Post-glacial emergent permafrost processes in coastal and paleo-lagoon landscapes on Svalbard

Kurzfassung

Saline permafrost exists beneath shallow shelf seas, coastal plains shaped by past marine transgressions, and post-glacially uplifted landscapes that were once submerged. Salinity influences the freezing point and mechanical strength of permafrost and is therefore a critical parameter for assessing its stability. On Svalbard, the Kvadehuksletta region northwest of Ny-Ålesund features a diverse landscape comprising raised beach terraces, lagoons, paleo-lagoons (now lakes), and surface seeps. Our research aims to decipher how marine sediments transform after emergence. We hypothesize that ice formation during permafrost aggradation produces a porewater salinity gradient that triggers the downwards migration of salt in slowly uplifting sediments that are weakly susceptible to groundwater flushing. Sufficient salt build-up may lead to the formation of cryopegs – unfrozen layers or pockets within permafrost that persist at subzero temperatures to their elevated salt content. In summer 2024 and 2025, we carried out several electrical resistivity tomography (ERT) profiles, including three profiles (ranging from 800-2300 m in length) perpendicular to the coastline. The westernmost profile (collected in 2025) intersected a dynamic lagoon that was connected to the sea in 2024 but became completely cut off in 2025 by storm-surge deposits. To help delineate frozen and unfrozen permafrost conditions, electrical resistivity-temperature experiments on field samples collected from shallow cores (down to 250 cm) are currently underway. Laboratory tests indicate that the near-surface marine clays adjacent to the lagoon exhibit low resistivity values (< 10 Ωm) when thawed and freezing point temperatures down to -1.6 °C. The field samples are also being analysed for porewater chemistry (electrical conductivity, cations & anions, pH, stable water isotopes) and basic sedimentological properties like grain size. At two coring sites (1 paleo-lagoon, 1 beach setting), an annual ground temperature time series was also collected between field seasons. While the physical and electrical properties of the marine sediments are important to establish, so is their thickness. To determine depth to bedrock along selected ERT profile segments, we conducted multiple seismic refraction tomography (SRT) surveys (115 m length) in 2025 using a sledgehammer as an energy source. The synthesis of all datasets to describe uplifted permafrost is a work in progress, but preliminary conclusions suggest that cryopeg occurrence is most likely in low-lying coastal areas characterized by warm permafrost, occasional seawater submergence, and saline marine clays with low hydraulic conductivity.