气候变化领域集成服务门户(CCPortal): Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite

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DOI	10.1016/j.epsl.2020.116540
	Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite
	Sherman D.M.; Little S.H.
发表日期	2020
ISSN	0012821X
卷号	549
英文摘要	In the oceans, Cu is strongly scavenged by ferromanganese (Fe-Mn) crusts. The isotopic fractionation of Cu between seawater and crusts provides insight into the mechanisms of trace metal cycling in the oceans. Dissolved Cu in seawater is isotopically heavy (+0.66±0.19‰) relative to Cu in crusts (+0.31±0.24‰). The primary mineral phase sorbing divalent trace metals in Fe-Mn crusts is birnessite. Recent laboratory measurements show that isotopically light Cu is preferentially sorbed on birnessite, with a fractionation factor of 0.45±0.18‰. Here, we use first-principles (quantum mechanical) calculations to predict the isotopic fractionation between aqueous Cu2+ complexes and Cu as a surface complex on birnessite. We find that isotopic fractionation between the Cu(H2O)5+ complex and sorbed Cu should be 0.49‰ (at 25 °C), in close agreement with experiments, confirming that these experimental results reflects equilibrium fractionation. We then predict the isotopic fractionation between dissolved inorganic Cu in seawater and birnessite given the thermodynamic speciation of dissolved Cu at pH 8. We find dissolved inorganic Cu should be 0.94‰ (at 5 °C) heavier than Cu sorbed to birnessite. This value is substantially greater than the observed fractionation between seawater and Fe-Mn crusts (Δsw-fmc ≈+0.35‰). Moreover, it is well established that dissolved Cu in seawater is strongly complexed by organic ligands. Based on model Cu complexes and published experimental data, we estimate that fractionation of Cu by organic ligands should increase the equilibrium fractionation between seawater and Fe-Mn crusts by 0.2 to 1.5‰ to yield Δsw-fmc = +1.1 to 2.4‰. We conclude that Cu in marine Fe-Mn crusts in not in isotopic equilibrium with dissolved Cu in seawater, and consider the possible explanations of this surprising finding. © 2020 The Author(s)
关键词	ab initio birnessite copper isotope ferromanganese crust marine
英文关键词	Binary alloys; Calculations; Dissolution; Ferroalloys; Forecasting; Iron alloys; Iron ores; Isotopes; Ligands; Manganese alloys; Quantum theory; Seawater; Trace elements; Ab initio prediction; Equilibrium fractionations; Ferromanganese crusts; Fractionation factors; Isotope fractionation; Isotopic fractionations; Laboratory measurements; Thermodynamic speciation; Copper compounds; birnessite; copper; crust; disequilibrium; ferromanganese deposit; isotopic fractionation; marine environment; prediction; sorption
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202886
作者单位	School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom; Department of Earth Sciences, University College LondonWC1E 6BT, United Kingdom
推荐引用方式 GB/T 7714	Sherman D.M.,Little S.H.. Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite[J],2020,549.
APA	Sherman D.M.,&Little S.H..(2020).Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite.Earth and Planetary Science Letters,549.
MLA	Sherman D.M.,et al."Isotopic disequilibrium of Cu in marine ferromanganese crusts: Evidence from ab initio predictions of Cu isotope fractionation on sorption to birnessite".Earth and Planetary Science Letters 549(2020).