The Stability of Fe-Isotope Signatures During Low Salinity Mixing in Subarctic Estuaries.

Conrad, Sarah , Wuttig, Kathrin , Jansen, Nils, Rodushkin, Ilia and Ingri, Johan (2019) The Stability of Fe-Isotope Signatures During Low Salinity Mixing in Subarctic Estuaries. Open Access Aquatic Geochemistry, 25 (5-6). pp. 195-218. DOI 10.1007/s10498-019-09360-z.

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Supplementary data:

Abstract

We have studied iron (Fe)-isotope signals in particles (> 0.22 µm) and the dissolved phase (< 0.22 µm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the Råne and the Kalix, are enriched in Fe and organic carbon (up to 29 µmol/L and up to 730 µmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ56Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH.

Document Type: Article
Keywords: Fe-isotopes; Fe geochemistry; Dissolved and particulate Fe; Organically complexed Fe; Fe(oxy)hydroxides; Salinity gradient; Spring flood
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Refereed: Yes
Open Access Journal?: No
Publisher: Springer
Date Deposited: 13 Dec 2019 13:08
Last Modified: 31 Jan 2022 09:18
URI: https://oceanrep.geomar.de/id/eprint/48480

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