Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solutions

DePaolo, Donald J.

doi:10.1016/j.gca.2010.11.020

Cited by 396 publications

(244 citation statements)

References 64 publications

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“…Our finding of the isotopic mass dependence of k wex implies that any ligand-exchange reaction whose rate constant correlates with k wex [mineral dissolution (28,29), metal binding to organic ligands (26,27), and possibly metal attachment to mineral surfaces (13,18,19,21)] should exhibit significant kinetic isotope fractionation. For such reactions, the overall kinetic isotope fractionation (α kinetic ) has a maximum value in conditions where the forward reaction rate is much larger than the backward rate.…”

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confidence: 70%

“…In support of this inference, molecular dynamics (MD) simulations of barium sulfate growth suggest that the kinetics of Ba 2+ attachmentwhich govern barite nucleation and growth (20)-may be ratelimited by the partial desolvation of the metal to form an innersphere surface complex (21). Likewise, experimental (22,23), theoretical (13,24), and molecular simulation studies (25) suggest that the kinetics of metal attachment at calcite surfaces may be related to the dehydration frequency of the metal near the surface. More broadly, the rate constants of several metal ligandexchange reactions [Mg and Ni binding to a range of organic ligands (26,27), the dissolution of orthosilicate minerals containing a range of divalent metals (28,29)] have been shown to correlate with the water-exchange rates of metals in liquid water, k wex (the inverse of the residence time of water in the first solvation shell of the metal).…”

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confidence: 94%

“…Equilibrium Ca isotope fractionation between Ca 2+ (aq) and calcite has not been measured in the laboratory, but studies of deep-sea sedimentary pore fluids suggest that the equilibrium fractionation is negligible: ε eq ∼ 0.0 ± 0.1‰ (12). Growth of calcite from seawater-like aqueous solutions is not likely to be diffusion-limited for Ca, so the isotopic effects are inferred to be due to kinetic effects occurring at the solid/fluid interface (11,13). Diffusion in liquid water can result in kinetic isotopic fractionation (14)(15)(16)(17), but in the case of Ca isotopes, the available data suggest that the largest possible light-isotope enrichment from diffusion-limited growth is ∼0.4‰ in δ 44/40 Ca, which is too small to explain the observations (17).…”

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confidence: 99%

“…In cases where the backward rate is nonnegligible, calculation of α kinetic is straightforward but requires knowledge of the ratio of forward to backward reaction rates (13). In cases for which these rates are not well constrained, the maximum value of Fractionations are reported as both α-values and solid-phase isotopic signatures and were calculated using the MD global γ = 0.049 ± 0.009 and the dynamic fractionation factor defined in Eq.…”

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confidence: 99%

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Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Hofmann

Bourg

DePaolo

2012

Proc. Natl. Acad. Sci. U.S.A.

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Molecular dynamics simulations show that the desolvation rates of isotopes of Li + , K + , Rb + , Ca 2+ , Sr 2+ , and Ba 2+ may have a relatively strong dependence on the metal cation mass. This inference is based on the observation that the exchange rate constant, k wex , for water molecules in the first hydration shell follows an inverse power-law mass dependence (k wex ∝ m −γ ), where the coefficient γ is 0.05 ± 0.01 on average for all cations studied. Simulated waterexchange rates increase with temperature and decrease with increasing isotopic mass for each element. The magnitude of the water-exchange rate is different for simulations run using different water models [i.e., extended simple point charge (SPC/E) vs. four-site transferrable intermolecular potential (TIP4P)]; however, the value of the mass exponent γ is the same. Reaction rate theory calculations predict mass exponents consistent with those determined via molecular dynamics simulations. The simulation-derived mass dependences imply that solids precipitating from aqueous solution under kinetically controlled conditions should be enriched in the light isotopes of the metal cations relative to the solutions, consistent with measured isotopic signatures in natural materials and laboratory experiments. Desolvation effects are large enough that they may be a primary determinant of the observed isotopic fractionation during precipitation.aqueous geochemistry | kinetic isotope effect | ligand exchange N onequilibrium processes are generally recognized as important influences on isotopic fractionation during mineral precipitation, especially at temperatures below a few hundred degrees Celsius (1, 2). Recent work in "nontraditional" stable isotopes (Li, Mg, Ca, Fe, Cd, Cu, etc.) has confirmed this inference and shown that nonequilibrium fractionation must be accounted for to understand global biogeochemical cycles involving these elements (2-5). A key observation is that light isotopes are preferentially incorporated into precipitating solids (6-8)-the opposite direction of enrichment expected for equilibrium fractionation, which depends on bond energetics (9, 10). The origin of this nonequilibrium light-isotope enrichment is a key unknown in the isotopic geochemistry of mineral growth.Calcite grown from aqueous solutions provides an excellent illustration of light-isotope enrichment during precipitation. Synthetically precipitated and natural samples of calcite and aragonite are fractionated relative to aqueous Ca 2+ such that δ 44/40 Ca in calcite is lower by 0.5-2‰ (7, 11). Equilibrium Ca isotope fractionation between Ca 2+ (aq) and calcite has not been measured in the laboratory, but studies of deep-sea sedimentary pore fluids suggest that the equilibrium fractionation is negligible: ε eq ∼ 0.0 ± 0.1‰ (12). Growth of calcite from seawater-like aqueous solutions is not likely to be diffusion-limited for Ca, so the isotopic effects are inferred to be due to kinetic effects occurring at the solid/fluid interface (11, 13). Diffusion in liquid water can r...

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confidence: 94%

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confidence: 99%

mentioning

confidence: 99%

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Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Hofmann

Bourg

DePaolo

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Since incorporation of some elements may depend on precipitation rate (e.g. DePaolo, 2011), it is necessary to quantify these rates across a diurnal time frame when chamber formation is occurring in order to assess the kinetics of element incorporation and thereby proxy-relationships.…”

Section: Chamber Growthmentioning

confidence: 99%

Biomineralization in perforate foraminifera

Nooijer

Spero

Erez

et al. 2014

Earth-Science Reviews

210

190

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a b s t r a c t a r t i c l e i n f oIn this paper, we review the current understanding of biomineralization in perforate foraminifera. Ideas on the mechanisms responsible for the flux of Ca 2+ and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera. From the 1980s onward, tracer experiments, fluorescent microscopy and high-resolution test geochemical analysis have added to existing calcification models. Despite recent insights, no general consensus on the physiological basis of foraminiferal biomineralization exists. Current models include seawater vacuolization, transmembrane ion transport, involvement of organic matrices and/or pH regulation, although the magnitude of these controls remain to be quantified. Disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and/or lack of a more systematic approach to study (dis)similarities between taxa. In order to understand foraminiferal controls on element incorporation and isotope fractionation, and thereby improve the value of foraminifera as paleoceanographic proxies, it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research.

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Minimal influence of recrystallization on middle Miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial Pacific

2016

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Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solutions

Cited by 396 publications

References 64 publications

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Biomineralization in perforate foraminifera

Minimal influence of recrystallization on middle Miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial Pacific

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