Geochimica et Cosmochimica Acta最新文献

{"title":"Thallium isotope cycling in a ferruginous Precambrian ocean analogue","authors":"Chadlin M. Ostrander ,&nbsp;Andy W. Heard ,&nbsp;Elizabeth D. Swanner ,&nbsp;Yunchao Shu ,&nbsp;Wang Zheng ,&nbsp;Yaqiu Zhao ,&nbsp;Sune G. Nielsen","doi":"10.1016/j.gca.2024.12.008","DOIUrl":"10.1016/j.gca.2024.12.008","url":null,"abstract":"<div><div>Precambrian oceans were overwhelmingly anoxic and rich in dissolved ferrous iron (Fe²⁺), conditions referred to as ‘ferruginous’. Yet, few paleoceanographic tools widely applied to the Precambrian sedimentary record are investigated in detail in the few available ferruginous settings today. We conducted a detailed thallium (Tl) isotope investigation of Deming Lake, a meromictic ferruginous lake in Itasca State Park (Minnesota, USA). Only slight changes were observed in dissolved Tl concentrations (Tl_diss) and isotopic compositions (ε²⁰⁵Tl_diss) between spring, summer, and winter months. This was despite the development of a winter ice cap, a dramatic shoaling of the oxycline, and large swings in dissolved and particulate Fe concentrations. Isotopic compositions of authigenic Tl (ε²⁰⁵Tl_A) leached from surface sediments across a shallow-to-deep gradient averaged –2.2 ± 0.9‱ (2SD) and were at all depths slightly lower than corresponding waters, which averaged 0.0 ± 1.3‱ (2SD). We estimate that the Tl isotope fractionation process responsible for driving this effect has an associated fractionation factor (α) of 0.9998 to 0.9999. Processes behind this fractionation could be preferential ²⁰³Tl removal by biomass and organic sulfur. Thallium removal from the uppermost water column during the spring and summer months had an associated α up to 1.0005, most likely due to the preferential sorption of ²⁰⁵Tl onto Mn oxide minerals. This process plays little to no role in setting sedimentary ε²⁰⁵Tl_A values, probably because Mn oxide minerals are unstable in sediments throughout the lake. We find no evidence of strongly coupled Tl and Fe cycling in Deming Lake, and by extension suspect that ferruginous conditions did not play an important direct role in ancient seawater Tl isotope mass-balance. What the lake does tell us, however, is that organic-rich and sulfur-poor sediments can slightly fractionate Tl isotopes. Ancient sediments formed under comparable conditions may be unreliable water column ε²⁰⁵Tl archives. And if these sediment types were widely distributed on the ancient seafloor, they could have exerted a minor effect on global seawater Tl isotope mass-balance. Our results provide novel insights into how Tl and its isotopes are cycled under ferruginous conditions, permitting more accurate application of the Tl isotope paleoredox proxy to the Precambrian sedimentary record.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 264-275"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142884586","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":"Building Earth with pebbles made of chondritic components","authors":"Susmita Garai,&nbsp;Peter L. Olson,&nbsp;Zachary D. Sharp","doi":"10.1016/j.gca.2024.11.021","DOIUrl":"10.1016/j.gca.2024.11.021","url":null,"abstract":"<div><div>Pebble accretion provides new insights into Earth’s building blocks and early protoplanetary disk conditions. Here, we show that mixtures of <em>chondritic components</em>: metal grains, chondrules, calcium-aluminum-rich inclusions (CAIs), and amoeboid olivine aggregates (AOAs) match Earth’s major element composition (Fe, Ni, Si, Mg, Ca, Al, O) within uncertainties, whereas no combination of chondrites and iron meteorites does. Our best fits also match the <em>ε</em>⁵⁴Cr and <em>ε</em>⁵⁰Ti values of Earth precisely, whereas the best fits for chondrites, or components with a high proportion of E chondrules, fails to match Earth. In contrast to some previous studies, our best-fitting component mixture is predominantly carbonaceous, rather than enstatite chondrules. It also includes 15 wt% of early-formed refractory inclusions (CAIs + AOAs), which is similar to that found in some C chondrites (CO, CV, CK), but notably higher than NC chondrites. High abundances of refractory materials is lacking in NC chondrites, because they formed after the majority of refractory grains were either