The accumulation of polycyclic aromatic hydrocarbons (PAHs) in the profiles of permafrost-affected peat mounds is related to certain groups of plant residues produced in the Atlantic climatic optimum of the Holocene. Both heavy (benzo[ghi]perylene, dibenz[a,h]anthracene, and benzo[b]fluoranthene) and light (pyrene and naphthalene) PAHs predominate in them. The polyarenes preserved in the permafrost horizons are not subjected to transformation in contrast to the polyarenes in the active layer. Dynamic freeze-thaw processes at the boundary between seasonally thawed and permanently frozen layers result in considerable transformation of plant remains, humic substances, and nonspecific organic compounds with the accumulation of 5-6-nuclear PAH structures. The composition of PAHs in peatlands and a significant increase in the weight fraction of PAHs at the boundary between seasonally thawed and permafrost layers may serve as indicators of permafrost response to climate changes in high latitudes.

Soil temperature regimes were studied in three ecosystems of the north of Western Siberia in the zone of isolated permafrost: the forest ecosystem with gleyic loamy sandy podzol (Stagnic Albic Podzol), the flat-topped peat mound ecosystem with humus-impregnated loamy sandy to light loamy peat cryozem (Histic Oxyaquic Turbic Cryosol (Arenic)), and the peat mound (palsa) ecosystem with oligotrophic destructive permafrost-affected peat soil (Cryic Histosol). Annual temperature measurements in the soil profiles demonstrated that these soils function under different temperature regimes: very cold permafrost regime and cold nonpermafrost regime. The following annual temperature characteristics proved to be informative for the studied soils: sums of above-zero temperatures at the depths of 10 and 20 cm, the maximum depth of penetration of temperatures above 10A degrees C, and the number of days with daily soil temperatures above (or below) 0A degrees C at the depth of 20 cm. On the studied territory, the insulating effect of the snow cover in winter was at least two times more pronounced than the insulating effect of the vegetation cover in summer. Cryogenic soils of the studied region are characterized by the high buffering towards changing climatic parameters. This is explained by the presence of the litter and peat horizons with a very low thermal diffusivity and by the presence of permafrost at a relatively shallow depth with temperature gradients preventing penetration of heat to the permafrost table.