Silicon isotopic re-equilibration during amorphous silica precipitation and implications for isotopic signatures in geochemical proxies

Fernandez, Nicole; Zhang, Xu; Druhan, Jennifer L.

doi:10.1016/j.gca.2019.07.029

Cited by 24 publications

(47 citation statements)

References 96 publications

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“…This occurs either by a steady-state fractionation where the final solid has the same Si isotope composition as the starting fluid (assuming all DSi precipitates), 30 Si solid−hyporheic zone solution = [δ 30 Si solid −δ 30 Si hyporheic zone solution ] ≈ 0 ; or by unidirectional kinetic isotope fractionation where the final solid has a lighter isotope composition than the starting fluid, 30 Si solid−hyporheic zone solution ≈<0 (Frings et al, 2016 and references therein). This is assuming no re-equilibration of Si isotopes in amorphous silica after precipitation (Fernandez et al, 2019). Unidirectional kinetic isotope fractionation occurs if (i) there is a closed system with no Si inputs or outputs; (ii) there is no change to the δ 30 Si composition of DSi in the starting solution;…”

Section: Cryogenic Amorphous Silica Precipitationmentioning

confidence: 99%

Silicon Isotopes Reveal a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica

et al. 2020

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In high latitude environments, silicon is supplied to river waters by both glacial and nonglacial chemical weathering. The signal of these two end-members is often obscured by biological uptake and/or groundwater input in the river catchment. McMurdo Dry Valleys streams in Antarctica have no deep groundwater input, no connectivity between streams and no surface vegetation cover, and thus provide a simplified system for us to constrain the supply of dissolved silicon (DSi) to rivers from chemical weathering in a glacial environment. Here we report dissolved Si concentrations, germanium/silicon ratios (Ge/Si) and silicon isotope compositions (δ 30 Si DSi) in Crescent Stream, McMurdo Dry Valleys for samples collected between December and February in the 2014−2015, 2015−2016, and 2016−2017 austral seasons. The δ 30 Si DSi compositions and DSi concentrations are higher than values reported in wet-based glacial meltwaters, and form a narrow cluster within the range of values reported for permafrost dominated Arctic Rivers. High δ 30 Si DSi compositions, ranging from +0.90 to +1.39 , are attributed to (i) the precipitation of amorphous silica during freezing of waters in isolated pockets of the hyporheic zone in the winter and the release of Si from unfrozen pockets during meltwater-hyporheic zone exchange in the austral summer, and (ii) additional Si isotope fractionation via long-term Si uptake in clay minerals and seasonal Si uptake into diatoms superimposed on this winter-derived isotope signal. There is no relationship between δ 30 Si DSi compositions and DSi concentrations with seasonal and daily discharge, showing that stream waters contain DSi that is in equilibrium with the formation of secondary Si minerals in the hyporheic zone. We show that δ 30 Si DSi compositions can be used as tracers of silicate weathering in the hyporheic zone and possible tracers of freeze-thaw conditions in the hyporheic zone. This is important in the context of the ongoing warming in McMurdo Dry Valleys and the supply of more meltwaters to the hyporheic zone of McMurdo Dry Valley streams.

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Section: Cryogenic Amorphous Silica Precipitationmentioning

confidence: 99%

Silicon Isotopes Reveal a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica

et al. 2020

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“…We derive growth diagrams as a function of the various kinetic parameters involved and discuss the influence of the seed characteristics. We finally apply our formalism to the precipitation of amorphous silica particles and propose an alternative interpretation of recent experimental results 10,11 .…”

Section: Introductionmentioning

confidence: 81%

“…The application to the synthesis of amorphous silica nanoparticles in the conditions of Ref. 11 in the next section clearly highlights this failure.…”

Section: Discussionmentioning

confidence: 99%

“…In a number of cases, it proceeds via the formation of precursors or seeds under specific conditions prior to the synthesis of the desired object. Seedmediated methods have indeed often been used to obtain monodispersed or shape-selected particles-as in the case of gold NPs 8,9 -or simply because it accelerates the growth kinetics by providing reactive surfaces for the nucleation of secondary particles 10,11 . Examples scan a wide range of applications, including, among others, the precipitation of phosphate minerals onto magnetite seeds 12 , formation of calcium oxalate crystals using cal-cite seeds 13 , the selective formation of zeolites from coal fly ash 14 , industrial applications of nucleation seeding in the field of green cements hydration 15 , or formation of amorphous silica NPs 10,11,16,17 .…”

