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1. Synthetic aperture radar (SAR) detects large gas seeps in Alaska lakes

   https://doi.org/10.1088/1748-9326/ad2b2a  

   Engram, Melanie; Anthony, Katey Walter (March 2024, Environmental Research Letters)

   Abstract Reservoirs of¹⁴C-depleted methane (CH₄), a potent greenhouse gas, residing beneath permafrost are vulnerable to escape where permafrost thaw creates open-talik conduits. However, little is known about the magnitude and variability of this methane source or its response to climate change. Remote-sensing detection of large gas seeps would be useful for establishing a baseline understanding of sub-permafrost methane seepage, as well as for monitoring these seeps over time. Here we explored synthetic aperture radar’s (SAR) response to large sub-permafrost gas seeps in an interior Alaskan lake. In SAR scenes from 1992 to 2011, we observed high perennial SAR L-band backscatter (σ⁰) from a ∼90 m-wide feature in the winter ice of interior Alaska’s North Blair Lake (NBL). Spring and fall optical imagery showed holes in the ice at the same location as the SAR anomaly. Through field work we (1) confirmed gas bubbling at this location from a large pockmark in the lakebed, (2) measured flux at the location of densest bubbles (1713 ± 290 mg CH₄m⁻²d⁻¹), and (3) determined the bubbles’ methane mixing ratio (6.6%), radiocarbon age (18 470 ± 50 years BP), and δ¹³C_CH4values (−44.5 ± 0.1‰), which together may represent a mixture of sources and processes. We performed a first order comparison of SARσ⁰from the NBL seep and other known sub-permafrost methane seeps with diverse ice/water interface shapes in order to evaluate the variability of SAR signals from a variety of seep types. Results from single-polarized intensity and polarimetric L-band SAR decompositions as well as dual-polarized C-band SAR are presented with the aim to find the optimal SAR imaging parameters to detect large methane seeps in frozen lakes. Our study indicates the potential for SAR remote sensing to be used to detect and monitor large, sub-permafrost gas seeps in Arctic and sub-Arctic lakes. 

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2. Saline permafrost degradation below a shallow thermokarst lake in northern Alaska, 2008-2023

   https://doi.org/10.18739/A20P0WS3K  

   Jones, Benjamin; Kanevskiy, Mikhail; Parsekian, Andrew; Bergstedt, Helena; Ward Jones, Melissa; Rangel, Rodrigo; Hinkel, Kenneth; Shur, Yuri (January 2023, NSF Arctic Data Center)

   This dataset supports the findings of the research paper submitted to the journal Geophysical Research Letters that documents the rapid thaw of saline permafrost below a shallow thermokarst lake near Utqiagvik, Alaska. The lake, East Twin Lake, is located in the Barrow Environmental Observatory. We conducted repeat drilling-based surveys at East Twin Lake in the Barrow Environmental Observatory near Utqiagvik, Alaska between 2008 and 2023. These field data were integrated with transient electromagnetic (TEM) near-surface geophysics soundings in 2016 and 2022 and analysis of a time-series of wintertime Synthetic Aperture Radar (SAR) satellite imagery from 2015 to 2023 to assess changes in lake and sub-lake properties. Finally, we assessed the impact of thawing saline permafrost on shore erosion by quantifying a regime shift in the lateral expansion rate of East Twin Lake between 1948 and 2022. The datasets consist of a CSV file with the point measurements from the drilling campaign, processed TEM data along with the script, a table of SAR backscatter values extracted for three lakes, and a table with lake expansion rates for East Twin Lake. 

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3. Unpiloted Aerial Vehicle Retrieval of Snow Depth Over Freshwater Lake Ice Using Structure From Motion

   https://doi.org/10.3389/frsen.2021.675846  

   Gunn, Grant E.; Jones, Benjamin M.; Rangel, Rodrigo C. (July 2021, Frontiers in Remote Sensing)

   null (Ed.)

