The catastrophic thermokarst lake drainage events of 2018 in northwestern Alaska: fast-forward into the future

Northwestern Alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. In particular, the Baldwin and northern Seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage like many other regions at the southern margins of continuous permafrost. We used Sentinel-1 synthetic aperture radar (SAR) and Planet CubeSat optical remote sensing data to analyze recently observed widespread lake drainage. We then used synoptic weather data, climate model outputs and lake ice growth simulations to analyze potential drivers and future pathways of lake drainage in this region. Following the warmest and wettest winter on record in 2017/2018, 192 lakes were identified as having completely or partially drained by early summer 2018, which exceeded the average drainage rate by a factor of ∼ 10 and doubled the rates of the previous extreme lake drainage years of 2005 and 2006. The combination of abundant rain- and snowfall and extremely warm mean annual air temperatures (MAATs), close to 0 ∘C, may have led to the destabilization of permafrost around the lake margins. Rapid snow melt and high amounts of excess meltwater further promoted rapid lateral breaching at lake shores and consequently sudden drainage of some of the largest lakes of the study region that have likely persisted for millennia. We hypothesize that permafrost destabilization and lake drainage will accelerate and become the dominant drivers of landscape change in this region. Recent MAATs are already within the range of the predictions by the University of Alaska Fairbanks' Scenarios Network for Alaska and Arctic Planning (UAF SNAP) ensemble climate predictions in scenario RCP6.0 for 2100. With MAAT in 2019 just below 0 ∘C at the nearby Kotzebue, Alaska, climate station, permafrost aggradation in drained lake basins will become less likely after drainage, strongly decreasing the potential for freeze-locking carbon sequestered in lake sediments, signifying a prominent regime shift in ice-rich permafrost lowland regions

Increase in beaver dams controls surface water and thermokarst dynamics in an Arctic tundra region, Baldwin Peninsula, northwestern Alaska

Beavers are starting to colonize low arctic tundra regions in Alaska and Canada, which hasimplications for surface water changes and ice-rich permafrost degradation. In this study, weassessed the spatial and temporal dynamics of beaver dam building in relation to surface waterdynamics and thermokarst landforms using sub-meter resolution satellite imagery acquiredbetween 2002 and 2019 for two tundra areas in northwestern Alaska. In a 100 km2study area nearKotzebue, the number of dams increased markedly from 2 to 98 between 2002 and 2019. In a430 km2study area encompassing the entire northern Baldwin Peninsula, the number of damsincreased from 94 to 409 between 2010 and 2019, indicating a regional trend. Correlating data onbeaver dam numbers with surface water area mapped for 12 individual years between 2002 and2019 for the Kotzebue study area showed a significant positive correlation (R2=0.61; p < .003).Beaver-influenced waterbodies accounted for two-thirds of the 8.3% increase in total surface waterareain the Kotzebue study area during the 17 year period. Beavers specifically targeted thermokarstlandforms in their dam building activities. Flooding of drained thermokarst lake basins accountedfor 68% of beaver-influenced surface water increases, damming of lake outlets accounted for 26%,and damming of beaded streams accounted for 6%. Surface water increases resulting from beaverdam building likely exacerbated permafrost degradation in the region, but dam failure alsofactored into the drainage of several thermokarst lakes in the northern Baldwin Peninsula studyregion, which could promote local permafrost aggradation in freshly exposed lake sediments. Ourfindings highlight that beaver-driven ecosystem engineering must be carefully considered whenaccounting for changes occurring in some permafrost regions, and in particular, regional surfacewater dynamics in low Arctic and Boreal landscapes

Landsat-Based Trend Analysis of Lake Dynamics across Northern Permafrost Regions

Lakes are a ubiquitous landscape feature in northern permafrost regions. They have a strong impact on carbon, energy and water fluxes and can be quite responsive to climate change. The monitoring of lake change in northern high latitudes, at a sufficiently accurate spatial and temporal resolution, is crucial for understanding the underlying processes driving lake change. To date, lake change studies in permafrost regions were based on a variety of different sources, image acquisition periods and single snapshots, and localized analysis, which hinders the comparison of different regions. Here, we present a methodology based on machine-learning based classification of robust trends of multi-spectral indices of Landsat data (TM, ETM+, OLI) and object-based lake detection, to analyze and compare the individual, local and regional lake dynamics of four different study sites (Alaska North Slope, Western Alaska, Central Yakutia, Kolyma Lowland) in the northern permafrost zone from 1999 to 2014. Regional patterns of lake area change on the Alaska North Slope (−0.69%), Western Alaska (−2.82%), and Kolyma Lowland (−0.51%) largely include increases due to thermokarst lake expansion, but more dominant lake area losses due to catastrophic lake drainage events. In contrast, Central Yakutia showed a remarkable increase in lake area of 48.48%, likely resulting from warmer and wetter climate conditions over the latter half of the study period. Within all study regions, variability in lake dynamics was associated with differences in permafrost characteristics, landscape position (i.e., upland vs. lowland), and surface geology. With the global availability of Landsat data and a consistent methodology for processing the input data derived from robust trends of multi-spectral indices, we demonstrate a transferability, scalability and consistency of lake change analysis within the northern permafrost region

From Images to Hydrologic Networks - Understanding the Arctic Landscape with Graphs

Remote sensing-based Earth Observation plays an important role in assessing environmental changes throughout our planet. As an image-heavy domain, the evaluation of the data strongly focuses on statistical and pixel-based spatial analysis methods. However, considering the complexity of our Earth system, there are some environmental structures and dependencies that are not possible to accurately describe with these traditional image analysis approaches. One example for such a limitation is the representation of (spatial) networks and their characteristics. In this study, we thus propose a computer vision approach that enables the representation of semantic information gained from images as graphs. As an example, we investigate digital terrain models of Arctic permafrost landscapes with its very characteristic polygonal patterned ground. These regular patterns, which are clearly visible in high-resolution image and elevation data, are formed by subsurface ice bodies that are very vulnerable to rising temperatures in a warming Arctic. Observing these networks’ topologies and metrics in space and time with graph analysis thus allows insights into the landscape’s complex geomorphology, hydrology, and ecology and therefore helps to quantify how they interact with climate change. We show that results extracted with this analytical and highly automated approach are in line with those gathered from other manual studies or from manual validation. Thus, with this approach, we introduce a method that, for the first time, enables upscaling of such terrain and network analysis to potentially pan-Arctic scales where collecting in-situ field data is strongly limited

Soil carbon and nitrogen stocks in Arctic river deltas: New data for three Northwest Alaskan deltas

Arctic river deltas are dynamic and rapidly changing permafrost environments in a warming Arctic. Our study presents new data on permafrost carbon and nitrogen stocks from 26 soil permafrost cores collected from the Noatak, Kobuk and Selawik river deltas in Western Alaska. We analyzed 318 samples for total carbon (TC) and total nitrogen (TN). Average landscape-scale carbon storage is 50.1 ± 7.8 kg C (both organic and inorganic) and 2.4 ± 0.3 kg N m-2 (0-200 cm). This totals 67 ± 11 Mt C and 3.3 ± 0.6 Mt N in the first two meters of soil in the Noatak, Kobuk and Selawik deltas combined. Our findings demonstrate that Arctic river deltas are important regions of permafrost soil carbon storage and need to be considered in panarctic permafrost carbon estimations

Tundra be dammed: Beaver colonization of the Arctic

Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293 km2) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following overtrapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic