aragonite in the uppermost sediments. Correcting for the effect of carbonate recrystallization on pore fluid Sr concentration ([Sr]) and isotopic composition, we estimate that glacial seawater [Sr] was higher (<mml:math altimg=\"si5.svg\" display=\"inline\"><mml:mrow><mml:mo>∼</mml:mo><mml:mn>98</mml:mn><mml:mspace width=\"1em\"></mml:mspace><mml:mi mathvariant=\"normal\">μ</mml:mi></mml:mrow></mml:math>M) and <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr lower (<mml:math altimg=\"si7.svg\" display=\"inline\"><mml:mo>∼</mml:mo></mml:math>0.32‰) compared to the modern ocean, consistent with hypotheses attributing the present-day disequilibrium of the ocean Sr budget to glacial/interglacial changes in shelf carbonate weathering and burial. Our results provide evidence that the ocean [Sr] and <mml:math altimg=\"si13.svg\" display=\"inline\"><mml:msup><mml:mrow><mml:mi>δ</mml:mi></mml:mrow><mml:mrow><mml:mn>88</mml:mn><mml:mo>/</mml:mo><mml:mn>86</mml:mn></mml:mrow></mml:msup></mml:math>Sr are sensitive to carbon cycle changes on timescales much shorter than its residence time (<mml:m","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"57 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673701","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}

{"title":"One-pot synthesis of non-canonical ribonucleosides and their precursors from aldehydes and ammonia under prebiotic Earth conditions","authors":"Yuta Hirakawa, Hidenori Okamura, Fumi Nagatsugi, Takeshi Kakegawa, Yoshihiro Furukawa","doi":"10.1016/j.gca.2024.11.006","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.006","url":null,"abstract":"The formation of polymers that can hold gene information and work as catalysts is a crucial step for the origin of life. The discovery of catalytic RNA (i.e., ribozyme) supports the hypothesis that RNA might have served these functions at the early stage of life on the Earth. Given this, the spontaneous formation of RNA monomers (i.e., ribonucleotides) and their polymerization on Hadean Earth are essential steps for the origin of life. Previous experiments have investigated the chemical reactions that allow the formation of ribonucleotides and their components. These works have revealed the required molecules to form biological ribonucleotides (i.e., canonical ribonucleotides). Based on geochemical perspectives, abundantly available reactive molecules spontaneously react with each other to provide abundant products. Aldehydes and ammonia are reactive molecules assumed to have been present in considerable amounts on Hadean Earth. However, little is understood about whether or not nucleotides and their components were formed from these molecules under prebiotic conditions. We investigated the incubation products of alkaline aqueous solutions of aldehydes and ammonia. The product solution contained sugars (including ribose), various imidazole derivatives, and ribosyl imidazole (i.e., imidazole ribonucleoside). Ribosyl imidazole is formed via ribosyl amine, which reveals a new reaction pathway for prebiotic ribonucleoside synthesis. The imidazole ribonucleoside was then phosphorylated to imidazole ribonucleotide via a simple dry-down reaction with phosphate. Borate ion improved the reaction yields of these nucleosides and nucleotides. Because all the reactants were available on prebiotic Earth and the reactions progressed spontaneously, imidazole ribonucleotides could have accumulated in prebiotic environments. The experimental simplicity of the present reaction suggests that imidazoles were more abundant than canonical nucleobases on the prebiotic Earth. This further implies that prebiotic oligonucleotides contained imidazole bases in addition to the canonical nucleobases. The improvement of the reaction yields by borate indicates that borate-rich environments were conducive places for the formation and accumulation of non-canonical nucleosides and nucleotides. Such environments could have facilitated the formation of primordial ribonucleic acids on Hadean Earth.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"11 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673610","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}

