ALBERT

Description: This data set includes the data for the publication Fuchs et al. (2019), Organic carbon and nitrogen stocks along a thermokarst lake sequence in Arctic Alaska, doi:10.1029/2018JG004591. Impacts of successive thermokarst lake stages on soil organic carbon and nitrogen storage, Arctic Alaska. This study combines terrestrial and lacustrine cores to a depth of two meters for a carbon and nitrogen stock estimation in a heavily thermokarst affected study region as well as describes the landscape chronology of the study area which is characterized by multiple drained thermokarst lake basins of different generations. The first data set (doi:10.1594/PANGAEA.895163) includes the raw laboratory data (TOC, TC, TN, C/N) from the permafrost cores collected at the Teshekpuk Lake Area. The data for the lacustrine cores are published on Pangaea and accessible with the link: https://doi.org/10.1594/PANGAEA.864814 (Lenz et al., 2016). All laboratory analyses on the terrestrial cores were carried out at the Alfred Wegener Institute Potsdam. The second data set (doi:10.1594/PANGAEA.895165) presents the carbon (in kg C m-2) and nitrogen (in kg N m-2) stocks for all the collected cores for the reference depths 0-30 cm, 0-100 cm, 0-150 cm, 0-200 cm. This includes terrestrial as well as lacustrine cores. The third data set (doi:10.1594/PANGAEA.895166) includes 19 radiocarbon dates from five different permafrost cores. The samples were analyzed at the Radiocarbon Laboratory in Poznan, Poland with the accelerated mass spectrometry (AMS) dating method (Goslar et al., 2004). In addition to the AMS dates, the radiocarbon dates were calibrated with the Calib 7.1 software into calibrated years before present and organic carbon accumulation rates were calculated for each of the cores (Stuiver & Reimer, 1993; Stuiver et al., 2017). In addition, a shapefile (Landforms_Teshekpuk_Area) is available including drained thermokarst lake basins of different lake stages, thermokarst lakes (〉1 ha), primary surfaces and drainage channels. This landform classification was used in the original study to characterize the chronology of the landscape as well as to calculate landscape carbon and nitrogen stocks.

Description: Thermokarst lake landscapes are permafrost regions, which are prone to rapid (on seasonal to decadal timescales) changes, affecting carbon and nitrogen cycles. However, there is a high degree of uncertainty related to the balance between carbon and nitrogen cycling and storage. We collected twelve permafrost soil cores from six drained thermokarst lake basins (DTLB) along a chronosequence north of Teshekpuk Lake in northern Alaska, and analyzed them for carbon and nitrogen contents. For comparison, we included three lacustrine cores from an adjacent thermokarst lake and one soil core from a non‐thermokarst affected remnant upland. This allowed to calculate the carbon and nitrogen stocks of the three primary landscape units (DTLB, lake, and upland), to reconstruct the landscape history, and to analyze the effect of thermokarst lake formation and drainage on carbon and nitrogen stocks. We show that carbon and nitrogen contents and the carbon‐nitrogen ratio are considerably lower in sediments of extant lakes than in the DTLB or upland cores indicating degradation of carbon during thermokarst lake formation. However, we found similar amounts of total carbon and nitrogen stocks due to the higher density of lacustrine sediments caused by the lack of ground‐ice compared to DTLB sediments. In addition, the radiocarbon‐based landscape chronology for the past 7,000 years reveals five successive lake stages of partially, spatially overlapping DTLBs in the study region, reflecting the dynamic nature of ice‐rich permafrost deposits. With this study, we highlight the importance to include these dynamic landscapes in future permafrost carbon feedback models.

Description: 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.