Introduction

Permafrost occupies about 80% of Siberia, the north-eastern part of Asia. Within its boundaries one can find large cities and industrial complexes. Permafrost stability is mainly governed by temperature. The changes in temperature (due to climatic variations or anthropogenic factors) may result in either permafrost degradation or stabilization. In this article we consider modern data collected on the temperature field of Siberian permafrost.

Temporal changes in the temperature of the upper rock layer are basically determined by air temperature variations (i.e. climate). Long lasting negative air temperatures on the Earth's surface result in ground cooling and the formation of frozen rock layers (permafrost). Terrestrial heat flow limits the depth extension of the permafrost .

Geocryological studies have shown that the permafrost in Siberia was mostly developed in Late Pleistocene, during the epoch of Sartanian glaciation (18-27 thousand years ago) (Kondratieva et al., 1993). The average air temperature at that time was about 8-10 °C less than at present. Under these favourable conditions permafrost spread over Siberia, with its southern border reaching 48-49° N. Subsequently the spatial extent of the permafrost was greatly reduced. In Western Siberia the southern permafrost border was displaced to the north up to 60°N. In Eastern Siberia the permafrost has almost the same spatial coverage but has likely been reduced in thickness. Heat transfer occurs extremely slowly in rocks, and thus a present temperature field of frozen rocks contains ("remembers") anomalies related to the most significant climate variations of the last epoch. As such permafrost is a huge natural "thermometer" sensitive to significant changes in climate.

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