Thermokarst lake monitoring on the Bykovsky Peninsula using high-resolution remote sensing data

Thermokarst lakes are a characteristic element of arctic permafrost regions and an indicator for their rapid landscape changes. Assessing their dynamics contributes to the understanding of driving processes of change, to the evaluation of impacts on landscape characteristics as well as to the estimation of the impact on the permafrost-related carbon budget. Monitoring thermokarst lake dynamics on the Bykovsky Peninsula, consisting of ice-rich Yedoma deposits, using high resolution remote sensing imagery from 1951 to 2016, revealed a long-term tendency towards lake drainage. Approximately 17% of the 1951 lake area was lost due to coastal erosion or the development of drainage networks. In parallel, coastal erosion driven land loss amounts to 2.3% of the peninsula. We find process interconnections between coastal erosion and lake change, as well as lake change dependency on land elevation in a developed alas-yedoma thermokarst relief

Molecular biomarkers in Batagay megaslump permafrost deposits reveal clear differences in organic matter preservation between glacial and interglacial periods

The Batagay megaslump, a permafrost thaw feature in north-eastern Siberia, provides access to ancient permafrost up to ∼650 kyr old. We aimed to assess the permafrost-locked organic matter (OM) quality and to deduce palaeo-environmental information on glacial–interglacial timescales. We sampled five stratigraphic units exposed on the 55 m high slump headwall and analysed lipid biomarkers (alkanes, fatty acids and alcohols). Our findings revealed similar biogeochemical signatures for the glacial periods: the lower ice complex (Marine Isotope Stage (MIS) 16 or earlier), the lower sand unit (sometime between MIS 16–6) and the upper ice complex (MIS 4–2). The OM in these units has a terrestrial character, and microbial activity was likely limited. Contrarily, the n-alkane and fatty acid distributions differed for the units from interglacial periods: the woody layer (MIS 5), separating the lower sand unit and the upper ice complex, and the Holocene cover (MIS 1), on top of the upper ice complex. The woody layer, marking a permafrost degradation disconformity, contained markers of terrestrial origin (sterols) and high microbial decomposition (iso- and anteiso-fatty acids). In the Holocene cover, biomarkers pointed to wet depositional conditions and we identified branched and cyclic alkanes, which are likely of microbial origin. Higher OM decomposition characterised the interglacial periods. As climate warming will continue permafrost degradation in the Batagay megaslump and in other areas, large amounts of deeply buried ancient OM with variable composition and degradability are mobilised, likely significantly enhancing greenhouse gas emissions from permafrost regions

The Yedoma cliff of Sobo Sise Island, eastern Lena Delta - insights into past and modern permafrost dynamics and related organic matter stock and release

The Lena Delta in eastern Siberia is the largest Arctic delta. Its terrestrial surface is shaped by four geomorphologic units. The oldest unit is built of remnants of late Pleistocene Yedoma Ice Complex (IC) and its degradation features. The studied Yedoma cliff on Sobo Sise Island in the South-Eastern part of the delta ranges from the river level to about 28 m height and is about 1.7 km long. During a field campaign in 2018, the entire permafrost sequence of the Sobo Sise Yedoma cliff has been sampled in 0.5-m vertical intervals. The geochronological record of the Sobo Sise Yedoma spans the last 52 ka cal BP based on radiocarbon dating and age-height modelling. The sequence differentiates into three cryostratigraphic units that are MIS3 Yedoma IC (52–28 ka cal BP), MIS2 Yedoma IC (28–15 ka cal BP) and MIS1 Holocene cover (7–0 ka cal BP). The cryostratigraphic sequence is not continuous, but has chronological gaps at 36–32.5 ka cal BP, at 20.5–18 ka cal BP and at 12.5–9 cal ka BP. These gaps represent traces of past changes in permafrost deposition and/or erosion regimes and climatic conditions. The cryostratigraphic units of the Yedoma cliff are characterized by differing properties of their clastic, organic and ice components. All units are built of poorly sorted sandy silt but differ in prevalent grain-size fractions ranging from fine silt to middle sand. The organic matter (OM) content is highest in the thin MIS1 Holocene cover (TOC of 11.3±9.9 wt%, TN of 0.6±0.3 wt%), but still substantial in MIS3 Yedoma IC (TOC of 4.5±2.5 wt%, TN of 0.3±0.1 wt%) and in MIS2 Yedoma IC (TOC of 2.1±1.3 wt%, TN of 0.2±0.1 wt%). The presence of syngenetic ice wedges in all units and the high content of intrasedimentary ice amount to a total volumetric ice content of 88.4 vol%. The high ice content in combination with the exposition of the cliff towards the main river channel results in a very high susceptibility to thaw and thermo-erosion. The high mean cliff erosion rate of 10.3 m yr−1 (1975-2018) results in large OM quantities entering the Lena River (3.2±2.1 kt organic carbon per year, 0.3±0.1 kt nitrogen per year along the 1.7 km long Yedoma cliff). Ongoing fluvial dynamics and changing runoff regimes with extended ice-free seasons and warmer water will most likely maintain high permafrost cliff erosion rates in the future and further facilitate high fluxes of terrestrial fossil OM into the riverine and eventually marine ecosystems

