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TitleBiogeochemical processes in the active layer and permafrost of a high Arctic fjord valley
AuthorJones, E L; Hodson, A J; Thornton, S F; Redeker, K R; Rogers, J; Wynn, P M; Dixon, T; Bottrell, S H; O'Neill, H BORCID logo
SourceFrontiers in Earth Science vol. 8, 342, 2020 p. 1-20, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200053
PublisherFrontiers in Earth Science
Mediapaper; on-line; digital
File formatpdf
AreaSvalbard; Norway
Lat/Long WENS 15.0000 25.0000 79.0000 78.0000
Subjectsgeochemistry; Nature and Environment; Science and Technology; permafrost; permafrost geochemistry; biogeochemistry; iron; carbon; fiords
Illustrationslocation maps; photographs; tables; profiles; plots
ProgramClimate Change Geoscience Permafrost
Released2020 09 02
AbstractWarming of ground is causing microbial decomposition of previously frozen sedimentary organic carbon in Arctic permafrost. However, the heterogeneity of the permafrost landscape and its hydrological processes result in different biogeochemical processes across relatively small scales, with implications for predicting the timing and magnitude of permafrost carbon emissions. The biogeochemical processes of iron- and sulfatereduction produce carbon dioxide and suppress methanogenesis. Hence, in this study, the biogeochemical processes occurring in the active layer and permafrost of a high Arctic fjord valley in Svalbard are identified from the geochemical and stable isotope analysis of aqueous and particulate fractions in sediment cores collected from ice wedge polygons with contrasting water content. In the drier polygons, only a small concentration of organic carbon (<5.40 dry weight%) has accumulated. Sediment cores from these drier polygons have aqueous and solid phase chemistries that imply sulfide oxidation coupled to carbonate and silicate dissolution, leading to high concentrations of aqueous iron and sulfate in the pore water profiles. These results are corroborated by d34S and d18O values of sulfate in active layer pore waters, which indicate the oxidative weathering of sedimentary pyrite utilising either oxygen or ferric iron as oxidising agents. Conversely, in the sediments of the consistently water-saturated polygons, which contain a high content of organic carbon (up to 45 dry weight%), the formation of pyrite and siderite occurred via the reduction of iron and sulfate. d34S and d18O values of sulfate in active layer pore waters from these water-saturated polygons display a strong positive correlation (R2 = 0.98), supporting the importance of sulfate reduction in removing sulfate from the pore water. The significant contrast in the dominant biogeochemical processes between the water-saturated and drier polygons indicates that small-scale hydrological variability between polygons induces large differences in the concentration of organic carbon and in the cycling of iron and sulfur, with ramifications for the decomposition pathway of organic carbon in permafrost environments.
Summary(Plain Language Summary, not published)
This study highlights the importance of landscape evolution and demonstrates that permafrost aggradation and organic carbon accumulation have caused significant changes in the biogeochemical processes and mineral precipitation reactions within this high Arctic floodplain. The contrasting hydrological regimes of the study sites result in marked differences in the accumulation and decomposition of permafrost organic carbon. As air temperatures continue to rise in the high Arctic and as thaw progresses deeper into the permafrost, there are likely to be major changes in the iron, sulfur and carbon cycling in this valley, depending on how permafrost thaw impacts the geomorphology and hydrology of the ice-wedge polygonal terrain.

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