Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(III) and hematite

Skulan, Joseph L.; Beard, Brian L.; Johnson, Clark M.

doi:10.1016/s0016-7037(02)00902-x

Cited by 281 publications

(248 citation statements)

References 34 publications

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“…The precipitation of amorphous silica favours light Si (De La Rocha et al, 1997;Ziegler et al, 2005;BasileDoelsch, 2006). Fe precipitation by partial oxidation is dominated by ferric oxyhydroxide which is ~1.5‰ heavier than Fe(II) aq (Bullen et al, 2001;Skulan et al, 2002;Welch et al, 2003;Croal et al, 2004;Anbar et al, 2005). Potential Fe and Si isotope fractionation of the precipitates is illustrated in Figure 8.…”

Section: Significance Of Bulk Fe and Si Isotope Composition In The Olmentioning

confidence: 99%

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Steinhoefel

Horn

Blanckenburg

2009

Geochimica et Cosmochimica Acta

136

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We have detected micrometer-scale differences in Fe and Si stable isotope ratios between coexisting minerals and between layers of banded iron formation (BIF) using an UV femtosecond laser ablation system connected to a MC-ICP-MS. In the magnetite-carbonate-chert BIF from the Archean Old Wanderer Formation in the Shurugwi Greenstone Belt (Zimbabwe), magnetite shows neither intra-nor inter-layer trends giving overall uniform  56 Fe values of ~0.9‰, but exhibits intra-crystal zonation. Bulk iron carbonates are also relatively uniform at near-zero values, however their individual  56 Fe value is highly composition-dependent: both siderite and ankerite and mixtures between both are present, and  56 Fe end member values are 0.4‰ for siderite and -0.7‰ for ankerite. The data suggest either an early diagenetic origin of magnetite and iron carbonates by the reaction of organic matter with ferric oxyhydroxides catalysed by Fe(III)-reducing bacteria; or more likely an abiotic reaction of organic carbon and Fe(III) during low-grade metamorphism. Si isotope composition of the Old Wanderer BIF also shows significant variations with  30 Si values that range between -1.0 and -2.6‰ for bulk layers. These isotope compositions suggest rapid precipitation of the silicate phases from hydrothermal-rich waters. Interestingly, Fe and Si isotope compositions of bulk layers are covariant and are interpreted as largely primary signatures. Moreover, the changes of Fe and Si isotope signatures between bulk layers directly reflect the upwelling dynamics of hydrothermal-rich water which govern the rates of Fe and Si precipitation and therefore also the development of layering. During periods of low hydrothermal activity, precipitation of only small amounts of ferric oxyhydroxide was followed by complete reduction with organic carbon during diagenesis resulting in carbonate-chert layers. During periods of intensive hydrothermal activity, precipitation rates of ferric oxyhydroxide were high, and subsequent diagenesis triggered only partial reduction, forming magnetite-carbonate-chert layers. We are confident that our micro-analytical technique is able to detect both the solute flux history into the sedimentary BIF precursor, and the BIF's diagenetic history from the comparison between coexisting minerals and their predicted fractionation factors.

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Section: Significance Of Bulk Fe and Si Isotope Composition In The Olmentioning

confidence: 99%

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Steinhoefel

Horn

Blanckenburg

2009

Geochimica et Cosmochimica Acta

136

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“…Experimental data on aqueous Fe species, Fe-oxides and Fe-carbonates have been documented and demonstrate that the largest Fe isotope fractionations are produced during redox reactions in both biologically mediated (Brantley et al, 2001Anbar, 2004;Johnson et al, 2004;Beard et al, 1999Beard et al, ,2003Icopini et al, 2004;Croal et al, 2004) and abiotic systems (Anbar et al, 2000;Skulan et al, 2002Brantley et al, 2004Welch et al, 2003;Matthews et al, 2004;Teutsch et al, 2005;Jang et al, 2008, Handler et al, 2009McAnena, 2009, Beard et al, 2010. Smaller, but significant fractionations have been seen in abiotic non-redox reactions (Wiesli et al, 2004;Wiedehold et al, 2006;Dideriksen et al, 2008;Mikutta et al, 2009), including the ligand-exchange process involved in mackinawite (FeS m ) formation (Butler et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Experimental determination of the equilibrium Fe isotope fractionation between and FeSm (mackinawite) at 25 and 2°C

Guilbaud

Butler

Ellam

et al. 2011

Geochimica et Cosmochimica Acta

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“…Scavenging and the precipitation of DFe also result in δ 56 Fe fractionation (9,11,29). The contribution of this particlemediated δ 56 Fe fractionation was explored on a third voyage in 2011 by following changes in δ…”

mentioning

confidence: 99%

“…We note that there are caveats associated with this approach, such as the potential for the formation of multiple particulate Fe phases with differing isotope fractionation factors (11); in particular, phases formed under kinetic control have a different δ 56 Fe composition compared with phases formed under equilibrium control (30). However, our approach is justified as it represents Fe isotopic fractionation under the relevant marine conditions (i.e., well-oxygenated waters at seawater pH) for DFe loss from solution by scavenging and/or mineral precipitation under abiotic conditions within the deeper water column (9). As DFe was lost from solution, its δ 56 Fe composition increased from ∼0.07‰ to 1.73‰.…”

mentioning

confidence: 99%

Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom

Ellwood

Hutchins

Lohan

et al. 2014

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

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The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.iron isotopes | marine biogeochemical cycles | trace metals | phytoplankton blooms | GEOTRACES

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Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(III) and hematite

Cited by 281 publications

References 34 publications

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Experimental determination of the equilibrium Fe isotope fractionation between and FeSm (mackinawite) at 25 and 2°C

Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom

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