Section: Introductionmentioning

confidence: 99%

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Modelling the precipitation of nanoparticles in a closed medium in the presence of seeds: Application to amorphous silica synthesis

Noguera¹,

Fritz

Clément

et al. 2021

Journal of Colloid and Interface Science

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“…Mineralogical studies of La Selva soils indicate the ongoing conversion of kaolinite into mostly amorphous Al‐Si oxides (some combination of allophane, halloysite, and/or gibbsite) (Kautz & Ryan, 2003; Kleber et al., 2007; Sollins et al., 1994), as discussed in more detail below. Multiple recent experimental studies have shown that

{normalΔ}^{30} {Si}_{s e c - d i s s}

fractionation factors associated with amorphous silica and Si‐Al oxide precipitation can range from –5 to 0‰, with higher fractionation induced by far‐from‐equilibrium conditions (Fernandez et al., 2019; Oelze et al., 2014, 2015; Roerdink et al., 2015). Similarly,

{normalΔ}^{74} {Ge}_{s e c - d i s s}

during reversible Ge adsorption onto Fe (oxy)hydroxides was smaller (–1.7 ‰) than during irreversible coprecipitation (down to –4.4‰), likely representing dominantly close to equilibrium and far‐from‐equilibrium conditions, respectively (Pokrovsky et al., 2014).…”

Section: Discussionmentioning

confidence: 99%

Ge and Si Isotope Behavior During Intense Tropical Weathering and Ecosystem Cycling

Baronas

West

Burton

et al. 2020

Global Biogeochemical Cycles

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Chemical weathering of volcanic rocks in warm and humid climates contributes disproportionately to global solute fluxes. Geochemical signatures of solutes and solids formed during this process can help quantify and reconstruct weathering intensity in the past. Here, we measured silicon (Si) and germanium (Ge) isotope ratios of the soils, clays, and fluids from a tropical lowland rainforest in Costa Rica. The bulk topsoil is intensely weathered and isotopically light (mean ± 1σ: δ30Si = −2.1 ± 0.3‰, δ74Ge = −0.13 ± 0.12‰) compared to the parent rock (δ30Si = −0.11 ± 0.05‰, δ74Ge = 0.59 ± 0.07‰). Neoforming clays have even lower values (δ30Si = −2.5 ± 0.2‰, δ74Ge = −0.16 ± 0.09‰), demonstrating a whole‐system isotopic shift in extremely weathered systems. The lowland streams represent mixing of dilute local fluids (δ30Si = 0.2 − 0.6‰, δ74Ge = 2.2 − 2.6‰) with solute‐rich interbasin groundwater (δ30Si = 1.0 ± 0.2‰, δ74Ge = 4.0‰). Using a Ge‐Si isotope mass balance model, we calculate that 91 ± 9% of Ge released via weathering of lowland soils is sequestered by neoforming clays, 9 ± 9% by vegetation, and only 0.2 ± 0.2% remains dissolved. Vegetation plays an important role in the Si cycle, directly sequestering 39 ± 14% of released Si and enhancing clay neoformation in surface soils via the addition of amorphous phytolith silica. Globally, volcanic soil δ74Ge closely tracks the depletion of Ge by chemical weathering (τGe), whereas δ30Si and Ge/Si both reflect the loss of Si (τSi). Because of the different chemical mobilities of Ge and Si, a δ74Ge‐δ30Si multiproxy system is sensitive to a wider range of weathering intensities than each isotopic system in isolation.

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Silicon isotopic re-equilibration during amorphous silica precipitation and implications for isotopic signatures in geochemical proxies

Cited by 24 publications

References 96 publications

Silicon Isotopes Reveal a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica

Silicon Isotopes Reveal a Non-glacial Source of Silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica

Modelling the precipitation of nanoparticles in a closed medium in the presence of seeds: Application to amorphous silica synthesis

Ge and Si Isotope Behavior During Intense Tropical Weathering and Ecosystem Cycling

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