Monitoring of Thermokarst Lake Changes and Coastal Dynamics in Permafrost Landscapes of the East Siberian Sea Region Using High Resolution Imagery and DEM Data

The coastal region bordering the East-Siberian Sea is covered by ice-rich Yedoma deposits, which are extremely vulnerable to thaw in the course of climate warming in the high latitudes. Widespread permafrost degradation throughout the Arctic resulted in relief changes on ground-ice-cored Yedoma uplands. In order to track dynamics of these processes in the Kolyma lowland tundra at Cape Maly Chukochy (N 72.08°, E 159.9°), we used a set of very high resolution remote sensing imagery (GeoEye and historical airphotos) which were compared with DEM data (TanDEM-X and derived from WorldView-2). Analysis of meteorological data have put observed changes into the context of warming and wetting trends. Yedoma uplands represent flat bogged areas featuring a high number of thermokarst ponds with an average size of 5-10 in diameter. Our image dataset revealed a doubling in the number and areal coverage of ponds from 1972 to 2009 and a further twofold increase until 2013, while thermokarst lakes that formed within Yedoma deposits increased by 7-10 %, being partially in agreement with studies conducted elsewhere in the Arctic. Coastal erosion rates from 1972 until 2013 were high and 1,5 m per year on average. We used the areal extend of thermokarst mounds (baydzherakhs) on Yedoma slopes as indicator for ground ice melt and our estimates show a baydzherakhs coverage increase of 20 % by 2013. All these changes highlight the activation and acceleration of permafrost degradation on Yedoma uplands in response to increasing air temperatures and precipitation in the East-Siberian Sea coastal region

Elevation Change Detection for Quantification of Extensive Permafrost Thaw Subsidence in East Siberian Coastal Lowlands

Permanently frozen ground in the Arctic is being destabilized by continuing permafrost degradation, an indicator of climate change in the northern high latitudes. Accelerated coastal erosion due to sea ice reduction and an increased intensity of ground settlement through ground ice melt caused by rising summer air temperatures result in widespread geomorphological activity. The objective of our study is to analyze time series of repeat terrestrial laser scanning (rLiDAR) for quantification of extensive land surface lowering through thaw subsidence, which is the main unknown in terms of recent landscape development in the vast but neglected coastal lowlands of the East Siberian Arctic. These in-situ data provide the basis for calibration and validation of large scale surface change assessments using very high resolution space-borne elevation data with high precision. Complementing our surveys, we conducted botanical mapping. This allows us to relate elevation differences to specific surface conditions and enhances our capabilities to extrapolate our local observations to larger areas through land-cover classifications of multispectral remote sensing data such as Sentinel-2. Additionally, highly detailed digital elevation models (DEMs) with sub-metre accuracy have been photogrammetrically derived from satellite stereo data. These DEMs contain valuable terrain height information for 3D change detection, in case of DEMs representing the state of a study area at different points in time. The results show that elevation differences are almost always negative. When calculated as rates over time, land surface lowering in the ground-ice-rich Siberian coastal lowlands permafrost amounts to 3-10 cm per year

A pan-Arctic initiative on the spatial and temporal dynamics of Arctic coasts

Permafrost coasts make up roughly one third of all coasts worldwide. Their erosion leads to the release of previously locked organic carbon, changes in ecosystems and the destruction of cultural heritage, infrastructure and whole communities. Since rapid environmental changes lead to an intensification of Arctic coastal dynamics, it is of great importance to adequately quantify current and future coastal changes. However, the remoteness of the Arctic and scarcity of data limit our understanding of coastal dynamics at a pan-Arctic scale and prohibit us from getting a complete picture of the diversity of impacts on the human and natural environment. In a joint effort of the EU project NUNATARYUK and the NSF project PerCS-Net, we seek to close this knowledge gap by collecting and analyzing all accessible high-resolution shoreline position data for the Arctic coastline. These datasets include geographical coordinates combined with coastal positions derived from archived data, surveying data, air and space born remote sensing products, or LiDAR products. The compilation of this unique dataset will enable us to reach unprecedented data coverage and will allow us a first insight into the magnitude and trends of shoreline changes on a pan-Arctic scale with locally highly resolved temporal and spatial changes in shoreline dynamics. By comparing consistently derived shoreline change data from all over the Arctic we expect that the trajectory of coastal change in the Arctic becomes evident. A synthesis of some initial results will be presented in the 2020 Arctic Report Card on Arctic Coastal Dynamics. This initiative is an ongoing effort – new data contributions are welcome

