Fractionation of silicon isotopes by marine diatoms during biogenic silica formation

Rocha, Christina L. De La; Brzezinski, Mark A.; DeNiro, Michael J.

doi:10.1016/s0016-7037(97)00300-1

Cited by 327 publications

(389 citation statements)

References 31 publications

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“…However, given that both Fe and Si precipitated simultaneously but with variable intensity as BIFs are characterized by alternating Fe-rich and Si-rich layers, their isotope fractionations must be considered together. 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).…”

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

130

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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

130

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“…A steady state model assumes constant supply and export at equilibrium, while the Rayleigh-type model assumes a fixed input followed by fractional loss or export (in time or space). Results obtained from culture studies have not shown any species or temperature dependence of the Si isotope fractionation factor, which is e Si % À1.1% [De La Rocha et al, 1997]. This degree of mass fractionation has been confirmed by seawater modeling [Cardinal et al, 2005;Reynolds et al, 2006a], but fractionation into in situ formed biogenic opal appears to be somewhat larger, up to e Si % À1.6% [Varela et al, 2004;Cardinal et al, 2007].…”

Section: Resultsmentioning

confidence: 64%

“…[11] The abrupt change of >0.3% in d 30 Si at 2.73 Ma is relatively large compared to the isotopic fractionation factor (e Si ) occurring during biogenic opal production by diatoms [De La Rocha et al, 1997], which was estimated at À1.1% The lowest d 30 Si value corresponds to either 40% or 60% Si utilization, based upon a steady state or Rayleigh-type fractionation model, respectively. The abrupt change at 2.73 Ma is equivalent to a 33% and 18% drop in utilization, on the basis of the same respective models.…”

Section: Resultsmentioning

confidence: 99%

“…The biological utilization of nutrients causes mass-dependent isotope fractionation, with the lighter isotopes being preferentially incorporated into the diatoms' organic matter and frustules during biomineralization. This can be observed in the stable isotope ratios of C ( 13 C/ 12 C), N ( 15 N/ 14 N) and Si ( 30 Si/ 28 Si) [Tieszen, 1978;Altabet and Francois, 1994;De La Rocha et al, 1997], which are expressed in d notation as relative deviations from a standard in parts per thousand [Coplen et al, 2002], e.g., d 13 C, d 15 N and d 30 Si. Despite the importance of Si, only three published studies have so far used Si stable isotopes as proxies for understanding variations in past diatom productivity, or more exactly Si utilization [De La Rocha et al, 1998;Brzezinski et al, 2002;Beucher et al, 2007].…”

Section: Introductionmentioning

confidence: 99%

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Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma

Reynolds

Halliday

2008

Paleoceanography

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[1] The initiation of Northern Hemisphere glaciation in the subarctic North Pacific at $2.73 Ma was marked by an abrupt cessation of high opaline accumulation, considered to result from an increased stratification of the water column that should have led to higher utilization of nutrients in the surface ocean. We present a new stable Si isotope-based record of Si utilization that is hard to reconcile with this model. A drop in 30 Si/ 28 Si by 0.4% at 2.73 Ma is coincident with an increase in bulk N isotope composition. The contrasting utilization records cannot have been both caused by a hydrographic change alone. Excluding a change in the Si:N export ratio, these results either imply a relative increase in silicic acid supplied to the surface waters or a change in its Si isotope composition. While it is impossible to distinguish between these two possibilities, both imply a regional or global change in the Si biogeochemical cycle, potentially caused by an enhanced storage of Si in the underlying deep waters of the Pacific.

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“…Accordingly, measurements of δ 30 Si diatom ( 30 Si/ 28 Si) and δ 29 Si diatom ( 29 Si/ 28 Si) (there is a mass dependent fractionation between the 2 ratios of δ 30 Si = 1.96 x δ 29 Si, measurement of both ratios is a good analytical indicator of sample purity but generally only δ 30 Si diatom is reported), provide information on the availability and rate of silicic acid utilization within the photic zone, which can in turn be related to the global silicon cycle. Importantly, work has indicated that the diatom silicon isotope enrichment factor of −1.1‰ to −1.9‰ is independent of temperature, pCO 2 or other interspecies effects (Spadaro 1983;De La Rocha et al, 1997Milligan et al, 2004;Varela et al, 2004).…”

Section: Silicon Isotopesmentioning

confidence: 99%

Stable isotopes from diatom silica

Leng

Swann

2010

The Diatoms

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Fractionation of silicon isotopes by marine diatoms during biogenic silica formation

Cited by 327 publications

References 31 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

Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma

Stable isotopes from diatom silica

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