Glacial influence on the iron and sulfur cycles in Arctic fjord sediments (Svalbard)

Michaud, Alexander B. and Laufer, Katja and Findlay, Alyssa and Pellerin, André and Antler, Gilad and Turchyn, Alexandra V. and Røy, Hans and Wehrmann, Laura M. and Jørgensen, Bo Barker (2020) Glacial influence on the iron and sulfur cycles in Arctic fjord sediments (Svalbard). Geochimica et Cosmochimica Acta. ISSN 00167037 DOI https://doi.org/10.1016/j.gca.2019.12.033

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Official URL: https://doi.org/10.1016/j.gca.2019.12.033

Abstract

Arctic fjord sediments of Svalbard receive terrestrial material from glacial runoff and organic matter from marine primary productivity. Organic carbon mineralization proceeds primarily through sulfate and iron reduction in the fjord sediment. The ongoing retreat of glaciers in the high Arctic is altering the input of glacial material to the fjords, with unknown consequences for the iron and sulfur cycles in the fjord sediments. We measured sulfate reduction rates in sediment cores and analyzed porewater geochemistry, then compared these results to long-term sediment incubations to determine the rates of iron reduction and sulfide oxidation in three glacially influenced fjords on the west coast of Spitsbergen, Svalbard. Despite an abundance of glacially-sourced Fe(III)-oxide minerals, active sulfate reduction took place throughout the sediment. Analyses of the sulfur and oxygen isotopic composition of porewater sulfate and sulfate concentrations suggest that sulfide produced from biological sulfate reduction is reoxidized to sulfate. Long-term sediment incubations indicated sulfide oxidation at all three stations. The rate of sulfide oxidation was controlled by both the rate of sulfate reduction and the quantity and reactivity of Fe(III)-oxides. In our experimental incubations, we detected a decrease in Fe(III) content of the 0.5 M HCl and ascorbate-extractable fractions, but not in the 6 M HCl fraction, indicating that the highly reactive Fe(III) fraction is utilized by microorganisms and serves as the oxidant for sulfide oxidation. Our results show that sulfide oxidation in glacially-influenced fjord sediments is a wide-spread geochemical process. Further warming will drive glacial retreat onto land, where sediment-laden glacial meltwater will be altered during flow through proglacial streams and lakes before entering the marine environment. Fjord sediments will likely become more sulfidic, as glaciers deliver less particulate, highly-reactive metal oxides to the marine environment.

Item Type: Article
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Geochimica et Cosmochimica Acta
Identification Number: https://doi.org/10.1016/j.gca.2019.12.033
Depositing User: Sarah Humbert
Date Deposited: 03 Mar 2020 10:28
Last Modified: 03 Mar 2020 10:28
URI: http://eprints.esc.cam.ac.uk/id/eprint/4642

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