The Yedoma cliff of Sobo Sise Island - insights into past and modern permafrost dynamics and related organic matter stock and release

The present study of the permafrost exposed the Sobo-Sise Yedoma cliff in the eastern Lena Delta provides a comprehensive cryostratigraphic and organic matter (OM) inventory, insights into permafrost aggradation and degradation over the last about 52 thousand years and their climatic and morphodynamic controls on regional scale of the Central Laptev Sea coastal region in NE Siberia

Morphodynamic Types of the Laptev Sea Coast: A Review

The Laptev Sea coast has a unique high-latitude and dynamic landscape. The presence of low-temperature permafrost (below −7 °C) and its high ice content (up to 90%) determine a wide array of permafrost landforms and features. Under the actions of thermal abrasion and thermal denudation, high rates of coastal retreat are evident within this region. Local differences in the geological structure and sea hydrodynamic conditions determine the diversity of this sea coast’s types. In this review, we present the results of a morphodynamic classification and segmentation of the Laptev Sea coast. The integrated approach used in the classification took into account the leading relief-forming processes that act upon this coastal zone. The research scale of 1:100,000 made it possible to identify and characterize the morphologies of the coast and their spatial distributions within the study area. The presented original classification can be considered to be universal for the eastern Arctic seas of Eurasia; it may be used as a basis for further scientific and applied research

Coastal dynamics of the Kolguev Island

Kolguev Island is the most western point in the Russian Arctic with tabular ground ice occurrence. Since the Barents Sea is characterized by strong sea ice decline, it is very interesting to study coastal dynamics in conjunction with cryogenic processes in this region. Ice exposures on coastal bluffs favor the activation of thermal abrasion and thermal denudation. Headwall retreat of retrogressive thaw slumps causes not only thermocirque formation, but also leads to increasing coastal destruction rates. This study on Kolguev Island continues and expands our earlier research efforts on coastal dynamics in the region. As a result of field and remote sensing data analysis, coastline classification and segmentation were done according to the morphodynamics principle. The following types are defined: 1) thermo-abrasion wave exposed cliffs, 2) abrasion (thermo-abrasion) with stabilized cliffs, bordered by beaches or accumulative terraces, 3) sheltered abrasion (thermo-abrasion) cliffs, 4) accumulating coasts and accumulative forms, 5) accumulated coasts with sheltered tidal flats, 6) deltas. Thermo-abrasion cliff coasts are predominantly distributed in the west, north and northeast of the island, and accumulative shores in the south, southeast and east of the island. New data on thermal denudation and thermal abrasion rates for Kolguev Island have been obtained using a whole set of multi-temporal satellite images of high and very-high spatial resolution (GeoEye, WorldView, Alos Prism, SPOT, Formosat, RapidEye and Kompsat) covering the period from 2002 to 2017. For image orthorectification purposes, the 12 m TanDEM-X DEM has been used. However, since the TanDEM-X DEM is based on averaged bistatic SAR surveys acquired during the period 2010–2012. This DEM can be used only for orthorectification of images newer than 2012 to determine the exact coastal bluff position and thermocirque edges. We therefore reconstructed the relief along erosive coastline segments by modifying the initial TanDEM-X DEM through extrapolation of coastal bluff edge elevations and restoration of the coastal plain relief at 200–300 m towards the sea for orthorectification of images prior to 2012. All raw images were terrain-corrected and georeferenced using a comprehensive block adjustment, resulting in a very high absolute and relative accuracy of all images. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year. Within key-sites that included three large thermocirques maximum headwall retreat rates were 1.9-15.1 m/year for 2002-2012 and 2.2-13.5 m/year for 2012-2017 yrs. In comparison, activation of thermo-denudation has been also noted along the Kara Sea coast where rates raised up to 13 m/year and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years. Accumulative forms in the southern part of Kolguev Island are also being eroded. Thus, on Vostochnye Ploskie Koshki (on the south of the island), the retreat of formerly accumulative coasts from 2009 to 2016 in some areas amounted up to 62 m. This study was supported by RFBR grants № 18-05-60080 (coastal destruction rates estimation), 18-05-60221 (method of satellite images orthorectification, based on reconstructed DEM), ERC grant #338335 PETA-CARB, and German Academic Exchange Service (DAAD) with funds from BMBF and EU FP7, grant #605728

