Home – Home – Jornals – Earth’s Cryosphere 2023 number 5

We performed geophysical studies to determine the structure of the frozen layer around and below the Uomullyakh-Kyuel Lagoon, the lagoon itself being a reference landform sculpted by thermokarst and thermal abrasion of the sea shoreline. The main purpose of the study was to determine talik depth under lagoon or the position of the subaquatic permafrost boundary. We performed electromagnetic and electrical studies with transient electromagnetic sounding and electrical resistivity tomography from lagoon ice during winter period and from water surface in summer. We matched borehole section data with temperature data from this same borehole and also with surface geophysical data. This comparison showed patterns of modern and relict taliks in the form of low electrical resistivity layers. We demonstrate that modern talik has developed to the depth of 30 m. At the same time, the relict talik is located between depths of 80-100 m, which correlates with data acquired by other researchers. We suggest that relict talik has a hydrological connection to the strata located under the seafloor; therefore it is seen clearly on geoelectric cross section. The lake that formed the relict talik had a size of at least 1450 by 900 m. Electrical resistivity tomography data acquired from the lagoon surface shows fragments of boundaries between frozen and unfrozen permafrost. Numerical modeling shows that electrical resistivity tomography quantitatively underestimates resistivity of the frozen permafrost by 5 to 10 times. In the subaerial-subaquatic transition zone, we track a gradual descent of the permafrost upper boundary and map a permafrost overhang, which sometimes appears beneath shallow water bodies. We suggest that gradual decrease of electrical resistivity in the direction from the seashore to the sea basin corresponds to the amount of salt transported into sediments and increase in their temperature.