Cryolithological and biogeochemical characteristics of the upper permafrost in the Teshekpuk Lake Special Area based on permafrost cores

guido.grosse [ at ]


Permafrost and northern peatlands are a great storage of carbon and also one of the most vulnerable ones. In the course of discussing climate change it is important to estimate how much carbon is stored in the permafrost soils of the Earth and help to evaluate how thawing permafrost may contribute to anthropogenic climate warming. Whether permafrost regions still accumulate carbon or already act as a carbon source is still debated. The Alaska North Slope with its permafrost-affected soils is of general interest in the context of carbon stock investigations. In this study, a multidisciplinary approach was chosen to characterize the upper permafrost in the Teshekpuk Lake Special Area on the Alaska North Slope according to cryolithological, biogeochemical, geochronological, and hydrochemical parameters. Investigations were based on three permafrost cores from erosional upland remnants and one core from a drained thermokarst lake basin that were acquired in Aprils 2010 and 2014 when the active layer was frozen. An attempt was made to analyze depositional dynamics, potential paleoenvironmental changes are discussed, and detailed estimates of soil organic carbon, soil nitrogen and ground ice stocks in Teshekpuk Lake Special Area are presented. Sediment samples were analyzed for ice contents, grain size distribution, biogeochemical parameters (total nitrogen, total carbon, total organic carbon and stable carbon isotopes), and for radiocarbon age. Ground ice was measured for electrical conductivity, pH value and stable water isotopes. The core of the drained thermokarst lake basin shows a succession of lake phases and wetland phases. The first upland core consists of organic-poor deposits, a cryoturbated zone of higher organic content, eolian silt deposits, and a peaty layer on top. The second upland core is characterized by various wetland stages with varying organic carbon content, whereas the third upland core consists of pond ice at the bottom and peaty deposits at the top. Measurements of bulk density, ice content, total organic carbon (TOC) and total nitrogen (TN) enable to estimate ground ice content, soil organic carbon (SOC) and soil nitrogen stocks of Teshekpuk Lake Special Area. The calculated average of SOC, soil nitrogen and ground ice in the upper 0 to 0.30 m amounts to 13.98 kg C/m², 0.82 kg N/m² and of 165.8 kg ice/m², respectively. On average the upper meter contains 42.2 kg C/m², 2.46 kg N/m² and 625.7 kg ice/m². In a depth between 0 and 2 m SOC content amounts of 48.9 kg C/m², soil nitrogen content is 3.12 kg N/m² and ground ice content amounts of 1279.6 kg ice/m². Further research in the arctic regions is needed to reduce uncertainties in soil organic carbon estimations, for example by investigations of previously poorly studied areas, by enhancing understanding of how small scale landscape heterogeneities affect soil carbon storage, and by using more realistic upscaling methods driven by well characterized landscape units. Field data such as provided in this thesis are needed to parameterize and build more reliable models and to calculate more robust future projections of climate change feedbacks with thawing permafrost.

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Jock, S. (2016): Cryolithological and biogeochemical characteristics of the upper permafrost in the Teshekpuk Lake Special Area based on permafrost cores , Master thesis, University of Potsdam.

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