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

Ground-Based Measurements and High Resolution Remote Sensing of Permafrost Thaw Subsidence on Yedoma Uplands in the Lena Delta Region

Ground-ice rich terrain in the East Siberian coastal lowlands is being destabilized by continuing permafrost degradation. This degradation includes not only warming of cold permafrost, but also its thawing with consequences for local hydrology, ecosystems, biogeochemical cycling, and sometimes communities. However, thaw-associated mobilization of soil organic carbon and associated release of methane or carbon dioxide as well as relative sea level rise due to terrain subsidence of vast coastal hinterlands has potential regional to global impacts. Regarding land surface elevation of ground-ice-rich terrain, questions remain over whether the absolute surface level returns back to its initial state after a complete annual thaw-freeze cycle or if irreversible loss of ground ice occurred due to active layer deepening, leading to subsidence. Within drained thaw lake basins or areas of current thermokarst activity on yedoma uplands, seasonal thaw-freeze mechanisms proceed simultaneously with long-term geomorphic processes of land surface lowering. Now there are initial indications that ground ice in permafrost is thawing in response to rising temperatures in the Arctic, however, still only few observations of widespread and irreversible thaw subsidence exist. Permanent subsidence depends on topographic gradients enabling effective removal of ground ice melt water. Readjustment of drainage systems due to a landward advancing coastline or thermokarst lake expansion or partial drainage is likely to facilitate thaw subsidence in the coastal hinterland and calls for a more comprehensive consideration. In this study, we placed our observations in the context of an alas-yedoma thermokarst landscape that has already undergone considerable permafrost degradation in the past. Our work aims at finding commonalities and differences of change or no change on uplands, slopes, and thaw depressions on the landscape scale using multi-temporal DEMs from historical aerial photographies and modern very high resolution satellite imagery such as WorldView and GeoEye. In summer 2014 we established several long-term survey grids with geodetic benchmarks on Sobo-Sise island in the eastern Lena Delta and on the Bykovsky Peninsula in North Siberia. Initial ground-based measurements were used to create and evaluate multiple digital elevation models (DEMs) produced with satellite image stereophotogrammetry. The datasets will be used to identify inter-annual trends. Annual repeat ground measurements starting in 2015, relying on our small grid of fiber glass pipes anchored in the permafrost down to 2m depth, will provide information on spatio-temporal variations of local elevation changes in polygonal tundra

Permafrost region disturbances in space and time: a pan-arctic perspective

The permafrost region is warming at an unprecedented pace. Changing climate increases the vulnerability of permafrost. Borehole observations and ground temperature modelling across the permafrost zone indicate a global rise in permafrost temperatures. Feedback mechanisms in a warming Arctic, such as increases in wildfires, sea-ice loss or infrastructure development will further contribute to permafrost destabilization on various scales. So far, observations of permafrost region disturbances (PRD) typically focus on regional scales and holistic, pan-arctic observations are lacking. Here we present the current advances of a pan-arctic analysis of rapid permafrost landscape dynamics from 2000-2020 based on globally available satellite data (Landsat, Sentinel-2) and machine-learning methods. We expand upon previous continental-scale studies towards a pan-arctic detection and mapping of typical PRD. We analyze the spatial distribution and dynamics of lakes, wildfires and retrogressive thaw slumps (RTS) across the entire pan-arctic permafrost region. Preliminary results reveal that each PRD type has typical occurrence hot-spots. RTS are often found in regions with preserved buried glacier ice. Lake dynamics are most pronounced in ice-rich permafrost terrains along the margin of continuous permafrost. Wildfires are most dominant in arid, boreal regions. Long-term dynamics are superimposed by short-term weather conditions, such as heatwaves and precipitation events, which recently have been shown to trigger or enhance disturbances significantly. The analysis of current disturbance hot-spots and the understanding of PRD dynamics and trajectories will enhance quantifying carbon fluxes and projecting future landscape dynamics. Rapidly growing streams of remote sensing data with high spatial and temporal resolution together with new Artificial-Intelligence techniques will help to improve the monitoring of PRD across the entire pan-arctic with more detail and higher accuracy

Spatial heterogeneity and environmental predictors of permafrost region soil organic carbon stocks

Large stocks of soil organic carbon (SOC) have accumulated in the northern hemisphere permafrost region, but their current mounts and future fate remain uncertain. By analyzing an unprecedented dataset combining >2,700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated 1014−175+194 Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide the first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate