Soil Temperature Profiles of Two Alaskan Soils

Abstract

AbstractSoil temperatures of a thawed phase of a Pergelic Cryaquept were measured with copper‐constantin thermocouples at 20, 50, 100, 150, 210, 240, and 300 cm under a fallow plot for 5 yr in Fairbanks, AK. Soil temperatures of a Typic Cryorthent were measured the same way at 5, 10, 20, 50, 100, 150, and 300 cm under both grass and fallow plots for 22 yr in Palmer, AK. Fairbanks has a wider amplitude in annual air temperature variation and colder mean annual air temperature than Palmer. The mean annual soil temperature at 50 cm in Fairbanks is slightly lower (2.1°C) than in Palmer (3.0°C) under fallow plots. The difference between mean annual air temperature (MAAT) and mean annual soil temperature (MAST) is greater in Fairbanks (4.7°C) than in Palmer (1.7°C). The mean summer soil temperature is 9.5°C in Fairbanks and 13.1°C in Palmer, and the mean winter soil temperatures are −3.1 and −3.2°C, respectively. These data suggest that soil temperatures in both locations generally reflect the fluctuations in air temperature during summer and autumn. In winter, Fairbanks experiences colder air temperature than Palmer, yet mean winter soil temperatures are nearly the same. Evidently soils in Fairbanks are protected by snow cover against further cooling throughout the winter while soils in Palmer lack such protection due to the “glacier” wind and the freezethaw cycles that reduce the snow cover. The records showed that snow on the ground rather than total snowfall is accountable for the difference in temperature profiles between the soils. Both soils have forest as native vegetation. The removal of forest cover caused warming up of the soils based on elevated MAST on fallow plots. The classification of a Typic Cryorthent is not affected by such an increase in MAST. The MAST of a Pergelic Cryaquept rose above O°C, and thus changed from the pergelic to cryic temperature regime. The drainage of the Pergelic Cryaquept has also been improved, from poorly to moderately well‐drained. Perennial grass cover resulted in higher mean annual soil temperatures. The data suggest that the pergelic soil temperature regime needs to be redefined and also a new pergelic great group be established to facilitate soil surveys and interpretations in permafrost areas.