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| Titel |
Fractionation of iron species and iron isotopes in the Baltic Sea euphotic zone |
| VerfasserIn |
J. Gelting, E. Breitbarth, B. Stolpe, M. Hassellöv, J. Ingri |
| 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 ; 7, no. 8 ; Nr. 7, no. 8 (2010-08-23), S.2489-2508 |
| Datensatznummer |
250004935
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| Publikation (Nr.) |
 copernicus.org/bg-7-2489-2010.pdf |
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| Zusammenfassung |
| To indentify sources and transport mechanisms of iron in a coastal marine
environment, we conducted measurements of the physiochemical speciation of
Fe in the euphotic zone at three different locations in the Baltic Sea. In
addition to sampling across a salinity gradient, we conducted this study
over the spring and summer season. Moving from the riverine input
characterized low salinity Bothnian Sea, via the Landsort Deep near
Stockholm, towards the Gotland Deep in the Baltic Proper, total Fe
concentrations averaged 114, 44, and 15 nM, respectively. At all three
locations, a decrease in total Fe of 80–90% from early spring to summer
was observed. Particulate Fe (PFe) was the dominating phase at all stations
and accounted for 75–85% of the total Fe pool on average. The Fe isotope
composition (δ 56Fe) of the PFe showed constant positive values
in the Bothnian Sea surface waters (+0.08 to +0.20‰). Enrichment of heavy Fe
in the Bothnian Sea PFe is possibly associated to input of aggregated land
derived Fe-oxyhydroxides and oxidation of dissolved Fe(II). At the Landsort
Deep the isotopic fractionation of PFe changed between −0.08‰ to +0.28‰ over
the sampling period. The negative values in early spring indicate transport
of PFe from the oxic-anoxic boundary at ∼80 m depth. The average
colloidal iron fraction (CFe) showed decreasing concentrations along the
salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM, and Gotland Deep
0.5 nM. Field Flow Fractionation data indicate that the main colloidal
carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid
associated compound, likely of riverine origin. A strong positive
correlation between PFe and chl-a indicates that cycling of suspended Fe is
at least partially controlled by primary production. However, this
relationship may not be dominated by active uptake of Fe into phytoplankton,
but instead may reflect scavenging and removal of PFe during phytoplankton
sedimentation. |
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