drawn into the Sun or incorporated into terrestrial protoplanets via pebble accretion. We show that combinations of Stokes numbers of chondritic components build 0.35–0.7 Earth masses in 2 My in the Hill regime accretion, for a typical pebble column density of 1.2 kg/m² at 1 au. However, a larger or smaller column density leads to super-Earth or moon-mass bodies, respectively. Our calculations also demonstrate that a few My of pebble accretion with these components yields a total protoplanet mass inside 1 au exceeding the combined masses of Earth, Moon, Venus, and Mercury. Accordingly, we conclude that pebble accretion is a viable mechanism to build Earth and its major element composition from primitive chondritic components within the solar nebula lifetime.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 86-104"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095932","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":"Carbonate dissolution fluxes in deep-sea sediments as determined from in situ porewater profiles in a transect across the saturation horizon","authors":"Jaclyn E.P. Cetiner ,&nbsp;William M. Berelson ,&nbsp;Nick E. Rollins ,&nbsp;Xuewu Liu ,&nbsp;Frank J. Pavia ,&nbsp;Anna R. Waldeck ,&nbsp;Sijia Dong ,&nbsp;Kalla Fleger ,&nbsp;Holly A. Barnhart ,&nbsp;Matthew Quinan ,&nbsp;Rucha P. Wani ,&nbsp;Patrick A. Rafter ,&nbsp;Andrew D. Jacobson ,&nbsp;Robert H. Byrne ,&nbsp;Jess F. Adkins","doi":"10.1016/j.gca.2024.11.027","DOIUrl":"10.1016/j.gca.2024.11.027","url":null,"abstract":"<div><div>Despite their importance for long-term climate regulation, the rates and mechanisms of seafloor carbonate dissolution are poorly understood, especially with respect to calcite saturation and the role of sedimentary metabolic CO₂ production. Here, we present results from an in situ porewater sampler deployed at the Cocos Ridge in the eastern equatorial Pacific, where we examine seafloor carbonate dissolution in locations with bottom water Ω_calcite ranging from 1.0 to 0.84 (1600–3200 m). With cm-scale resolution from the sediment–water interface to 35 cm, we present porewater profiles of total alkalinity, pH, dissolved inorganic carbon (DIC), δ¹³C of DIC, Ω_calcite, [Mn], [Ca], and [Sr], as well as solid phase porosity, % CaCO₃, and % organic C. These profiles provide evidence that deep-sea sedimentary carbonate dissolution occurs via sediment-side control, wherein dissolution is dominated by sedimentary processes rather than strictly bottom water saturation state. We estimate dissolution fluxes using three independent approaches: alkalinity fluxes, δ¹³C of DIC combined with DIC fluxes, and [Ca] fluxes. We report seafloor dissolution fluxes with uncertainties &lt; 38 %: 40 ± 15, 98 ± 20, 100 ± 32, and 89 ± 27 μmol CaCO₃/m²/day at sites 3200, 2900, 2700, and 1600 m deep, respectively. The magnitude of dissolution fluxes is a function of bottom water saturation state (Ω_calcite), bottom water dissolved oxygen, and sedimentary CaCO₃ content, but not correlated with any of these parameters independently. We observe dissolution occurring at all stations, including where bottom water is saturated with respect to calcite, and present evidence that this occurs through respiration-driven dissolution within the sediment. At all sites, porewater Ω_calcite decreases below bottom water values before increasing toward saturation deeper in the sediment. Using the δ¹³C of DIC, we partition the DIC fluxes across the sediment–water interface and find 21–48 % of DIC is sourced from CaCO₃ dissolution, with the remainder sourced from organic matter respiration. We present a sedimentary mass balance, assembled with dissolution rates and mass accumulation rates obtained through Δ¹⁴C of foraminiferal calcite, and calculate CaCO₃ burial efficiencies between 2 and 67 %, inversely correlating with water depth. Our results also provide evidence that net chemical erosion of 5,000––10,000 year old carbonate is occurring at the deepest site. Aerobic organic C respiration coupled with sedimentary CaCO₃ dissolution, as documented here, will provide more alkalinity to bottom waters than from undersaturation-driven dissolution alone. This process can neutralize anthropogenic CO₂ at the seafloor in a larger range of saturation states than previously estimated.