The Biogeochemistry of the Active Layer and Shallow Permafrost in a High Arctic Fjord Valley, Svalbard

Rising air temperatures are exposing carbon in Arctic permafrost to decomposition by microorganisms. This is predicted to amplify the response of Earth’s climate system to the anthropogenic forcing of climate. However, the timing and magnitude of this climate feedback are uncertain because of the complex effects of permafrost landscape sedimentation and hydrology upon microbial decomposition of the carbon. This thesis explores the influence of landscape development on biogeochemical processes in continuous permafrost in Svalbard. Fjord valley infills and raised beaches are landforms developed as a direct consequence of deglaciation. Biogeochemical analyses of permafrost cores and water from the active layer were undertaken for three contrasting wetlands situated on these landforms. Chapter 3 demonstrates that the accumulation of organic carbon in fjord valley infills regulates biogeochemical processes, with pyrite oxidation being most pronounced in the drier, organic-poor wetland. In contrast, in the saturated groundwater-fed, organic-rich wetland, there are signs of iron- and sulfate-reduction, pyrite and siderite precipitation and methanogenesis. Chapter 4 shows that the degradation of an ice-wedge polygon situated on intra-beach sediments results in the degraded polygon developing more oxidising conditions, with a decrease in iron reduction, and decreased preservation of pyrite and siderite. Chapter 5 shows that concentrations of carbon dioxide are substantially higher than concentrations of methane in the pore water, owing to microbial respiration using ferric iron and sulfate as electron acceptors. Where methane is detected, hydrogenotrophic methanogenesis is the dominant pathway of methanogenesis. In the degraded ice-wedge polygon, the degradation causes oxidation and a decoupling of the relationship between the concentration of methane and the content of organic carbon. This implies that the production of carbon dioxide during the aerobic respiration of peat becomes increasingly important as ice-wedge polygons degrade. As air temperatures continue to rise in the high Arctic, degradation of ice-wedge polygons and the resultant drainage of water from the landscape are likely to result in pyrite and siderite oxidation and aerobic respiration of organic carbon.