Ice content estimation in a Palsa at Aidejavri (Norway) using High-Frequency Induced Polarization (HFIP)

Permafrost is an import carbon sink on earth and its thawing due to global warming is considered one of the most critical tipping points in climate change. Among permafrost landforms, palsas – frost-heaved mounds with ice-rich cores - are particularly sensitive to global warming. Palsas form under conditions of alternating freezing and thawing, leading to the accumulation of ice lenses that elevate the ground surface. As global temperatures rise, palsas are increasingly subject to degradation, which results in subsidence and the release of stored greenhouse gases, profoundly affecting local and global ecosystems.

This study focuses on a palsa located in a peat mire at Aidejavri/Norway, aiming to characterise it using geophysical methods. High-Frequency Induced Polarization (HFIP) was employed to quantify ice content across the palsa. HFIP is an innovative method that measures the frequency-dependent electrical conductivity in the frequency-range between 100 Hz and 100 kHz. In that range, the electrical permittivity of water ice exhibits a sharp decrease, making HFIP suitable for ice-content estimation. The HFIP data were inverted in 1D to isolate the polarization response of the subsurface from induction. A two-component dielectric mixture model was used to invert the data in 2D, providing detailed spatial insights into ice distribution. The results indicate high ice contents underneath the palsa, togehter with clear signs of degradation by decreasing ice contents at the edges where ponds are visible at the surface.

To supplement these findings, electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) were applied. ERT revealed the lateral extent and resistivity contrasts of the permafrost, while GPR delineated the upper boundary of the frozen layer. Together, these methods provided a comprehensive view of the palsa’s internal structure.

This study shows that HFIP, paired with effective pre-processing and additional methods, serves as a dependable approach for examining ice-rich permafrost. The results can be used to characterize the current state of the palsa and provide data on ice content and spatial variability. The data constitute the beginning of repetitive measurements, that aim to capture temporal changes in the palsa’s internal structure and ice content. These repeated observations will help track the dynamics of permafrost degradation over time, offering insights into how rapidly such landforms respond to climatic variations.