High-Resolution Thaw Dynamics of Two Latitudinally Distant Alaska Thermokarst Sites: A Field Study

Permafrost thaw and resultant landscape change have a net warming effect on the climate. Northern high latitudes are projected to get warmer and wetter in the future which will affect rates of permafrost thaw and the mechanisms by which thaw occurs. To better understand changing thaw dynamics, we instrumented two actively thawing permafrost features: 1) an isolated permafrost plateau in south-central Alaska with currently warm and wet climate conditions that mirror those expected in more northern permafrost regions in the future, and 2) a site in Interior Alaska that is experiencing more typical subarctic climate conditions. Thaw dynamics at the two sites were observed with a dense instrumentation network of 82 distributed temperature profilers (DTPs). Installed DTPs measured temperature every 10 cm from the soil surface into the permafrost table, which ranged from 46 cm to 220 cm below the ground surface, at a 15-minute measurement interval. These data, in addition to accompanying groundwater, meteorological, soil moisture, frost probe, and vegetation data, are explored to further define the environmental factors that contribute to permafrost thaw. One such contributing factor is the thermal impact of rain. In 2019, before installing our DTPs and soil moisture sensors, we observed rapid thaw directly following a July rain event at some sensor locations of the south-central permafrost feature. During this event, more than half of the seasonal frost (~30 cm) thawed in less than a week. If similar warm rain events occur during the 2021 summer season, we will explore the relative thermal contributions of direct advective heat transport to that of increased soil thermal conductivity after rain using our new instrumentation. Our efforts to better understand the environmental factors that lead to thaw and to determine the rates at which permafrost thaws under different climate conditions will allow for better preparation, modeling, and policymaking for the future.