The role of peat on permafrost thaw based on field observations

Rising temperatures result in permafrost degradation in cold regions, but with considerable spatial heterogeneity due to local factors including peat. Peat plays an important role in the permafrost carbon cycle by impacting the soil thermal and hydrologic characteristics. Here we use field observations to describe the role of peat on permafrost thaw based on comparisons at two sites: EBoTA characterized by primarily peat, and PT5 with more mineral soils. Compared to PT5, soil temperature at the EBoTA site was lower in the warm season, but higher in the cold season. Freezing onset was generally 0-19 days later at the PT5 site compared to EBoTA throughout the soil column, except at the 0.1 m depth where it occurred 11 days earlier. The average thawing onset at PT5 was 18-96 days earlier. There were 20-119 more freezing days and 19-118 fewer thawing days at EBoTA than at PT5, and the zero annual amplitude and active layer thickness were lower at EBoTA. Finally, the mean annual ground temperature was greater at PT5, and was even above 0 degrees C in three recent years. These results illustrate peat's thermal insulation effect on permafrost due to its low thermal conductivity and high moisture content. Snow depth increases also amplify the insulation effect. These field observations therefore not only verify, but also quantify the protective role of peatlands on permafrost.