Isotopic Fractionation during Diffusion of Transition Metal Ions in Solution

Rodushkin, Ilia; Stenberg, Anna; Andrén, Henrik; Malinovsky, Dmitry; Baxter, Douglas C.

doi:10.1021/ac035296g

Cited by 104 publications

(81 citation statements)

References 23 publications

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“…An additional isotope effect will be conferred by the difference in diffusivity between the different Zn isotopes. 64Zn2+ will diffuse towards the cell more quickly than 66 Zn 2 +, and the difference in aqueous diffusivity of free Zn is equivalent to a preference for light Zn uptake by A66Zn = -0.06%0o (Rodushkin et al, 2004). Together, the free Zn/Zn-EDTA equilibrium isotope effect and the difference in isotope diffusivity can account for the entire -0.2%o fractionation observed under high-affinity transport.…”

Section: Biological Zn Isotope Fractionationmentioning

confidence: 99%

The marine biogeochemistry of zinc isotopes

John¹

2007

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Zinc (Zn) stable isotopes can record information about important oceanographic processes. This thesis presents data on Zn isotopes in anthropogenic materials, hydrothermal fluids and minerals, cultured marine phytoplankton, natural plankton, and seawater. By measuring Zn isotopes in a diverse array of marine samples, we hope to understand how Zn isotopes are fractionated in the oceans and how Zn isotopes may be used as tracers of marine biogeochemical processes. Common forms of anthropogenic Zn had 66 6Zn from +0.08 %o to +0.32 %o, a range similar to Zn ores and terrigenous materials. Larger variations were discovered in hydrothermal fluids and minerals, with hydrothermal fluids ranging in 6 66 Zn from 0.02 %o to +0.93 %o, and chimney minerals ranging from -0.09 %o to +1.17 %o. Lower-temperature vent systems had higher 86 6 6 Zn values, suggesting that precipitation of isotopically light Zn sulfides drives much of the Zn isotope fractionation in hydrothermal systems. In cultured diatoms, a relationship was discovered between Zn transport by either high-affinity or low-affinity uptake pathways, and the magnitude of Zn isotope fractionation. We established isotope effects of 86 6 Zn = -0.2 %o for high-affinity uptake and 8 66 Zn = -0.8 %o for low-affinity uptake. This work is the first to describe the molecular basis for biological fractionation of transition metals. Biological fractionation of Zn isotopes under natural conditions was investigated by measuring Zn isotopes in plankton collected in the Peru Upwelling Region and around the world. Seawater dissolved Zn isotopes also reflect the chemical and biological cycling of Zn. The 6 66 Zn of deep seawater in the North Pacific and North Atlantic is about 0.5%0, and the dissolved 8 66 Zn gets lighter in the upper water column. This is unexpected based our observations of a biological preference for uptake of light Zn isotopes, and suggests that Zn transport to deep waters may occur by Zn adsorption to sinking particles rather than as primary biological Zn. The thesis, by presenting data on several important aspects of Zn isotope cycling in the oceans, lays the groundwork for further use of Zn isotopes as a marine biogeochemical tracer.

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Section: Biological Zn Isotope Fractionationmentioning

confidence: 99%

The marine biogeochemistry of zinc isotopes

John¹

2007

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“…More likely is a kinetic effect during the transport of soluble Fe in a fluid phase if advection is negligible and molecular diffusion dominates. Despite the presence of Fe(II) aq as hexaquo complex in aqueous solution which decreases the relative mass differences between isotopes and therefore limits kinetic fractionation effects (Richter et al, 2006), an experimental study of (Rodushkin et al, 2004) postulates a discrimination of dissolved 56 Fe relative to 54 Fe of -0.3‰ by diffusion. 2) If siderite and magnetite form simultaneously by abiotic reactions and compete for a limited reservoir of Fe(II) aq during diagenesis, their isotope composition might affect each other.…”

