Recent degradation of Interior Alaska permafrost mapped with ground surveys, geophysics, deep drilling, and repeat airborne LiDAR

• Main Authors: Douglas, Thomas A., Hiemstra, Christopher A., Anderson, John E., Barbato, Robyn A., Bjella, Kevin L., Deeb, Elias J., Gelvin, Arthur B., Nelsen, Patricia E., Newman, Stephen D., Saari, Stephanie P., Wagner, Anna M.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; Fairbanks; Talik; Ice; permafrost; Subarctic; Thermokarst; Tundra; Alaska
• Online Access: https://doi.org/10.5194/tc-2021-47; https://tc.copernicus.org/preprints/tc-2021-47/

Permafrost underlies one quarter of the northern hemisphere but is at increasing risk of thaw from climate warming. Recent studies across the Arctic have identified areas of rapid permafrost degradation from both top-down and lateral thaw. Of particular concern is thawing of ice rich high carbon content syngenetic <q>yedoma</q> permafrost like much of the permafrost in the region around Fairbanks, Alaska. With a mean annual temperature of −2 °C subtle differences in ecotype and permafrost ice and soil content control the near-surface permafrost thermal regime. Long-term measurements of the seasonally thawed <q>active layer</q> across central Alaska have identified an increase in permafrost thaw degradation that is expected to continue, and even accelerate, in coming decades. A major knowledge gap is relating belowground measurements of seasonal thaw, permafrost characteristics, and talik development with aboveground ecotype properties and thermokarst expansion that can readily quantify vegetation cover and track surface elevation changes over time. This study was conducted from 2013–2020 along four 400 to 500 m long transects near Fairbanks, Alaska. Repeat end of season active layer depths, near-surface permafrost temperature measurements, electrical resistivity tomography (ERT), deep (> 5 m) boreholes, and repeat airborne LiDAR were used to measure top down thaw and map thermokarst development at the sites. Our study confirms previous work using ERT to map surface thawed zones, however, our deep boreholes confirm the boundaries between frozen and thawed zones that are needed to model top down, lateral, and bottom-up thaw. At disturbed sites seasonal thaw increased up to 25 % between mid-August and early October and suggests active layer depths must be made as late in the fall season as possible because the projected increase in the summer season of just a few weeks could lead to significant additional thaw. At our sites, tussock tundra and spruce forest are associated with the lowest mean annual near-surface permafrost temperatures while mixed forest ecotypes are the warmest and exhibit the highest degree of recent temperature warming and thaw degradation. Thermokarst features and perennially thawed zones (taliks) have been identified at all sites. Our measurements, when combined with longer-term records from yedoma across the 500,000 km 2 area of central Alaska show widespread initiation of near-surface permafrost thaw since roughly 2010. Using this partial area of the yedoma domain and projecting our thaw depth increases, by ecotype, across this domain we calculate 0.44 Gt of permafrost soil C have been thawed over the 7 year period, an amount equal to the yearly CO 2 emissions of Australia. Since the yedoma permafrost and the variety of ecotypes at our sites represent much of the Arctic and subarctic land cover this study shows remote sensing measurements, top-down and bottom-up thermal modelling, and ground based surveys can be used predictively to identify areas of highest risk for permafrost thaw from projected future climate warming.