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| Titel |
Redox chemistry of shallow permafrost porewaters in western Spitsbergen |
| VerfasserIn |
Eleanor Jones, Jade Rogers, Ebbe Bak, Kai Finster, Andy Hodson, Gunnar Mallon, Kelly Redeker, Steve Thornton, Jacob Yde |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149534
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| Publikation (Nr.) |
 EGU/EGU2017-13891.pdf |
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| Zusammenfassung |
| The western coast of Spitsbergen, located in the zone of continuous permafrost, is kept
relatively warm for its latitude by the north Atlantic current. This sensitivity to oceanic and
atmospheric warming provides an early warning system for the response of permafrost to
climate change. This response includes the release of stored organic carbon and
nutrients, which can lead to increased greenhouse gas (GHG) emissions from Arctic
wetlands. The aims of this study are to i) develop a methodology to investigate in-situ
processes contributing to GHG emissions in shallow permafrost, and ii) correlate the
geochemical properties of these permafrost sediments with their potential to support GHG
emission.
The focus of this project is on three locations within 10 kilometres of Longyearbyen,
Western Spitsbergen, Svalbard. All locations were covered by warm-based ice during the Last
Glacial Maximum, and so it was only after the deglaciation around 10,000 years ago that
permafrost aggraded. After deglaciation, the following depositional environments
typical of Svalbard formed and were the subject of this study: i) a sequence of
raised beaches, formed due to isostatic rebound, and ii) a prograding delta overlain
by aeolian sediments. Ice-wedge polygons and wetlands developed at all study
sites.
Each location was drilled to a depth of 2 metres. The extracted sediment cores were
transported frozen and stored at -18˚ C. Cores were subdivided at 2 centimetre depth
resolution and the samples were equilibrated anaerobically with deionised, degassed water in
sealed vials. Concentrations of methane and carbon dioxide in the vial headspace, the
chemistry of the supernatant, and the initial moisture content of the sediments were
determined.
Results show a zonation of redox chemistry with depth. Low redox chemistries,
indicating anoxia, appear only below 60 cm depth. A correlation of ferrous iron and
sulphate is also clear, indicative of the process of sulphide oxidation via reduction of
ferrous to ferric iron (below 60 cm). Concentrations of dissolved methane in the
porewaters are low (<20 μmol l−1) and concentrations of dissolved carbon dioxide
are higher (<4000 μmol l−1). Nitrate concentrations are high throughout (∼ 0.25
mmol l−1). These results point to relatively high redox environments, in which
the production of carbon dioxide dominates over the production of methane. This
indicates that methanogenesis is limited in these environments by competing anaerobic
respiration processes and/or counteracted by anaerobic oxidation of methane, which
need to be accounted for in predictions of the future permafrost carbon feedback. |
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