Abstract
This paper provides information on active layer thickness (ALT) dynamics, or seasonal thawing above permafrost, from a Circumpolar Active Layer Monitoring (CALM) site near the city of Norilsk on the Taimyr Peninsula (north-central Siberia) and the influences of meteorological and landscape properties on these dynamics under a warming climate, from 2005 to 2020. The average ALT in loamy soils at this 1 ha CALM site over the past 16 years was 96 cm, higher than previous studies from 1980s conducted at the same location, which estimated ALT to be 80 cm. Increasing mean annual air temperatures in Norilsk correspond with the average ALT increasing trend of 1 cm/year for the observation period. Active layer development depends on summer thermal and precipitation regimes, time of snowmelt, micro-landscape conditions, the cryogenic structure (ice content) of soils, soil water content leading up to the freezing period, drainage, and other factors. Differences in ALT, within various micro landscape conditions can reach 200% in each of the observation periods.
Highlights
The active layer is a soil or rock layer between the ground surface and permafrost that thaws in the summer season and freezes again in the winter (General Permafrost Science 1978)
In later work it was noted that the smallest depths of seasonal thawing in the Norilsk region were typical for floodplains and terraces covered with peat, and are 0.3 to 0.8 m; maximum thickness was from 4.5 to 5.5 m on gently sloping areas of the plateau, which is composed of highly fractured, highly conductive basalts covered by thin Quaternary sediments (Demidyuk 1989)
A decrease in the severity of the climatic conditions in Taimyr has contributed to major changes in the natural and anthropogenic systems (Kirdyanov et al 2012; Nyland et al 2017; Grebenets et al 2016)
Summary
The active layer is a soil or rock layer between the ground surface and permafrost that thaws in the summer season and freezes again in the winter (General Permafrost Science 1978). Specialists from the Committee for the Study of Permafrost of the Academy of Sciences of the USSR arrived in Norilsk in 1936 under the leadership of V.F. Tumel, who organized a special group under the management of NorilskStroy. A laboratory for the study of physical and mechanical properties of soils and a permafrost station under the leadership of engineer M.V. Kim were organized. In later work it was noted that the smallest depths of seasonal thawing in the Norilsk region were typical for floodplains and terraces covered with peat, and are 0.3 to 0.8 m; maximum thickness was from 4.5 to 5.5 m on gently sloping areas of the plateau, which is composed of highly fractured, highly conductive basalts covered by thin (up to 0.5 m) Quaternary sediments (Demidyuk 1989). Thaw depth data were obtained during thermal measurements in boreholes by interpolation to determine the depth of the 0°C isotherm
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