{"title":"Colloids control the mobilization of released zinc- and cadmium- species in calcite-rich soils","authors":"Xinyang Li ,&nbsp;Jiawen Zhou ,&nbsp;Pengjie Hu ,&nbsp;Tong Zhou ,&nbsp;Zhu Li ,&nbsp;Yongming Luo ,&nbsp;Longhua Wu ,&nbsp;Michael Schindler","doi":"10.1016/j.gca.2024.11.003","DOIUrl":"10.1016/j.gca.2024.11.003","url":null,"abstract":"<div><div>Cadmium (Cd)-bearing sphalerite (SP, ZnS) and smithsonite (SM, ZnCO₃) particulate matter (PM) is deposited on soils near carbonate-hosted Zn ore deposits. Whether and how carbonate rocks such as limestone influence the mobility of Cd and Zn in soils is largely unknown. For this reason, we conducted a soil incubation experiment to investigate the chemical and mineralogical changes in soil–soil solution samples, including the occurrence of Cd- and Zn-bearing colloids and nanoparticles. Here the addition of calcite to SP- and SM-spiked soils promoted the formation of Cd- and Zn- bearing nanoparticles and colloids and thus significantly decreased the concentrations of Cd and Zn in soil solutions. Transmission electron microscope and extended X-ray absorption fluorescence spectroscopy showed that the addition of calcite resulted in the formation of Fe-OM-Ca colloids (OM = organic matter), sequestrating Cd and Zn. Furthermore, the release of Ca²⁺ during the dissolution of calcite promoted the aggregation of colloids and thus decreased the mobility of Cd- and Zn-bearing colloids in the soil column. The addition of calcite also decreased the amount of Cd and Zn released from the dissolution of SP and SM through the formation of calcite nano-layers armoring particles of the SP and SM phases. This study provides new insights into the environmental fate of particulate Cd and Zn in soils around carbonate-hosted Pb-Zn ore deposits. Specifically, it shows that the formation and aggregation of Cd- and Zn-bearing colloids decrease the mobility and bioavailability of both elements.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 12-27"},"PeriodicalIF":4.5,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662873","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}

{"title":"The effect of burning on the dissolution behaviour and silicon and oxygen isotope composition of phytolith silica","authors":"Andrea J. Prentice, Elizabeth A. Webb","doi":"10.1016/j.gca.2024.11.007","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.007","url":null,"abstract":"The &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;30&lt;/ce:sup&gt;Si and &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values of opal-A precipitated in plants (silica phytoliths) have been shown to be useful for paleoenvironmental reconstructions. Here, the effects of burning and partial dissolution of phytoliths on their isotopic compositions and dissolution behaviour were examined. Phytoliths were heated to 700 °C and then dissolution experiments were conducted in batch reactors under a range of pH (4–8) and temperature (4–19 °C) conditions. Heating caused a −2.6 ‰ shift in phytolith &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values. NMR results suggest that heating reduces the number of surface vicinal silanols, which likely results in the formation of strained Si&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;O&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Si bonds which incorporate oxygen from &lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O-depleted hydroxyl groups. During dissolution, the &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O of burned phytoliths increased by up to 3.5 ‰ (average 1.8 ‰) until 15–45 % saturation was reached, and then adsorption of silica on the surface of the solid began to reduce the &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O value of solid silica despite a net dissolution. The maximum increase in &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O during dissolution of burned phytoliths is 1.8 ‰ smaller than previously observed for unburned silica subjected to partial dissolution under the same conditions. Heating did not cause a significant change in &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;30&lt;/ce:sup&gt;Si values, and partial dissolution of burned phytoliths caused a slight increase in &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;30&lt;/ce:sup&gt;Si values that was smaller in magnitude than for unburned phytoliths. Dissolution of burned phytoliths progressed more slowly than dissolution of fresh phytoliths in low pH and temperature conditions, but was faster than the dissolution of fresh phytoliths when pH &gt; 6 and temperature = 19 °C. We propose that because fewer hydrolysis sites exist on the surface of burned phytoliths that the isolated silanols that remain after heating are difficult to deprotonate at low pH resulting in slower dissolution. However, at higher pH the breakage of strained Si&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;O&lt;ce:glyph name=\"sbnd\"&gt;&lt;/ce:glyph&gt;Si bonds in burned phytoliths may explain their higher dissolution rate relative to fresh phytoliths. We recommend caution in using the &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values of soil phytoliths in paleoclimate reconstructions as they can be altered during both heating and partial dissolution. For phytolith assemblages collected from archaeological hearths or grasslands prone to wildfires, the shift towards lower &lt;ce:italic&gt;δ&lt;/ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O values caused by heating would result in overestimations of temperature using ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"33 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673613","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}

