Description: Ice rich Yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected Yedoma landscapes - on Sobo-Sise Island and on Bykovsky Peninsula in the North of East Siberia. Soil cores up to three meters depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from five-meter resolution, multispectral RapidEye satellite imagery. Mean landscape C and N storage in the first meter of soil for Sobo-Sise Island is estimated to be 20.2 kg C/m**-2 and 1.8 kg N/m**-2 and for Bykovsky Peninsula 25.9 kg C/m**-2 and 2.2 kg N/m**-2. Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holocene aged cover layers which can reach up to two meters on top of intact Yedoma landforms. Reconstructed sedimentation rates of 0.10 mm/yr - 0.57 mm/yr suggest sustained mineral soil accumulation across all investigated landforms. Both Yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). We further estimate that an active layer deepening by about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by ~5.8 Tg (13.2 kg C/m**-2). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich Yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates.

Description: Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits are still poorly quantified. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ~52 ka. We show that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt%).We found that the OM quality, which we define as the intrinsic potential to further transformation, decomposition, and mineralization, is also high as inferred by the lipid biomarker inventory. The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal kyr BP) and is overlaid by Last Glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso and anteiso-branched FAs relative to long chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits, suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C / N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease of HPFA values downwards along the profile probably indicates a relatively stronger OM decomposition in the oldest (MIS 3) deposits of the cliff.

Description: These data originate from 11 soil profiles sampled in northern Finland in September 2020 as part of the PeCHEc project. 8 sites were sampled on the Kutuharjue Field Research Station, a reindeer research station run by the Reindeer Herders' Association of Finland. Additional 3 sites were collected in the area around the station in the Muotkatunturi reindeer herding district as reference sites for the different landscape types found. In total, 5 sites with mineral soil (profiles with fixed volume cylinders) and 6 sites with peat (peat corer) were sampled in tundra, grassland and birch forest landscapes, covering a range of 5 different reindeer grazing intensities: a) exclosure site with no grazing (intensity 1), b) occassional migration route (intensity 2), c) regular migration route (intensity 3), d) frequent migration route (intensity 4), e) pasture (intensity 5). Analysis took place at the facilities of AWI between October 2020 and August 2021. All samples taken from the cores were analyzed for water content, bulk density, TOC, TN and δ13C. Additional radiocarbon measurements were done for selected samples of all sites. For mineral soil samples, both from mineral soil sites as well as from the bottom of the peat cores, grain size composition was determined. TC and TN were measured at AWI Potsdam CARLA Laboratory using a vario EL III Element Analyzer. TOC was measured at the same laboratory using a varioMAX C Element Analyzer. δ13C was measured at AWI Potsdam Stable Isotope Laboratory using a Delta V Advantage Isotope Ratio MS supplement equipped with a Flash 2000 Organic Elemental Analyzer. Grain size composition was determined using a Malvern Mastersizer 3000 equipped with a Malvern Hydro LV wet-sample dispersion unit. Statistics were calculated for this using Gradistat 8.0. Radiocarbon dating was carried out using the Mini Carbon Dating System (MICADAS) at AWI Bremerhaven.

Description: The data sets were made during the summer 2021, with samples collected from three cores, at two depths (active and permafrost layers). In total, six samples (3 replicates by samples) were incubated for 67 days at two temperatures (4°C and 20°C). Core sampling were performed during the joint Russian-German LENA 2018 expedition. The data sets were both collected at Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research and GeoForschungsZentrum Helmholtz-Zentrum, Potsdam, Germany. The aim of this study was to understand and quantify how much carbon may be lost during short-term permafrost thaw across different landscape units at the example of study area in the Lena Delta, Siberia. The study measures greenhouse gases (GHG) emissions based on an incubation experiment and focuses on relationships between GHG emissions and microbial abundance shifts during short-term permafrost thaw under anaerobic conditions. The objectives of the study were to: (1) Quantify CH4 and CO2 production during a short-term anaerobic incubation; (2) Establish relationships between CH4 and CO2 production and microbes (methanogens and methanotrophs); (3) and to identify settings and controls that drive gas production rates in thawed permafrost soils.

Description: This file presents the detailed description of two deep permafrost cores from the Yukechi Alas landscape in Central Yakutia, Russia. These data were recorded during subsampling of the cores and are based on visual and haptic impression. The core "Alas1" represents an adjacent alas deposit. Core was obtained during field work in March 2015.