Thermal Regime of Permafrost in the Borehole Depending on the Snow Cover Thickness in the Area of the Polar Station “Samoilovsky Island” (Lena River Delta)

Abstract

The paper analyzes long-term temperature monitoring data in a borehole at the station “Samoylov Island” in the Lena River delta. Temperature measurements over 12 years (from late 2006 to early 2019) show a warming of permafrost at a depth of 26.5 m by 1.3 °C. At the same time, air temperature does not show a noticeable rise during this period. To identify the factors influencing the temperature in the borehole, a numerical simulation of the soil temperature changes was carried out. The simulation was performed taking into account the warming effect of snow cover on the the freezing/thawing processes of the upper active layer. Based on the modeling results, it was concluded that the warming of the borehole is associated with increasing in the thickness of the snow cover due to the construction of buildings that accumulate snow around the borehole area. The thermal diffusivity of soils near the borehole at different depths (from 10 down to 21 meters) is amounted within a range of (0.88–1.18)⋅10–6 m²/s that was determined using the 12-year temperature records (from 2006 to 2019) of seasonal temperature f luctuations at different depths. The time necessary for the borehole to reach a new thermal regime under conditions of an increasing snow thickness accumulating near the borehole was estimated. A new steady-state regime of the borehole was determined, in which the average temperature values at depths of 15.75, 20.75 and 26.75 meters may reach by 2062 are as –4.8, –5.1, –5.5 °C, respectively; in 2018, these temperatures were equal to: –6.81, –7.42, –7.86 °C.