{"title":"The non-carbonaceous nature of Earth’s late-stage accretion","authors":"K.R. Bermingham, H.A. Tornabene, R.J. Walker, L.V. Godfrey, B.S. Meyer, P. Piccoli, S.J. Mojzsis","doi":"10.1016/j.gca.2024.11.005","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.005","url":null,"abstract":"Constraining the origin of Earth’s building blocks requires knowledge of the chemical and isotopic characteristics of the source region(s) where these materials accreted. The siderophile elements Mo and Ru are well suited to investigating the mass-independent nucleosynthetic (i.e., “genetic”) signatures of material that contributed to the latter stages of Earth’s formation. Studies contrasting the Mo and Ru isotopic compositions of the bulk silicate Earth (BSE) to genetic signatures of meteorites, however, have reported conflicting estimates of the proportions of the non-carbonaceous type or NC (presumptive inner Solar System origin) and carbonaceous chondrite type or CC (presumptive outer Solar System origin) materials delivered to Earth during late-stage accretion (likely including the Moon-forming event and onwards). The present study reports new mass-independent isotopic data for Mo, which are presumed to reflect the composition of the BSE. A comparison of the new estimate for the BSE composition with new data for a select suite of NC iron meteorites is used to constrain the genetic characteristics of materials accreted to Earth during late-stage accretion. Results indicate that the final 10 to 20 wt% of Earth’s accretion was dominated by NC materials that were likely sourced from the inner Solar System, although the addition of minor proportions of CC materials, as has been suggested to occur during accretion of the final 0.5 to 1 wt% of Earth’s mass, remains possible. If this interpretation is correct, it brings estimates of the genetic signatures of Mo and Ru during the final 10 to 20 wt% of Earth accretion into concordance.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"63 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142718838","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}

{"title":"Hf–W isotope systematics of bulk chondrites: Implications for early Solar System evolution","authors":"Jan L. Hellmann ,&nbsp;Gerrit Budde ,&nbsp;Lori N. Willhite ,&nbsp;Richard J. Walker","doi":"10.1016/j.gca.2024.10.027","DOIUrl":"10.1016/j.gca.2024.10.027","url":null,"abstract":"<div><div>The short-lived ¹⁸²Hf–¹⁸²W system is widely used for constraining the chronology of the early Solar System, including the timing of the formation, thermal evolution, and differentiation of planetary bodies. Utilizing the full potential of the Hf–W system requires knowledge of the Hf/W ratio and W isotopic composition of primitive chondritic material. However, metal-silicate heterogeneity among chondritic samples can complicate accurately determining the Hf–W systematics of bulk chondrite parent bodies. Moreover, interpreting Hf–W data for chondrites may be complicated by potential nucleosynthetic W isotope anomalies. To this end, we report Hf/W ratios and W isotope compositions for bulk ordinary and enstatite chondrites, as well as the first such data for Rumuruti chondrites. We find that ordinary and Rumuruti chondrites show no resolvable nucleosynthetic anomalies, whereas resolved ε¹⁸³W (<em>i.e.</em>, 0.01% deviation in ¹⁸³W/¹⁸⁴W from terrestrial standard) excesses in individual enstatite chondrites suggest the presence of nucleosynthetic W isotope anomalies in bulk meteorite samples originating in the inner Solar System. These anomalies necessitate corrections when accurately quantifying radiogenic ¹⁸²W variations. Furthermore, several ordinary chondrites deviate in Hf/W ratios and W composition from the parent body compositions previously obtained from internal ¹⁸²Hf–¹⁸²W isochrons, indicating variations in the abundance of metal across different chondrite samples. Similarly, the Hf–W systematics of some enstatite chondrites also deviate from the parent body values, which can be attributed to the heterogeneous distribution of Hf carrier phases. The new observations highlight the challenges in obtaining Hf-W data that are representative of the chondrite parent bodies from individual chondrites, especially from metal-rich samples. By contrast, Rumuruti chondrites of variable petrologic types exhibit uniform Hf/W and ¹⁸²W/¹⁸⁴W ratios, suggesting that these samples are representative of their parent body. Whereas their Hf/W ratio is similar to that of carbonaceous chondrites, their W isotope composition is less radiogenic. This indicates that the Rumuruti precursor reservoir most likely had a significantly lower Hf/W ratio than the ratio measured in Rumuruti chondrites today. These findings underscore the importance of understanding the likely variations in Hf-W isotope systematics of iron meteorite parent bodies for accurately determining the timing of core formation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 38-52"},"PeriodicalIF":4.5,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748489","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}

