{"title":"海水和海洋沉积物中河流颗粒的化学变化:对海水成分和大气CO2的影响","authors":"Klaus Wallmann, Sonja Geilert, Florian Scholz","doi":"10.2475/001c.87455","DOIUrl":null,"url":null,"abstract":"Numerous studies have shown that riverine particles react with seawater. Reactions include dissolution of reactive silicate minerals (e.g., feldspars) and formation of authigenic clays and carbonates. Previous studies have either focused on mineral dissolution (marine silicate weathering) or authigenic phase formation (reverse weathering). A comprehensive study that assesses all processes affecting the marine alteration of riverine particle has -to our knowledge- not yet been conducted. Our contribution aims to fill this gap. We first quantify cation exchange between seawater and riverine particles that occurs when particles enter the marine realm and show that significant global cation fluxes are induced by this process (-1.3 Tmol Na yr -1 , -0.2 Tmol K yr -1 , -0.4 Tmol Mg yr -1 , +1.2 Tmol Ca yr -1 ) where the positive sign indicates cation release into seawater while the negative sign denotes uptake on particles. We then use thermodynamic and kinetic modeling to investigate how much of the suspended particle load dissolves in contact with seawater and estimate corresponding global release rates for dissolved cations and silica assuming congruent dissolution (+0.06 Tmol Na yr -1 , +0.15 Tmol Ca yr -1 , +2.8 Tmol Si yr -1 ). Subsequently, we investigate rates of mineral dissolution and authigenic clay and carbonate formation in marine sediments applying reactive transport modeling, porewater data and mass balance calculations. Our best estimates for net fluxes across the sediment/water interface (dissolution–mineral formation) result as +1.5 Tmol Na yr -1 , -2.5 Tmol K yr -1 , -2.0 Tmol Mg yr -1 , +2.5 Tmol Ca yr -1 , and +1.9 Tmol Si yr -1 where most of the Na and Ca release is induced by plagioclase dissolution, K is taken up in authigenic clays and Mg is removed from solution by authigenic clay and carbonate formation. We conclude that the alkalinity of seawater is not significantly affected by marine silicate alteration since cation release fluxes (Na, Ca) are as high as cation uptake fluxes (K, Mg) on equivalent basis. Moreover, marine silicate weathering and reverse weathering are closely coupled since Al required for clay formation is mostly provided by feldspar dissolution while Al removal in authigenic clay promotes and maintains feldspar dissolution in marine sediments. Authigenic carbonate formation in anoxic subsurface sediments sequesters significant amounts of carbon (2.5 Tmol C yr -1 ) according to our estimates where most of the Ca and alkalinity required for carbonate formation are provided by the dissolution of Ca-bearing silicate minerals. This hidden sedimentary cycle provides a sink for dissolved inorganic carbon that may drive a slow draw-down of atmospheric CO 2 on geological timescales. Marine silicate alteration has an even stronger effect on the geochemical evolution of seawater by generating large fluxes of dissolved K, Mg, Ca and Si.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"12 1","pages":"0"},"PeriodicalIF":1.9000,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Chemical Alteration of Riverine Particles in Seawater and Marine Sediments: Effects on Seawater Composition and Atmospheric CO<sub>2</sub>\",\"authors\":\"Klaus Wallmann, Sonja Geilert, Florian Scholz\",\"doi\":\"10.2475/001c.87455\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Numerous studies have shown that riverine particles react with seawater. Reactions include dissolution of reactive silicate minerals (e.g., feldspars) and formation of authigenic clays and carbonates. Previous