Recent degradation of interior Alaska permafrost mapped with ground surveys, geophysics, deep drilling, and repeat airborne lidar
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. 
Published: August 2021

Abstract. 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 syngenetic “yedoma” permafrost which is ice-rich and has a high
carbon content. This type of permafrost is common in the region around Fairbanks, Alaska, and across central Alaska expanding westward to the Seward Peninsula. A major knowledge gap is relating belowground measurements of seasonal thaw, permafrost characteristics, and residual thaw layer 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 to 2020 along
four 400 to 500 m long transects near Fairbanks, Alaska. Repeat active layer depths, near-surface permafrost temperature measurements, electrical
resistivity tomography (ERT), deep (> 5 m) boreholes, and repeat
airborne light detection and ranging (lidar) were used to measure top-down
permafrost 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 measurements to evaluate active layer depth 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,
residual thaw layers, and taliks have been identified at all sites. Our
measurements, when combined with longer-term records from yedoma across the
500 000 km2 area of central Alaska, show widespread near-surface
permafrost thaw since 2010. Projecting our thaw depth increases, by ecotype,
across the yedoma domain, we calculate a first-order estimate that 0.44 Pg of organic carbon in permafrost soil has thawed over the past 7 years, which,
for perspective, is an amount of carbon nearly equal to the yearly CO2
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 modeling, and ground-based surveys can be used predictively to identify areas of the highest risk for permafrost thaw from projected future climate warming.