{"title":"Petrogenesis of the unbrecciated pigeonite cumulate eucrite Northwest Africa 8326: Bridging the gap between eucrites and diogenites","authors":"Xiao-Wen Liu, Ai-Cheng Zhang, Li-Hui Chen, Lang Zhang, Xiao-Jun Wang, Jia Liu, Li-Ping Qin, Yu Liu, Qiu-Li Li, Xiao-Xiao Ling","doi":"10.1016/j.gca.2024.11.004","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.004","url":null,"abstract":"Understanding of the diversity and petrogenesis of achondrites is critical for deciphering magmatic processes and the early evolution of planets and asteroids. Here, we report the detailed petrologic, mineralogical, geochemical, and chronological features of the unbrecciated Vestan meteorite Northwest Africa (NWA) 8326. We found that NWA 8326 is composed of coarse-grained orthopyroxene (∼74 vol%), plagioclase (∼19 vol%), fine-grained augite (∼5 vol%), and many accessory minerals such as chromite, ilmenite, Fe-sulfide, silica phases, K-feldspar, Ca-phosphate phases, zircon, baddeleyite, rutile, and primary Si,Al,K-rich glass, differing from typical howardite-eucrite-diogenite meteorites. Based on textural feature and compositional calculation of pyroxene, we suggest that the coarse-grained orthopyroxene was inverted from primary pigeonite and NWA 8326 should be classified as a pigeonite cumulate eucrite. The oxygen and chromium isotope data (Δ<ce:sup loc=\"post\">17</ce:sup>O = − 0.254 ± 0.009 ‰; ε<ce:sup loc=\"post\">54</ce:sup>Cr = − 0.60 ± 0.06) support this classification. A few zircon aggregates are observed in NWA 8326 and the grains therein show a core-mantle zoned texture in cathodoluminescence (CL) images, with the cores being dark and Al-rich while the mantles being bright and Al-poor. We interpret that the CL-dark cores are xenocrystic zircon grains derived from eucrites, whose presence indicates that NWA 8326 should have formed through partial melting of the Vestan mantle, with assimilation of eucritic material. The presence of xenocrystic zircon and primary Si,Al,K-rich glass and the large compositional variation of plagioclase indicate that NWA 8326 is an unequilibrated cumulate eucrite and hence the zircon <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb age of 4559.2 ± 5.2 (2σ) Ma represents the crystallization of NWA 8326. Reconciling the cumulative texture with the presence of the chemically evolved glass, NWA 8326 would be excavated during the late stage of its crystallization and escaped the prevalent crustal thermal metamorphism of the eucrite parent body. The Mg isotopic composition of NWA 8326 is higher than most diogenites, which suggests that the parent magma of such a pigeonite cumulate eucrite was derived from a source region with heavier magnesium isotopic composition (μ<ce:sup loc=\"post\">25</ce:sup>Mg: −90 to − 96 ppm).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"46 1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673612","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}

