Silicon isotope fractionation during silica precipitation from hot-spring waters: Evidence from the Geysir geothermal field, Iceland

Geilert, Sonja; Vroon, P.Z.; Keller, Nicole; Gudbrandsson, S.; Stefánsson, Andri; Bergen, Manfred J. van

doi:10.1016/j.gca.2015.05.043

Cited by 62 publications

(44 citation statements)

References 108 publications

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“…If the formation of secondary alumino-silicates is limited, the Si concentration in solution may reach supersaturation with respect to amorphous silica, for example upon freezing (Shoji and Masui, 1971;Ping et al, 1988). The precipitation of amorphous silica fractionates Si isotopes (e.g., Li et al, 1995;Geilert et al, 2014Geilert et al, , 2015Roerdink et al, 2015;Oelze et al, 2015), and would add to the Si isotope fractionation induced by clay formation. Consequently, a second working hypothesis is that Si isotope fractionation in soils, if partly caused by amorphous silica precipitation, indi-rectly provides a way to support the formation of metalorganic complexes in soils.…”

Section: Introductionmentioning

confidence: 99%

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Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

Opfergelt

Williams

Cornélis

et al. 2017

Geochimica et Cosmochimica Acta

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Incipient warming of peatlands at high latitudes is expected to modify soil drainage and hence the redox conditions, which has implications for Fe export from soils. This study uses Fe isotopes to assess the processes controlling Fe export in a range of Icelandic soils including peat soils derived from the same parent basalt, where Fe isotope variations principally reflect differences in weathering and drainage. In poorly weathered, well-drained soils (non-peat soils), the limited Fe isotope fractionation in soil solutions relative to the bulk soil (D 57 Fe solution-soil = À0.11 ± 0.12‰) is attributed to proton-promoted mineral dissolution. In the more weathered poorly drained soils (peat soils), the soil solutions are usually lighter than the bulk soil (D 57 Fe solution-soil = À0.41 ± 0.32‰), which indicates that Fe has been mobilised by reductive mineral dissolution and/or ligand-controlled dissolution. The results highlight the presence of Fe-organic complexes in solution in anoxic conditions. An additional constraint on soil weathering is provided by Si isotopes. The Si isotope composition of the soil solutions relative to the soil (D 30 Si solution-soil = 0.92 ± 0.26‰) generally reflects the incorporation of light Si isotopes in secondary aluminosilicates. Under anoxic conditions in peat soils, the largest Si isotope fractionation in soil solutions relative to the bulk soil is observed (D 30 Si solution-soil = 1.63 ± 0.40‰) and attributed to the cumulative contribution of secondary clay minerals and amorphous silica precipitation. Si supersaturation in solution with respect to amorphous silica is reached upon freezing when Al availability to form aluminosilicates is limited by the affinity of Al for metal-organic complexes. Therefore, the precipitation of amorphous silica in peat soils indirectly supports the formation of metal-organic complexes in poorly drained soils. These observations highlight that in a scenario of decreasing soil drainage with warming high latitude peatlands, Fe export from soils as Fe-organic complexes will increase, which in turn has implications for Fe transport in rivers, and ultimately the delivery of Fe to the oceans.

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Section: Introductionmentioning

confidence: 99%

“…EA-2). The light isotopes of Si are known to be preferentially incorporated into amorphous Si (e.g., Li et al, 1995;Geilert et al, 2014Geilert et al, , 2015Roerdink et al, 2015;Oelze et al, 2015), which may contribute to the lighter Si isotope compositions of the HA and H bulk soils relative to the V-BA-GA soils (Fig. 4a).…”

mentioning

confidence: 99%

Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

Opfergelt

Williams

Cornélis

et al. 2017

Geochimica et Cosmochimica Acta

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“…Several purification processes have been proposed to remove sulfur prior to column chemistry (van den Boorn et al 2009, Geilert et al 2015. Others have suggested that instead of removing sulfur, doping both samples and bracketing calibrators with sulfur to the same S/Si mass ratio is valid for sulfate-rich rocks and river water samples (e.g., Hughes et al 2011).…”

mentioning

confidence: 99%

Accurate and Precise Silicon Isotope Analysis of Sulfur‐ and Iron‐Rich Samples by MC‐ICP‐MS

Chen

Lapen

Chafetz

2017

Geostandard Geoanalytic Res

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Silicon isotope determination of sulfur‐rich samples by MC‐ICP‐MS can be challenging because cation‐exchange chromatography used for Si purification does not efficiently remove anionic sulfur species. Results for pure Si standard solutions with addition of sulfate showed shifts of up to +1.04 ± 0.10‰ (2s) in δ30Si. Doping of both standard solutions and samples with S to a fixed S/Si ratio can eliminate the relative change in instrumental mass fractionation due to variable S/Si in samples and also boosts the relative sensitivity of Si by up to 66%. Moreover, Fe hydroxide precipitation during sample processing adsorbs Si resulting in isotopic fractionations. Tests using Fe‐rich samples showed that this could be a major factor for observed shifts in δ30Si. Acidification of the sample and standard solutions to a pH < 1 aggressively dissolved any Fe hydroxide precipitates, even in relatively Fe‐rich samples such as chondrite meteorites. The pH values of the sample solutions were subsequently adjusted to a range of 2–3 by adding ultra‐pure NaOH solutions. The combination of sulfur doping and the pH adjustment protocol ensured a full recovery of Si and proved to be an efficient and reliable method for Si isotope determination of S‐ and Fe‐rich materials.

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“…Fine-scale variation of  30 Si has already been observed in microanalytical studies of ancient ocean floor sediments (Marin-Carbonne et al, 2011;Stefurak et al, 2015;Steinhoefel et al, 2009;, although those heterogeneities were derived in vastly different conditions from the setting of this study. Both settings suggest that, in addition to the bulk Si isotope composition, the range of Geilert et al, 2015). Thus, interpretation of Si isotopes in modern weathering systems requires a parameterization of , rather than a single bulk Si isotope fractionation factor.…”

Section: Implications For Weathering Environmentsmentioning

confidence: 99%

“…In systems in which multiple fractionating processes operated simultanously, attributing Si isotopic signatures to a single fractionating mechanism is difficult and frequently requires the application of additional geochemical tracers. Another unresolved issue is that isotopic fractionation factors associated with precipitation of clays and opals (α precip-aqueous ranging from -0.7‰ to -3.5‰ for the 30 Si/ 28 Si ratio, although this range is strongly affected by kinetic processes (Douthitt, 1982;Geilert et al, 2014Geilert et al, , 2015Li et al, 1994;Milligan et al, 2004). Si isotope fractionation factors are rate dependent (Oelze et al, 2014;Geilert et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai’i

Chemtob

Rossman

Young

et al. 2015

Geochimica et Cosmochimica Acta

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Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai'i, Geochimica et Cosmochimica Acta (2015), doi: http://dx.doi.org/10.1016/j.gca. 2015.07.026 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Silicon isotope fractionation during silica precipitation from hot-spring waters: Evidence from the Geysir geothermal field, Iceland

Cited by 62 publications

References 108 publications

Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

Accurate and Precise Silicon Isotope Analysis of Sulfur‐ and Iron‐Rich Samples by MC‐ICP‐MS

Silicon isotope systematics of acidic weathering of fresh basalts, Kilauea Volcano, Hawai’i

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