Investigations of active soil layer on the Research station “Ice Base Cape Baranova’’ had been started in February 2016 after installation on the meteorological site sensors of Finnish Meteorological Institute: thermochain with IKES PT00 temperature sensors at depths of 20, 40, 60, 80 and 100 cm, soil heat flux sensor HFP, and two ThetaProbe type ML3 soil moisture sensors (Fig.1a). Based on the results of measurements annual cycle of soil temperature changes was revealed with amplitudes 10 – 15 ° C less than the amplitudes of surface air layer temperature (Ta) and especially the temperature of the soil upper surface (Ts), in great degree determined by short-wave radiation heating and long-wave radiation cooling. Approximation by linear fittings shows average rates of increase Ta – 0.4°C/year, Тs – 0.3°C/year, and temperatures of active soil layer – 0.2°C/year during period of observations.
Figure 1. Installation of FMI soil sensors (a) and soil active depth in 2016 – 2020 years (b).
The data on thermal regime of active soil layer and characteristics of energy exchange in atmospheric surface layer make it possible to draw the conclusion about the reason for abnormally warm state of the upper meter soil layer in summer 2020, despite in March during the whole period under study of active soil layer was the warmest in 2017. Comparison in temperatures of the underlying surface and characteristics of surface heat balance during period under study showed that in 2020 the temperature of the soil surface at the end of May for short time reached the temperature of snow melting. It is happened 25 days earlier than in 2017 and led to radical decrease in surface albedo, sharp increase of heat flux to the underlying surface, and increased duration of active soil layer heating and, as result, soil active layer depth (Fig1b). By the way January – September surface air temperature anomaly at station “Cape Tsheljuskin”, nearest to the Cape Baranov, was in 2020 on 4.4C higher of climatological average for 1932-2020.” Additionally, permafrost thawing studies using a manual contact method were carried out on polygon, organized in 2016 according CALM standards. These studies showed significant variety of soil active layer thicknesses in the relatively small area (~0.12 km2), which indicates spatial variability of microrelief, structure and thermophysical properties of soil, as well as vegetation, typical for Arctic desert. In spring 2021 five new thermo chains had been installed near research station “Ice base Cape Baranova” at depths 5 – 10 meters.