{"title":"Solubility of NaCl in water vapor at 400–700 °C","authors":"Sigríður María Aðalsteinsdóttir, Guðmundur Sverrisson, Samuel Warren Scott, Erlend Straume, Adolph M. Bravo, Andri Stefánsson","doi":"10.1016/j.gca.2024.11.002","DOIUrl":"https://doi.org/10.1016/j.gca.2024.11.002","url":null,"abstract":"Water significantly impacts the chemical evolution of the Earth’s crust, affecting environments from volcanic settings to hydrothermal systems. These fluids transport elements essential for geological processes, such as metal ore deposit formation. At high temperatures, as water transitions from liquid to vapor, its molecular structure changes, drastically reducing its capacity to dissolve solids and solvate ions. Here, we report experimental results of halite (NaCl<ce:inf loc=\"post\">(s)</ce:inf>) solubility in water vapor at 400–700 °C and 30–300 bar using a novel U-tube flow-through reactor system. The results show that halite solubility is low (<ce:italic>x</ce:italic><ce:inf loc=\"post\">NaCl,tot</ce:inf> = 3.2 × 10<ce:sup loc=\"post\">−9</ce:sup> to 2.9 × 10<ce:sup loc=\"post\">−4</ce:sup> mol/mol) and increases with temperature and pressure, attributed to the dissolution of NaCl followed by its hydration according to the reaction:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"230 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673614","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}

{"title":"River mouths are hotspots for terrestrial organic carbon burial on the Sunda Shelf: Implications for tropical coastal carbon sequestration","authors":"Bingbing Wei ,&nbsp;Stephanie Kusch ,&nbsp;Junjie Wu ,&nbsp;Hasrizal Shaari ,&nbsp;Gesine Mollenhauer ,&nbsp;Guodong Jia","doi":"10.1016/j.gca.2024.10.037","DOIUrl":"10.1016/j.gca.2024.10.037","url":null,"abstract":"<div><div>Tropical small mountainous rivers (SMRs), characterized by extensive basin weathering, discharge high amounts of sediments and particulate terrestrial organic carbon (OC_terr) into the ocean. Burial of OC_terr in marine sediments is important for atmospheric CO₂ sequestration, yet its rate and efficiency remain not fully understood. Previous studies indicated generally low burial rates and burial efficiencies of OC_terr in tropical coastal ocean settings influenced by SMRs but lacked detailed insights into specific processes and quantitative estimates of burial efficiencies. This study investigated δ¹³C values of bulk OC (δ¹³C_OC) and OC_terr biomarker proxies (BIT, #rings_tetra, ΣIIIa/ΣIIa and %C₃₂ 1,15-diol indices) in river surface sediments on the Malay Peninsula and marine surface sediments on the adjacent Sunda Shelf to quantify sedimentary OC_terr contents, burial rates, and burial efficiencies along the river-estuary-ocean continuum. The substantial variation in δ¹³C_OC and OC_terr biomarker proxies between riverbed and shelf sediments revealed a strong decrease in fractional OC_terr contribution offshore and alongshore. Using a two-endmember mixing model based on δ¹³C_OC, we determined average OC_terr contents of 1.40, 0.80, and 0.05 wt% in riverbed, river-mouth, and shelf sediments, respectively. The low OC_terr contents in offshore sediments are attributed to physical mechanisms (such as local hydrodynamic regime and clay mineral flocculation) that affect sediment dispersal. This process leads to notably high burial rates of terrigenous sediment (11.5 ± 2.1 kg m⁻² yr⁻¹) and OC_terr (99.2 ± 29.0 g m⁻² yr⁻¹) at river mouths. In comparison, burial rates of OC_terr were significantly lower (0.1–0.5 g m⁻² yr⁻¹) offshore due to strong degradation of OC_terr, resulting in a lower overall OC_terr burial efficiency across the study area (18.2 %) compared to the global marginal sea average (21 %). These findings highlight the significance of carbon burial at the mouths of SMRs as CO₂ sinks, whereas degradation of OC_terr during offshore transport is a potentially large CO₂ source in the tropical coastal ocean.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 1-11"},"PeriodicalIF":4.5,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587054","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}

{"title":"Citation for the 2024 F. W. Clarke Award to Jihua Hao","authors":"Dimitri A. Sverjensky","doi":"10.1016/j.gca.2024.10.031","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.031","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"57 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673617","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}