Time-Domain Electromagnetics for Subsea Permafrost Mapping in the Arctic: The Synthetic Response Analyses and Uncertainty Estimates from Numerical Modelling Data

Abstract

Subsea permafrost stability is the key to whether pre-performed methane sequestered in hydrate deposits escapes to the overlying strata. By making use of the 1D numerical modeling and field data, we analyze the capabilities of the time-domain (transient) electromagnetic method (TDEM) when being applied for subsea permafrost mapping, and study the effect of the background resistivity structure on the inversion models’ accuracy for a series of settings typical for the East Siberian Arctic Shelf—the broadest and shallowest shelf in the world ocean, which represents more than 70% of the subsea permafrost. The synthetic response analysis included the construction of a series of resistivity models corresponding to different settings (presence/absence of ice-bonded permafrost layer, different position of its top and bottom boundaries, different width and thickness of thawed bodies or taliks, variable seawater depth and its resistivity), and calculation of synthetic apparent resistivity responses used to assess their sensitivity to changes in the target parameters of the resistivity structure. This was followed by regularized inversion of synthetic responses and comparing resulting models with original (true) ones, which allowed us to understand the possible uncertainties in the geometry and resistivity of the reconstructed permafrost layer, depending on seawater depth and unfrozen layer thickness, as well as confirm the overall efficacy of TDEM technology for the subsea permafrost imaging. That is crucially important for understanding the current state of the subsea permafrost-hydrate system and possible future dynamics.

Satellite-Based Evaluation of Submarine Permafrost Erosion at Shallow Offshore Areas in the Laptev Sea

“…However, at certain shelf areas, the submarine permafrost is discontinuous and contains gas and gas hydrate accumulations. The submarine permafrost layer has a thickness of several hundred meters, which degrades at a rate of about 14-18 cm per year [7,11,46,47]. 023, 15, x FOR PEER REVIEW 3 of 18 the western and eastern regions of the Eurasian Arctic influenced by cyclonic activity of the Atlantic and Pacific oceans, respectively, the Laptev Sea has severe climate conditions including extremely low winter temperatures and a short ice-free season [43].…”

“…However, at certain shelf areas, the submarine permafrost is discontinuous and contains gas and gas hydrate accumulations. The submarine permafrost layer has a thickness of several hundred meters, which degrades at a rate of about 14-18 cm per year [7,11,46,47]. The most intense seafloor erosion occurs in the largest offshore shallow area of the Laptev Sea westward from the Stolbovoy Island, which consists of the closely located Vasilyevskaya and Semenovskaya shoals (hereafter referred to as VS) [41] (Figure 1b).…”