Soil-cryogenic complexes of west Siberian tundra

Soil-cryogenic complexes (the system of «permafrost-affected soils – upper permafrost»), located at the interaction hotspot of the biosphere and the cryosphere, were studied at five key sites in Northwestern Siberia situated on geomorphological terraces of different origin – from marine to fluvial and lacustrine – and age (Late Pleistocene and Holocene). In the context of the present-day permafrost zone transformation under global climate change and local anthropogenic impact, they are of considerable ecosystem significance. Based on the geomorphological and cryolithological studies, it was concluded that fully developed soil-cryogenic complexes (SCCs), comprising the active layer (AL), transient layer (TL), and intermediate layer (IL), are spatially limited in the study area due to lithogenic and ecosystem factors. Due to the wide distribution of deeply thawing sandy, ice-poor sediments where continuous and thick vegetation cover is unable to develop, morphologically expressed TL was absent, having already fully thawed. Modern soil formation most often occurs directly above the degrading IL or even Late Pleistocene frozen sediments containing fragments of ground ice. Relatively stable permafrost conditions and full-profile SCCs were observed in the thick peat massifs only where the presence of thick organic horizons reduces the heat flux and limits the active layer thickness (ALT). Furthermore, a number of hazardous geomorphological cryogenic processes – including thaw ground subsidence, thermal denudation, and thermal abrasion in coastal areas – contribute to the degradation of SCCs, thereby diminishing their protective role in permafrost preservation. A comprehensive approach to the assessment and forecasting of the ecological state and dynamics of fragile Arctic ecosystems, based on SCC research, could provide a deeper understanding of both natural and anthropogenic processes.