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 145-159"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095064","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":"Coupled feldspar dissolution and secondary mineral precipitation in batch systems: 6. Labradorite dissolution, calcite growth, and clay precipitation at 60 °C and pH 8.2–8.4","authors":"Mingkun Chen ,&nbsp;Lei Gong ,&nbsp;Jacques Schott ,&nbsp;Peng Lu ,&nbsp;Kaiyun Chen ,&nbsp;Honglin Yuan ,&nbsp;Jian Sun ,&nbsp;Si Athena Chen ,&nbsp;John Apps ,&nbsp;Chen Zhu","doi":"10.1016/j.gca.2024.11.030","DOIUrl":"10.1016/j.gca.2024.11.030","url":null,"abstract":"<div><div>We conducted experiments on concurrent labradorite dissolution, calcite precipitation, and clay precipitation in batch reactor systems and tracked reaction processes using multiple isotope tracers. Labradorite was chosen for its role as a major and reactive component in basalt; the experiments thus directly impact our understanding of CO₂ storage in basalt aquifers and enhanced rock weathering. We doped initial solutions with ²⁹Si, ⁴³Ca, and Ca¹³CO₃(s). Experiments were conducted at 60 °C and pH ∼ 8.3 for up to 840 h, with isotope ratios in the experimental aqueous solutions measured using MC-ICP-MS. Unidirectional rates of labradorite dissolution near equilibrium were approximately two orders of magnitude slower than far-from-equilibrium rates reported in the literature. Calcite growth occurred near equilibrium and the rates were limited by the labradorite dissolution rates.</div><div>In the steady state phase, the interplay of these three heterogeneous reactions—labradorite dissolution, calcite growth, and clay precipitation—results in a coupled system that approaches a near-equilibrium state. The system does not reach true equilibrium because labradorite continues to dissolve, albeit at a much slower rate near equilibrium. The overall reaction can be approximated as,</div><div>Na_0.4Ca_0.6Al_1.6Si_2.4O₈ + 0.6HCO₃^- + 1·.7H₂O + 0.4H⁺ → 0.4Na⁺ + 0.6CaCO_3(s) + 0.5Al₂Si₂O₅(OH)_4(s) + 0.6Al(OH)₄^- + 1.4SiO₂^o_(aq)</div><div>The experimental results show that using short-term far-from-equilibrium rate constants would lead to an overestimation of feldspar weathering rates at the Earth’s surface (e.g., basalt weathering and enhanced rock weathering) and CO₂ mineralization in basalt aquifers.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 181-198"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143095063","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":"Are scandium sulfate complexes effective in mobilizing scandium?","authors":"Jia-Xin Wang, A.E. Williams-Jones, Xue-Ni Zhang, Shun-Da Yuan","doi":"10.1016/j.gca.2025.01.038","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.038","url":null,"abstract":"Sulfate has been increasingly acknowledged as a key ligand for the mobilization and enrichment of rare earth elements (REEs). Here, we report the results of an investigation of the solubility of Sc<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>(s), scandium speciation, and the coordination geometry of scandium species in sulfate-bearing solutions using solubility experiments and <ce:italic>ab initio</ce:italic> molecular dynamics (AIMD) simulations. The investigation was conducted for temperatures of 175 to 250 °C at vapor-saturated water pressure. From the results of our experiments, we conclude that Sc(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> is the dominant scandium species, and that its formation constant (log <ce:italic>β<ce:inf loc=\"post\">1</ce:inf></ce:italic>) varies from 11.20 ± 0.08 at 175 °C to 14.21 ± 0.12 at 250 °C. The AIMD simulations show that the Sc(SO<ce:inf loc=\"post\">4</ce:inf>)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">−</ce:sup> complex is either doubly monodentate or has a mixed monodentate-bidentate configuration, and is coordinated with four water molecules. The species ScSO<ce:inf loc=\"post\">4</ce:inf> + was also identified in our experiments, but has a relatively low formation constant (log <ce:italic>β<ce:inf loc=\"post\">2</ce:inf></ce:italic>) varying from 7.24 ± 0.46 at 175 °C to 9.51 ± 3.50 at 250 °C. Modeling of the transport and deposition of scandium provides convincing evidence that sulfate