Environmental Controls on Local Thaw of a Vegetation-Protected Permafrost Plateau

Authors

Joel Eklof¹*, Ben Jones², Baptiste Dafflon³, Katie Ring¹, Mark Waldrop⁴, Marie English¹, Rebecca Neumann¹

Institutions

¹University of Washington, Seattle, WA; ²University of Alaska, Fairbanks, AK; ³Lawrence Berkeley National Laboratory, Berkeley, CA; ⁴United States Geological Survey, Menlo Park, CA

Abstract

Atmospheric temperatures in the Northern Hemisphere have warmed faster than the global average, and this amplified warming is expected to strengthen in the future. Trends in permafrost temperature are consistent with trends in atmospheric temperature, with widespread observed warming. However, other environmental factors, such as ecologic, hydrologic, and topographic conditions, also regulate permafrost temperature, progression, and stability. Vegetation-protected permafrost, located in regions with a MAAT above 0°C, persist in these unfavorable climates due to favorable ecologic conditions. Understanding how this vegetation-protected permafrost degrades is crucial, because vegetation-protected permafrost acts as a forecaster and predictor of thaw in more northern latitudes.

To better understand environmental factors affecting soil temperature and permafrost progression in the vegetation-protected zone, the team instrumented a rapidly degrading permafrost plateau in the western Kenai Peninsula lowlands of south-central Alaska. Researchers paired high-resolution soil temperature data with a suite of observed environmental variables across a topographically and vegetatively diverse area. This site is located at the warm southern fringe of the permafrost zone.

During the study, all locations but those with the highest relative-elevation and canopy density thawed rapidly. The stability of these topographically high locations was due to both vegetation and topographic protection. Low relative elevation locations thawed rapidly due to not having these protections, while moderate relative elevation locations, which shared many protections with high relative elevation locations, thawed rapidly due to their vulnerability to rain-induced warming and thaw. Additionally, the team observed an abrupt increase in average annual thaw rates during the duration of our study (2020-2022) compared to the time since the last study at the site (2015-2020). The study period contained the three snowiest years and three of the four wettest years since 2015. These snowy and wet years caused thaw-inducing environmental controls to be amplified, which caused a fourfold increase in thaw rates. As northern high latitudes continue to become warmer and wetter, and more of the permafrost zone experiences MAATs above 0°C, we may see similar environmental controls on permafrost progression across more of the permafrost region.