Fluidogenic Landforms within the Area of Permafrost Occurence on the Shelf of the Pechora and Kara Seas

This research is based on the results of multibeam echo-sounding and high-frequency seismic profiling, carried out during the cruises of the R/V Akademik Nikolai Strakhov and Akademik Boris Petrov in 2018–2022. Regularities of changes of morphometric parameters and the internal structure of pingo-like features of the shelves of the Pechora and Kara seas were established. A morphometric analysis of pingo-like features was carried out, which made it possible to draw conclusions about their relative ages, as well as the degree of participation of the activity of near-bottom currents and slope processes in their modern dynamics. It was revealed that the density and morphological variety of pingo-like features depend on the geological and tectonic position of the bottom area, the presence and nature of permafrost, the intensity of degassing, and the timing of shelf flooding during the Holocene transgression. In areas of the shelf, where the depth exceeds 70–80 m, pingo-like features were formed at the early stages of the Holocene transgression; by now, the permafrost there has largely thawed. At the same time, pingo-like features retain their prominence in the relief and are actively transformed by the activity of bottom currents, slope and, possibly, pseudovolcanic processes associated with ongoing degassing. In shallow (up to 20–30 m) shelf areas close to the shore, pingo-like features are rare and, apparently, continue to form at the present time. At the same time, the large thickness and continuity of permafrost prevent active fluid flow, playing the role of a seal. Pingo-like features in the shallow-water are characterized by the morphology of cone-shaped mounds and the absence of signs of intensive degassing. At intermediate depths (from 20–30 to 70–80 m), in the presence of insular or discontinuous permafrost, under conditions of high fluid flow intensity in the area of fault zones and oil- and gas-bearing structures, the density of pingo-like features is maximal. In such areas, the localized processes of heaving and active degassing are combined in the near-surface sediments, this determines a wide variety of morphological types of pingo-like features.