studies have either focused on mineral dissolution (marine silicate weathering) or authigenic phase formation (reverse weathering). A comprehensive study that assesses all processes affecting the marine alteration of riverine particle has -to our knowledge- not yet been conducted. Our contribution aims to fill this gap. We first quantify cation exchange between seawater and riverine particles that occurs when particles enter the marine realm and show that significant global cation fluxes are induced by this process (-1.3 Tmol Na yr -1 , -0.2 Tmol K yr -1 , -0.4 Tmol Mg yr -1 , +1.2 Tmol Ca yr -1 ) where the positive sign indicates cation release into seawater while the negative sign denotes uptake on particles. We then use thermodynamic and kinetic modeling to investigate how much of the suspended particle load dissolves in contact with seawater and estimate corresponding global release rates for dissolved cations and silica assuming congruent dissolution (+0.06 Tmol Na yr -1 , +0.15 Tmol Ca yr -1 , +2.8 Tmol Si yr -1 ). Subsequently, we investigate rates of mineral dissolution and authigenic clay and carbonate formation in marine sediments applying reactive transport modeling, porewater data and mass balance calculations. Our best estimates for net fluxes across the sediment/water interface (dissolution–mineral formation) result as +1.5 Tmol Na yr -1 , -2.5 Tmol K yr -1 , -2.0 Tmol Mg yr -1 , +2.5 Tmol Ca yr -1 , and +1.9 Tmol Si yr -1 where most of the Na and Ca release is induced by plagioclase dissolution, K is taken up in authigenic clays and Mg is removed from solution by authigenic clay and carbonate formation. We conclude that the alkalinity of seawater is not significantly affected by marine silicate alteration since cation release fluxes (Na, Ca) are as high as cation uptake fluxes (K, Mg) on equivalent basis. Moreover, marine silicate weathering and reverse weathering are closely coupled since Al required for clay formation is mostly provided by feldspar dissolution while Al removal in authigenic clay promotes and maintains feldspar dissolution in marine sediments. Authigenic carbonate formation in anoxic subsurface sediments sequesters significant amounts of carbon (2.5 Tmol C yr -1 ) according to our estimates where most of the Ca and alkalinity required for carbonate formation are provided by the dissolution of Ca-bearing silicate minerals. This hidden sedimentary cycle provides a sink for dissolved inorganic carbon that may drive a slow draw-down of atmospheric CO 2 on geological timescales. Marine silicate alteration has an even stronger effect on the geochemical evolution of seawater by generating large fluxes of dissolved K, Mg, Ca and Si.\",\"PeriodicalId\":7660,\"journal\":{\"name\":\"American Journal of Science\",\"volume\":\"12 1\",\"pages\":\"0\"},\"PeriodicalIF\":1.9000,\"publicationDate\":\"2023-09-19\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"American Journal of Science\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.2475/001c.87455\",\"RegionNum\":3,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q3\",\"JCRName\":\"GEOSCIENCES, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"American Journal of Science","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.2475/001c.87455","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
摘要
