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

• Published in: Remote Sensing
• Main Authors: Gerald V. Frost, Tracy Christopherson, M. Torre Jorgenson, Anna K. Liljedahl, Matthew J. Macander, Donald A. Walker, Aaron F. Wells
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2018
• Subjects: permafrost; ice wedge; patterned ground; thermokarst; geomorphology; Arctic tundra; climate change; North Slope; Alaska; Science; Q; Arctic; Chukchi; Climate change; Ice; north slope; Thermokarst; Tundra; wedge*
• Online Access: https://doi.org/10.3390/rs10081312; https://doaj.org/article/5ab69278b8d142a0ab182754dcbc53e3

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.