Pingo-like features in the pechora sea: conditions, origin and stages of development

Using the results of multibeam echo sounding and seismic profiling performed during 2018—2019 on the R/V “Akademik Nikolay Strakhov” and all previously published data, a conceptual scheme of the pingo-like feature formation on the shelf of the Pechora Sea (south-eastern part of the Barents Sea between the islands of Kolguev and Vaygach) was developed. During interpreting the genesis of the bottom topography at a key-site with an area of about 12 km2, both new geophysical data obtained by the authors and previously published drilling materials were used. It has been established that formation of pingo-like features starts in the presence of submarine permafrost and subzero temperature of bottom waters under the influence of the fluid flow (degassing). Pingo-like feature development begins due to the formation of zones of abnormally high reservoir pressure below submarine permafrost as a result of vertical migration of fluids. The grouth of a pingo-like feature begins from the formation of a roll-like rise of the bottom due to the extrusion of frozen clayey strata to the near-surface part of the section. Subsequently, as a result of disruption of the continuity and partial thawing of permafrost, the growth of a pingo-like feature, which is essentially a mud volcanic structure, begins on the arch of the uplift. Fluid flow within a vertical channel up to the summit crater may be accompanied by freezing of the clayey strata as a result of the throttling effect. Mud flowing from the summit crater can freeze on the slopes of a pingo-like feature as a result of cooling of the fresh water contained in them under conditions of subzero bottom temperatures. A growth of the mud volcanic structure leads to a decrease in pressure near the base of submarine permafrost, that gradually thaws under the influence of fluid flow. This process leads to the gradual subsidence of roll-like rise and the appearance of compensation depressions. Based on the results of repeated monitoring of gas manifestations in water, it was established that more than half of the pingo-like features are currently active channels for the migration of fluids from the subsurface to the bottom surface and into the water column.