GPR profiles and ground ice contents of permafrost cores in Cape Bounty, Melville Island, 2015

Investigations into the susceptibility of permafrost landscapes to thermokarst can be performed using various approaches, depending on the scale of investigation. In many cases, point-based field measurements are extrapolated to larger scales and vice versa. The integration of scales often requires some form of ground control in addition to remote sensing surveys, which are often exclusively conducted. As upscaling from discrete field measurements can provide spatial coverage and landscape-scale significance, downscaling from remote sensing can offer insight into processes and serve as calibration. Here we present a multiple-scale evaluation of a High Arctic field site, where differential interferometric synthetic aperture radar (DInSAR) showed subsidence between 2013 and 2015. Ground-based, cryostratigraphy measurements were combined with ground-penetrating radar (GPR) to investigate permafrost ice-content. The results indicate a connection between subsidence, as detected by DInSAR, and the locations where GPR surveys and permafrost coring indicated the presence of an ice-rich or massive ice layer near the base of the active layer. In addition, cryostratigraphic evidence of a thaw unconformity helped validate the geomorphological interpretation of the high-subsidence area as an old (before 1950) active layer detachment. The combination of methods indicated a localized landform-subsidence association, which brought further insight into the interpretation of DInSAR subsidence data. The framework presented in this study demonstrates the importance of site-specific investigations of thermokarst in order to understand the processes behind the remote sensing results.