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| Titel |
Isotope fractionation between dissolved and suspended particulate Fe in the oxic and anoxic water column of the Baltic Sea |
| VerfasserIn |
M. Staubwasser, R. Schoenberg, F. Blanckenburg, S. Krüger, C. Pohl |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 1 ; Nr. 10, no. 1 (2013-01-15), S.233-245 |
| Datensatznummer |
250017469
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| Publikation (Nr.) |
 copernicus.org/bg-10-233-2013.pdf |
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| Zusammenfassung |
| Fe isotope ratios and concentrations of dissolved Fe (Fedis,
< 0.45 μm) and of suspended particulate Fe (FeSPM)
were analyzed from a depth profile through the anoxic Eastern Gotland Basin
water column, Baltic Sea. Results show a sharp gradient in
δ56Fedis across the ferruginous layer with
δ56Fedis = −0.4‰ in the euxinic deep
basin and δ56Fedis = +0.3‰ in the oxic
upper water column. The isotopic gradient overlaps with a strong
concentration gradient of Fedis, a concentration maximum in
FeSPM and lower δ56FeSPM values than
δ56Fedis. These features indicate preferential loss of
light Fe isotopes from solution to suspended iron-oxyhydroxides
(FeIOH) during typical oxidative precipitation across the redox
interface. The sign of the overall fractionation,
Δ56FeIOH-Fe(II)(aq) < 0‰, is in
contrast to similar, mostly non-marine redox environments, where
Δ56FeIOH-Fe(II)(aq) > 0‰. The
difference appears to be the result of isotope exchange dominated by reaction
kinetics in the marine water column, rather than equilibrium fractionation
generally inferred for oxidative Fe precipitation elsewhere. High residual
δ56Fedis immediately above the oxic–ferruginous
interface and throughout the oxic water column suggests that any potential
dissolved Fe export from marine reducing waters into the oxic open water
column is enriched in the heavy isotopes. In the deep, mildly euxinic water
column above the level of Fe sulfide saturation, a decreasing δ56FeSPM trend with depth and a generally low δ56Fedis are comparable to trends generally observed in marine
anoxic sediment profiles where microbial reductive Fe dissolution occurs. The
isotope composition of the redox-cycled Fe inventory in anoxic marine basins
mainly reflects the balance between external fluxes, driving the composition
towards crustal δ56Fe values, and intensity of internal recycling,
driving δ56Fe towards negative values. |
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