Analyzing tundra vegetation characteristics for enhancing terrestrial LiDAR surveys of permafrost thaw subsidence on yedoma uplands

Surface subsidence is a widespread phenomenon in Arctic lowlands characterized by permafrost deposits. Together with active layer thickness dynamics surface subsidence is an important indicator of permafrost degradation in climate warming conditions. Due to small changes of surface heights of several centimeters or less per year, high-resolution and high-accuracy data are necessary to detect thaw subsidence dynamics in tundra lowlands. An appropriate method to receive such data is repeat terrestrial laser scanning (LiDAR). However, for LiDAR data analysis, uncertainties connected with vegetation dynamics should be taken into account. The vegetation type and its succession reflect the microrelief features, resulting in an areal differentiation of surface heights changes. Depending on wetness, possible influences might result from moss-lichen cover and its thickness dynamics. In this study we present some results of the vegetation characteristics and dynamics in context of its impact on the terrestrial LiDAR investigations for thaw subsidence assessment on yedoma uplands. During expeditions to the Lena Delta and the Bykovsky Peninsula in Northern Yakutia in 2015-2016, repeat terrestrial laser scanning was conducted on yedoma uplands formed by very ice-rich Yedoma Ice Complex deposits. On the Bykovsky Peninsula, detailed vegetation descriptions of the main vegetation types were done including all species projective cover, cotton grass tussocks height and area sizes, moss-lichen thickness and ALT measurements. Subsidence was about 3.5 cm on average and is mostly observed on drained inclined sites with dwarf-shrub graminoid, cotton-grass, moss-lichen tundra, representing initial baydzherakhs (thermokarst mounds). Surface heave is observed mainly within bogged depressions with sedge, moss tundra. The average ALT was 39±4.1 cm and 32±5.6 cm in 2015 and 2016, respectively. However, the ALT significantly varies locally and depends on the vegetation type and species. Cotton grass leaves average length decreased from 14.4 in 2015 to 12.9 as well as tussock area size (0.32 m2 in 2015, and 0.13 m2 in 2016). This data can be used for the interpretation of LiDAR data for sites with cotton grass prevalence. Less deep ALT and cotton grass size in 2016 indicate that climate conditions were less favorable for seasonal subsidence development in 2016. The sum of positive daily air temperatures was almost in the same order of magnitude in 2016 as in 2015 for the period until end of August (636 degree days in 2015 and 628 degree days in 2016). However, interannual surface subsidence was progressing, indicating a decreased resistivity of yedoma uplands in terms of thaw subsidence under current, generally warmer conditions. The thickness of the moss-lichens layer in average is about 5 cm for the live part and 12 cm for both live and non-live parts. The lab drying in the 20°С conditions shows the decrease of moss-lichens layer samples thickness from 12,4 to 11,8 cm in average. The changes of moss-lichens thickness could be ignored as drying resulted in small changes it is very unlikely to have such drying in really tundra conditions Our results show the importance of considering vegetation and their dynamics for the interpretation of repeat terrestrial LiDAR data for thaw subsidence estimation