Section: The Significance Of Zoned Magnetite Crystalsmentioning

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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“…The shift in D 66 Zn occurs within a similar range of Zn concentrations as the shift between the predominance of high-and low-affinity uptake, indicating that each transport pathway has a unique isotope effect. Error bars represent external reproducibility (2s SD).2712 Notes 5 20.06% (Rodushkin et al 2004). Together, the equilibrium isotope effect between free Zn and Zn-EDTA plus the difference in isotope diffusivity can account for the entire 20.2% fractionation observed under high-affinity transport.…”

mentioning

confidence: 97%

“…5 20.06% (Rodushkin et al 2004). Together, the equilibrium isotope effect between free Zn and Zn-EDTA plus the difference in isotope diffusivity can account for the entire 20.2% fractionation observed under high-affinity transport.…”

mentioning

confidence: 98%

Zinc isotope fractionation during high‐affinity and low‐affinity zinc transport by the marine diatom Thalassiosira oceanica

John

Geis

Saito

et al. 2007

Limnology & Oceanography

193

181

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Abstract-We have measured the isotopic fractionation of zinc (Zn) during uptake by the marine diatom Thalassiosira oceanica cultured at a range of free Zn 2+ concentrations representative of the natural range from coastal and oligotrophic regions of the ocean. Harvested cells were rinsed with either plain seawater or a wash designed to remove adsorbed extracellular metals. Unwashed cells had much higher levels of Zn and were isotopically heavier than the media, indicating a positive isotope effect for extracellular Zn adsorption. Internalized Zn, measured in washed cells, was isotopically lighter than the media. The magnitude of Zn isotope fractionation changed with free Zn 2+ concentration, corresponding to a switch on the part of T. oceanica between the predominance of high-and low-affinity Zn transport pathways. The total isotope effect for uptake (D 66 Zn) was 20.2% for high-affinity uptake at low Zn concentrations and 20.8% at the highest Zn concentrations, where lowaffinity uptake is dominant. To our knowledge, this is the first study to describe a physiological basis for biological metal isotope fractionation during transport across the cell membrane. Similar high-and low-affinity Zn transport pathways are common among marine phytoplankton, suggesting that the processes described here are an important factor in natural marine Zn isotope variations. Zinc (Zn) is an essential biological nutrient in the oceans where the concentration distribution of Zn is controlled largely by phytoplankton Zn uptake and remineralization. When micronutrients such as Zn are transported across a cell membrane, some isotopes may be taken up more quickly than others. This biological fractionation may be recorded as variations in the ratio of 66 Zn : 64 Zn found in environmental samples. Biological processes have been invoked to explain Zn isotope variations in seawater (Bermin et al. 2006), marine sediments (Maréchal et al. 2000;Pichat et al. 2003), manganese nodules, and marine particles (Maréchal et al. 2000). Measuring the magnitude of biological Zn isotope fractionation is crucial to interpreting these natural signals. Zn isotope effects of up to 0.5% in d 66 Zn have been observed in land plants ) and phytoplankton (Gélabert et al. 2006) By accurately measuring the magnitude of biological Zn isotope fractionation, changes in the isotopic composition of Zn in seawater or ancient sediments can be directly related to the extent of biological Zn uptake in surface waters. High-and low-affinity transport systems for Zn have been identified in many organisms, including several species of fish, yeast (Zhao and Eide 1996), plants such as wheat (Hacisalihoglu et al. 2001), and several species of marine phytoplankton (Sunda andHuntsman 1992, 1998). ZIPfamily proteins, many of which are specific Zn transporters, have been found in bacteria, archaea, and many eukaryotes, and putative ZIP homologs have recently been identified in the genome of the diatom Thalassiosira pseudonana. For all eukaryotic phytoplankton studied, including thr...

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Isotopic Fractionation during Diffusion of Transition Metal Ions in Solution

Cited by 104 publications

References 23 publications

The marine biogeochemistry of zinc isotopes

The marine biogeochemistry of zinc isotopes

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

Zinc isotope fractionation during high‐affinity and low‐affinity zinc transport by the marine diatom Thalassiosira oceanica

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