Lithological controls on seasonal freeze–thaw dynamics in coastal Antarctic permafrost: Insights from three years of continuous geophysical monitoring

Abstract. An automated electrical resistivity tomography (A-ERT) system was installed in the vicinity of the Czech Johann Gregor Mendel Station on James Ross Island, Antarctica, in March 2023. The 23 m long transect crosses a lithological boundary between fine-grained Cretaceous sedimentary rocks and coarser marine terrace deposits, with daily electrical resistivity measurements complemented by environmental observation data. The aim of this study was to characterize the freeze–thaw dynamics of the active layer and explore the relationship between thermal, hydrological, and geoelectrical parameters in a geologically complex coastal permafrost environment. Three years of continuous monitoring have demonstrated that the two lithological units are markedly distinct in their geoelectrical response, with the electrical resistivity values consistently higher within the marine terrace section. In both lithologies, close relationships between electrical resistivity and ground temperature, as well as with soil moisture, were identified. A slight freezing point depression was detected, at −0.1 °C within the marine terrace deposits and −0.3 °C within the Cretaceous sediments. Tracking the progression of the thaw front was possible within the Cretaceous sediments using the gradient method; however, this proved challenging within the marine terrace deposits due to a greater vertical heterogeneity. This research demonstrates the usefulness of A-ERT as a tool for active layer and permafrost monitoring in complex settings, where traditional point- or borehole-based methods may not adequately represent spatial variability.