Regional Patterns and Asynchronous Onset of Ice-Wedge Degradation since the Mid-20th Century in Arctic Alaska

• Published in: Remote sensing (Basel, Switzerland) Vol. 10; no. 8; p. 1312
• Main Authors: Frost, Gerald, Christopherson, Tracy, Jorgenson, M., Liljedahl, Anna, Macander, Matthew, Walker, Donald, Wells, Aaron
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-08-2018
• Subjects: 20th century; Alaska; Alluvial deposits; Alluvial plains; Arctic tundra; Climate change; Coastal plains; Environmental gradient; Foothills; geomorphology; Ground ice; Hydrology; Ice; Ice ages; ice wedge; Image resolution; Landscape; North Slope; patterned ground; Permafrost; Pits; Polygons; Ponding; Remote sensing; Soil erosion; Surface water; Taiga & tundra; Thawing; thermokarst; Vegetation; Wedges; Alaska; United States > US; Arctic region; North Slope
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs10081312

Ice-wedge polygons are widespread and conspicuous surficial expressions of ground-ice in permafrost landscapes. Thawing of ice wedges triggers differential ground subsidence, local ponding, and persistent changes to vegetation and hydrologic connectivity across the landscape. Here we characterize spatio-temporal patterns of ice-wedge degradation since circa 1950 across environmental gradients on Alaska’s North Slope. We used a spectral thresholding approach validated by field observations to map flooded thaw pits in high-resolution images from circa 1950, 1982, and 2012 for 11 study areas (1577–4460 ha). The total area of flooded pits increased since 1950 at 8 of 11 study areas (median change +3.6 ha; 130.3%). There were strong regional differences in the timing and extent of degradation; flooded pits were already extensive by 1950 on the Chukchi coastal plain (alluvial-marine deposits) and subsequent changes there indicate pit stabilization. Degradation began more recently on the central Beaufort coastal plain (eolian sand) and Arctic foothills (yedoma). Our results indicate that ice-wedge degradation in northern Alaska cannot be explained by late-20th century warmth alone. Likely mechanisms for asynchronous onset include landscape-scale differences in surficial materials and ground-ice content, regional climate gradients from west (maritime) to east (continental), and regional differences in the timing and magnitude of extreme warm summers after the Little Ice Age.