scandium complexes can transport scandium efficiently in acidic fluids (pH below 4). Our simulations emphasize the critical roles played by fluid-rock interaction and fluid–fluid mixing in the genesis of scandium ores. This study presents the key thermodynamic data needed to evaluate scandium mobilization in sulfate-rich hydrothermal systems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"4 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401584","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":"Behaviour of bromine in Cl- and F-bearing alkali-rich felsic magmas at crustal depth: An experimental study at 800–1100 °C, 10–200 MPa","authors":"Carmela Federica Faranda,&nbsp;Gaëlle Prouteau,&nbsp;Bruno Scaillet,&nbsp;Joan Andújar","doi":"10.1016/j.gca.2024.11.024","DOIUrl":"10.1016/j.gca.2024.11.024","url":null,"abstract":"<div><div>Bromine, although a minor component in volcanic gases, has received increasing interest in recent studies due to its high atmospheric ozone depletion potential, but its behaviour in alkali-rich felsic hydrous magmas remains unexplored. In this study, fluid-melt partitioning experiments were carried out using natural, Cl- and F-bearing silicate glasses with phonolitic, comenditic and pantelleritic compositions. For each composition, experiments were performed with a range of Br concentrations, at <em>P-T</em> conditions simulating isothermal decompression degassing or isobaric equilibrium cooling at shallow crustal depth (800–1000 °C, 10–200 MPa, oxidising and reducing conditions). The major element, Cl and F concentrations of the run-product glasses were determined by electron microprobe and the Br concentrations by LA-ICPMS. Volatile concentrations in the fluid were determined by mass balance calculations. The experimental results show that more Br partitions into the fluid phase with increasing bulk halogen concentration. The most Br-doped experiments are typically saturated with a vapor phase and a hydrosaline liquid. Experiments at the lowest Br concentrations, closest to natural systems, show that the pressure dependence of vapor-melt Br partitioning is complex, with a minimum vapor-melt partition coefficient observed at 50 MPa in the phonolitic composition (1.8 ± 0.9 at 1000 °C and oxidising conditions). Our results indicate that the eruptive degassing of Br from peralkaline felsic magmas is restricted to the shallowest levels of the magmatic plumbing system and is likely to occur at much lower pressures than in metaluminous magmas. This observation is consistent with the composition of melt inclusions preserved in alkaline silicic magmas. An important finding is that the vapor-melt partitioning of Br and Cl decreases with increasing temperature. In phonolite, at 200 MPa and oxidising conditions, the Br vapor-melt partition coefficient decreases from 18.5 ± 3.6 at 900 °C to 3.8 ± 1.5 at 1000 °C. As the ratio between the Br and Cl vapor-melt partition coefficients is not conservative, the Br/Cl ratio in the vapor phase is likely to increase during isobaric cooling and degassing. The vapor-melt partition coefficients of Br and, to a lesser extent Cl also increase with decreasing <em>fO₂</em> in the phonolitic system, and the Br vapor-melt partition coefficient for a reduced alkaline magma is close to that for an oxidised calc-alkaline magma. Our results also show that during protracted storage at shallow levels, oxidised alkali- and F-rich rhyolites coexist with vapor and brine. This suggests that high F concentration promotes unmixing of the halogen-bearing phase coexisting with such melts. The exsolution of immiscible vapor and brine efficiently removes Br from peralkaline magmas and probably limits the flux of Br to the atmosphere from such magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 117-144"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142884588","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":"Source composition or melting effect: New evidence from Archean komatiites concerning the origin of low highly siderophile element abundances in Earth’s mantle","authors":"Xiaoyu Zhou ,&nbsp;Ratul Banerjee ,&nbsp;Laurie Reisberg ,&nbsp;Sisir K. Mondal","doi":"10.1016/j.gca.2024.12.004","DOIUrl":"10.1016/j.gca.2024.12.004","url":null,"abstract":"<div><div>Highly