   The presence and thickness of snow overlying lake ice affects both the timing of melt and ice-free conditions, can contribute to overall ice thickness through its insulative capacity, and fosters the development of variable ice types. The use of UAVs to retrieve snow depths with high spatial resolution is necessary for the next generation of ultra-fine hydrological models, as the direct contribution of water from snow on lake ice is unknown. Such information is critical to the understanding of the physical processes of snow redistribution and capture in catchments on small lakes in the Arctic, which has been historically estimated from its relationship to terrestrial snowpack properties. In this study, we use a quad-copter UAV and SfM principles to retrieve and map snow depth at the winter maximum at high resolution over a the freshwater West Twin Lake on the Arctic Coastal Plain of northern Alaska. The accuracy of the snow depth retrievals is assessed using in-situ observations ( n = 1,044), applying corrections to account for the freeboard of floating ice. The average snow depth from in-situ observations was used calculate a correction factor based on the freeboard of the ice to retrieve snow depth from UAV acquisitions (RMSE = 0.06 and 0.07 m for two transects on the lake. The retrieved snow depth map exhibits drift structures that have height deviations with a root mean square (RMS) of 0.08 m (correlation length = 13.8 m) for a transect on the west side of the lake, and an RMS of 0.07 m (correlation length = 18.7 m) on the east. Snow drifts present on the lake also correspond to previous investigations regarding the variability of snow on lakes, with a periodicity (separation) of 20 and 16 m for the west and east side of the lake, respectively. This study represents the first retrieval of snow depth on a frozen lake surface from a UAV using photogrammetry, and promotes the potential for high-resolution snow depth retrieval on small ponds and lakes that comprise a significant portion of landcover in Arctic environments. 

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

   https://doi.org/10.5194/tc-14-4279-2020  

   Nitze, Ingmar; Cooley, Sarah W.; Duguay, Claude R.; Jones, Benjamin M.; Grosse, Guido (January 2020, The Cryosphere)

   null (Ed.)

   Abstract. Northwestern Alaska has been highly affected by changing climatic patternswith new temperature and precipitation maxima over the recent years. Inparticular, the Baldwin and northern Seward peninsulas are characterized byan abundance of thermokarst lakes that are highly dynamic and prone to lakedrainage like many other regions at the southern margins of continuouspermafrost. We used Sentinel-1 synthetic aperture radar (SAR) and PlanetCubeSat optical remote sensing data to analyze recently observed widespreadlake drainage. We then used synoptic weather data, climate model outputs andlake ice growth simulations to analyze potential drivers and future pathwaysof lake drainage in this region. Following the warmest and wettest winter onrecord in 2017/2018, 192 lakes were identified as having completely orpartially drained by early summer 2018, which exceeded the average drainagerate by a factor of ∼ 10 and doubled the rates of the previousextreme lake drainage years of 2005 and 2006. The combination of abundantrain- and snowfall and extremely warm mean annual air temperatures (MAATs),close to 0 ∘C, may have led to the destabilization of permafrostaround the lake margins. Rapid snow melt and high amounts of excessmeltwater further promoted rapid lateral breaching at lake shores andconsequently sudden drainage of some of the largest lakes of the studyregion that have likely persisted for millennia. We hypothesize that permafrostdestabilization and lake drainage will accelerate and become the dominantdrivers of landscape change in this region. Recent MAATs are already withinthe range of the predictions by the University of Alaska Fairbanks' Scenarios Network for Alaska and Arctic Planning (UAF SNAP) ensemble climate predictions inscenario 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. 

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5. Greenland Ice Sheet wide supraglacial lake evolution and dynamics: insights from the 2018 and 2019 melt seasons

   https://doi.org/10.31223/X5871P  

   Dunmire, Devon; Subramanian, Aneesh; Hossain, Emam; Gani, Md; Banwell, Alison; Younas, Hammad; Myers, Brendan (July 2024, Eartharxiv)

   Supraglacial lakes on the Greenland Ice Sheet (GrIS) can impact both the ice sheet surface mass balance and ice dynamics. Thus, understanding the evolution and dynamics of supraglacial lakes is important to provide improved parameterizations for ice sheet models to enable better projections of future GrIS changes. In this study, we utilize the growing inventory of optical and microwave satellite imagery to automatically determine the fate of Greenland-wide supraglacial lakes during 2018 and 2019; cool and warm melt seasons respectively. We develop a novel time series classification method to categorize lakes into four classes: 1) refreezing, 2) rapidly draining, 3) slowly draining, and 4) buried. Our findings reveal significant interannual variability between the two melt seasons, with a notable increase in the proportion of draining lakes in 2019. We also find that as mean lake depth increases, so does the percentage of lakes that drain, indicating that lake depth may influence hydrofracture potential. However, we also observe that non-draining lakes are deeper during the cooler 2018 melt season, suggesting that additional factors may predispose lakes to drain earlier in a warmer year. Our automatic classification approach and the resulting two-year ice-sheet-wide dataset provide unprecedented insights into GrIS supraglacial lake dynamics and evolution, offering a valuable resource for future research. 

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