许多研究表明,河流颗粒与海水发生反应。反应包括活性硅酸盐矿物(如长石)的溶解和自生粘土和碳酸盐的形成。以往的研究要么集中在矿物溶解(海相硅酸盐风化),要么集中在自生相形成(逆风化)。据我们所知,尚未进行一项全面的研究,评估影响河流颗粒海洋变化的所有过程。我们的贡献旨在填补这一空白。我们首先量化了颗粒进入海洋领域时海水和河流颗粒之间发生的阳离子交换,并表明这一过程诱导了显著的全球阳离子通量(-1.3 Tmol Na yr -1, -0.2 Tmol K yr -1, -0.4 Tmol Mg yr -1, +1.2 Tmol Ca yr -1),其中正号表示阳离子释放到海水中,负号表示颗粒吸收。然后,我们使用热力学和动力学模型来研究悬浮颗粒负载在与海水接触时溶解了多少,并在假设完全溶解(+0.06 Tmol Na / yr -1, +0.15 Tmol Ca / yr -1, +2.8 Tmol Si / yr -1)的情况下估计溶解阳离子和二氧化硅的相应全球释放率。随后,我们利用反应输运模型、孔隙水数据和质量平衡计算,研究了海洋沉积物中矿物溶解和自生粘土和碳酸盐形成的速率。我们对沉积物/水界面(溶解-矿物形成)净通量的最佳估计结果为+1.5 Tmol Na / yr -1、-2.5 Tmol K / yr -1、-2.0 Tmol Mg / yr -1、+2.5 Tmol Ca / yr -1和+1.9 Tmol Si / yr -1,其中大部分Na和Ca释放是由斜长石溶解引起的,K被自生粘土吸收,Mg被自生粘土和碳酸盐形成从溶液中去除。我们得出结论,海水的碱度不受海洋硅酸盐蚀变的显著影响,因为阳离子释放通量(Na, Ca)与阳离子吸收通量(K, Mg)相当。此外,由于粘土形成所需的铝主要由长石溶蚀提供,而自生粘土中铝的去除促进并维持了海洋沉积物中长石的溶蚀,因此海相硅酸盐风化和逆风化是紧密耦合的。根据我们的估计,缺氧地下沉积物中自生碳酸盐的形成吸收了大量的碳(2.5 Tmol C / 1),其中碳酸盐形成所需的大部分钙和碱度是由含钙硅酸盐矿物的溶解提供的。这个隐藏的沉积旋回为溶解的无机碳提供了一个汇,它可能会在地质时间尺度上推动大气二氧化碳的缓慢减少。海相硅酸盐蚀变通过产生大量溶解的K、Mg、Ca和Si,对海水的地球化学演化具有更强的影响。
Chemical Alteration of Riverine Particles in Seawater and Marine Sediments: Effects on Seawater Composition and Atmospheric CO2
Numerous studies have shown that riverine particles react with seawater. Reactions include dissolution of reactive silicate minerals (e.g., feldspars) and formation of authigenic clays and carbonates. Previous studies have either focused on mineral dissolution (marine silicate weathering) or authigenic phase formation (reverse weathering). A comprehensive study that assesses all processes affecting the marine alteration of riverine particle has -to our knowledge- not yet been conducted. Our contribution aims to fill this gap. We first quantify cation exchange between seawater and riverine particles that occurs when particles enter the marine realm and show that significant global cation fluxes are induced by this process (-1.3 Tmol Na yr -1 , -0.2 Tmol K yr -1 , -0.4 Tmol Mg yr -1 , +1.2 Tmol Ca yr -1 ) where the positive sign indicates cation release into seawater while the negative sign denotes uptake on particles. We then use thermodynamic and kinetic modeling to investigate how much of the suspended particle load dissolves in contact with seawater and estimate corresponding global release rates for dissolved cations and silica assuming congruent dissolution (+0.06 Tmol Na yr -1 , +0.15 Tmol Ca yr -1 , +2.8 Tmol Si yr -1 ). Subsequently, we investigate rates of mineral dissolution and authigenic clay and carbonate formation in marine sediments applying reactive transport modeling, porewater data and mass balance calculations. Our best estimates for net fluxes across the sediment/water interface (dissolution–mineral formation) result as +1.5 Tmol Na yr -1 , -2.5 Tmol K yr -1 , -2.0 Tmol Mg yr -1 , +2.5 Tmol Ca yr -1 , and +1.9 Tmol Si yr -1 where most of the Na and Ca release is induced by plagioclase dissolution, K is taken up in authigenic clays and Mg is removed from solution by authigenic clay and carbonate formation. We conclude that the alkalinity of seawater is not significantly affected by marine silicate alteration since cation release fluxes (Na, Ca) are as high as cation uptake fluxes (K, Mg) on equivalent basis. Moreover, marine silicate weathering and reverse weathering are closely coupled since Al required for clay formation is mostly provided by feldspar dissolution while Al removal in authigenic clay promotes and maintains feldspar dissolution in marine sediments. Authigenic carbonate formation in anoxic subsurface sediments sequesters significant amounts of carbon (2.5 Tmol C yr -1 ) according to our estimates where most of the Ca and alkalinity required for carbonate formation are provided by the dissolution of Ca-bearing silicate minerals. This hidden sedimentary cycle provides a sink for dissolved inorganic carbon that may drive a slow draw-down of atmospheric CO 2 on geological timescales. Marine silicate alteration has an even stronger effect on the geochemical evolution of seawater by generating large fluxes of dissolved K, Mg, Ca and Si.
期刊介绍:
The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.