siderophile element (HSE) contents of komatiites have been widely used to estimate the HSE composition of Earth’s mantle. However, the interpretation of existing komatiite data is controversial, with some authors arguing that the Archean deep mantle komatiite source was impoverished in HSE due to slow admixture of a late accretion component, while others invoke a melting process that would allow observed komatiite abundances to be obtained from a mantle source with present-day HSE abundances. To obtain insight into this issue, we present new HSE abundance data for komatiites from the Gorumahishani greenstone belt of the Singhbhum Craton, eastern India. Our Sm-Nd and Re-Os isotope data indicate a ∼3.5 Ga age for these little-studied rocks, which provide extreme examples of Al-depleted and Ti-depleted komatiite varieties, juxtaposed over a short-length scale. The calculated parental melt compositions for the Al-depleted komatiites have 2.7 ± 0.2 ppb Ru, 3.4 ± 0.2 ppb Pt, and 3.2 ± 0.6 ppb Pd, whereas, for the Ti-depleted type these values are 4.4 ± 0.3 ppb Ru, 3.2 ± 0.6 ppb Pt, 3.0 ± 0.5 ppb Pd. These concentrations are similar to those found in most Archean komatiites at &gt;3.4 Ga. For the Al-depleted samples, these values would correspond to mantle abundances equivalent to ∼38 % of modern Bulk Silicate Earth (BSE) Ru contents and ∼24 and ∼21 % of BSE Pt and Pd contents, respectively, if it is assumed that simple extrapolation of the measured values to the MgO content of fertile peridotite provides an adequate approximation of the HSE composition of the BSE. To examine the alternative model that the low contents of Ru, Pd and Pt in Gorumahishani komatiites could be obtained from a mantle source with BSE-like HSE contents, we apply a simple two-stage critical melting model using current experimental HSE partitioning coefficients. The Ru abundances of the Gorumahishani Al-depleted komatiitic magmas can be produced from the pooled melts of a fertile source with BSE-like Ru and S contents during the first melting stage. The Ru abundances of the Ti-depleted komatiitic magmas can then be produced from remelting the residue left by this first melting stage. On the other hand, Pt and Pd abundances cannot be successfully modelled for either the Al-depleted or the Ti-depleted komatiites using available partition coefficients, though our current understanding of Pt and Pd partitioning after sulfide exhaustion is limited. The use of komatiites to characterize the abundance and distribution of HSE in the early mantle critically depends on developing a better understanding of the partitioning behaviors of these elements between mantle sources and komatiitic magmas.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"390 ","pages":"Pages 211-231"},"PeriodicalIF":4.5,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841535","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":"Constraining sulfur cycling in the Eastern Tibetan Plateau: Evidence for cryptic sulfur cycling and implications for the weathering budget","authors":"Jun Zhong, Albert Galy, Preston Cosslett Kemeny, Xuetao Zhu, Gilad Antler, Cong-Qiang Liu, Si-Liang Li","doi":"10.1016/j.gca.2025.01.041","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.041","url":null,"abstract":"The production of sulfuric acid (H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) through the oxidation of reduced sulfur removes alkalinity from the ocean–atmosphere system and increases atmospheric carbon dioxide concentration (&lt;ce:italic&gt;p&lt;/ce:italic&gt;CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;) over geologic timescales. In practice, quantifying CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; changes due to H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;-driven weathering requires deciphering the sources of sulfate (SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;) in river water. However, river SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; concentrations ([SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;]) or SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; sulfur and oxygen isotopic ratios (δ&lt;ce:sup loc=\"post\"&gt;34&lt;/ce:sup&gt;S&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; and δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt;) can potentially be modified after the initial weathering reactions, biasing the inversion calculations that underlie quantification for the impact of chemical weathering on &lt;ce:italic&gt;p&lt;/ce:italic&gt;CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;. Here, we identify such a non-conservative behavior with a new dataset of δ&lt;ce:sup loc=\"post\"&gt;34&lt;/ce:sup&gt;S&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt;, δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; in the Jinsha River and Yalong River draining the Eastern Tibetan Plateau is best explained by cryptic sulfur cycling in the catchments. As a result, measurements in δ&lt;ce:sup loc=\"post\"&gt;18&lt;/ce:sup&gt;O&lt;ce:inf loc=\"post\"&gt;SO4&lt;/ce:inf&gt; do not necessarily provide a simple tool for inferring SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; sources, especially in the dry season. The partition of major dissolved ions concentrations between their different sources by inversion suggests that the discharged-weighted mean [SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;]&lt;ce:inf loc=\"post\"&gt;sulfide oxidation&lt;/ce:inf&gt;/[SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt;] ratio is 0.47 and 0.78, corresponding to a yield for the oxidation of sulfide of 4.55 × 10&lt;ce:sup loc=\"post\"&gt;4&lt;/ce:sup&gt; and 6.05 × 10&lt;ce:sup loc=\"post\"&gt;4&lt;/ce:sup&gt; mol/km&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;/yr, for the Jinsha River and the Yalong River, respectively. The fraction of cations from carbonate weathering and the fraction of acid from sulfide oxidation obtained from river inversion show that chemical weathering for most samples is a CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; sink on short-term timescales but CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; source on long-term timescales. The year-long survey shows that sulfide weathering counteracts and surpasses all atmospheric CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; consumption by silicate weathering for the Yalong River and the Jinsha River, respectively. We attribute the enhanced role of H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;SO&lt;ce:inf loc=\"post\"&gt;4&lt;","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"225 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401585","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":"Experimental pathways of clay formation and kinetics of basalt alteration in poor drainage systems: Implications for weathering","authors":"Piyush Sriwastava, Vijay Kumar Saini, George Mathew, Anil D. Shukla","doi":"10.1016/j.gca.2025.01.042","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.042","url":null,"abstract":"Basalt being the most dominant rock on the earth’s crust, contributes significantly to the global elemental cycle through weathering. In recent years, the potential of basalt weathering has been continuously scrutinized as a carbon dioxide removal (CDR) strategy. An accurate estimation of such large-scale processes requires a deeper insight into the mechanism controlling the basalt glass dissolution under field conditions. This contribution assesses the chemical evolution of fluid interacting with basalt glass in poorly drained regimes. Experiments showed a drop in kinetics of alteration (r<ce:inf loc=\"post\">0</ce:inf> = 1.7 × 10<ce:sup loc=\"post\">-9</ce:sup> mol.m<ce:sup loc=\"post\">−2</ce:sup>. s<ce:sup loc=\"post\">−1</ce:sup>) by two orders of magnitude in 24 days and emphasizes the onset of secondary mineral formation within 20 hr of the start of dissolution. At first, Mg starts fractionating from the solution due to brucite oversaturation and reaches undersaturation after 60th hour due to onset of other Mg-bearing minerals. From the 54th hour, montmorillonite remains oversaturated until Mg is entirely consumed by precipitation at the 164th hour. SEM-EDS investigation shows the presence of two major morphologies of secondary products: (a) honeycomb shape (smectite), with high Mg (&gt;3 wt%) and octahedral composition similar [(Si/Al + Fe + Mg) and Al/Si] to smectite, (b) aggregate of ellipsoid and/or equant granular phases. Compositionally, elliptical and granular aggregates show affinity towards low Mg and high Fe variety of smectite amorphous precursor. The absence of pure brucite grains indicates epitaxial growth of Mg-rich, honeycomb-shaped phyllosilicate precursor on the brucite template due to well-reported structural similarity between the brucite layer and 2:1 phyllosilicate octahedral sheet. Elliptical and equant-shaped grains with or without compositional similarity with smectite phases have high Fe and low Mg, indicating their formation under a low Mg concentration stage in solution. Precipitation of the secondary phases at various stages of reaction progress affects the total reaction affinity in a closed system. Coupled dissolution and precipitation at the fluid-rock interface are responsible for lowering the kinetics of dissolution reactions in a closed system, previously explaining the slow kinetics of natural weathering regimes. The damped kinetics of dissolution and cations fractionation in secondary products within a few hours of onset of dissolution reaction can result in an overestimation (ten times) of CDR potential estimation by enhanced rock weathering (ERW) if calculations do not involve the nature of closed system evolution during basalt glass alteration.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401586","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":"Land-ocean connections in organic carbon cycling amid the Early Triassic (Smithian-Spathian) revealed through compound specific isotope analysis","authors":"Franziska R. Blattmann, Torsten W. Vennemann, Elke Schneebeli-Hermann, Hugo F.R. Bucher, Clayton R. Magill","doi":"10.1016/j.gca.2025.01.037","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.037","url":null,"abstract":"Following the largest mass extinction of the Phanerozoic, the Early Triassic was characterized by a series of carbon cycle perturbations as revealed through multiple global carbon isotope excursions (CIEs). The mechanistic drivers behind these perturbations are a subject of debate due to limited records that differentiate terrestrial and marine carbon cycling processes. In this study, we focus on the Smithian-Spathian boundary, which is characterized by a global positive CIE approximately 2<ce:hsp sp=\"0.25\"></ce:hsp>million years after the onset of the carbon cycle perturbations. We present the results of biomarker molecular distributions (i.e., <ce:italic>n</ce:italic>-alkanes) and compound-specific carbon isotope analyses (<ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf>) for organic matter extracted from shales deposited at the Stensiöfjellet section in Spitsbergen, Norway. The measured middle Smithian <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> values are among the lowest in the Phanerozoic and potentially indicate high atmospheric <ce:italic>p</ce:italic>CO<ce:inf loc=\"post\">2</ce:inf> and a low <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C value for CO<ce:inf loc=\"post\">2</ce:inf> as a result of the oxidation of organic carbon. Marine and terrestrial <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> records show parallel CIEs reflecting that both systems were equally affected by carbon cycle perturbations. Our data suggest the onset of the CIE started in the late middle Smithian, suggesting an earlier perturbation of the carbon cycle than previously recognized. Spathian <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">alkane</ce:inf> values remain elevated and diverge from bulk <ce:italic>δ</ce:italic><ce:sup loc=\"post\">13</ce:sup>C trends, reflecting an intrinsic shift in both the marine and terrestrial carbon cycle. Considered together, our compound-specific carbon isotope analyses foster useful insights into the multiple carbon cycle perturbations during an interval of extreme environmental conditions marked by continuous biological radiation and extinction pulses, which might even be analogous to imminent future anthropogenic changes in climate. This study further shows that compound specific carbon isotope analyses can potentially also disentangle deep-time carbon cycle perturbations.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"161 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401622","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}