Imaging Spatial and Temporal Subsurface Variability in a Discontinuous Permafrost Environment

Predicting the feedback of Arctic environments to warming temperatures remains a challenge. Quantifying and monitoring soil and permafrost thermo-hydrology can improve our understanding of the hydro-biogeochemical processes and can substantially advance modelling of Arctic ecosystems. Particularly in discontinuous permafrost, with a co-existence of active layer, talik, and permafrost, thermal and hydrological properties are highly variable, both spatially and temporarily. Imaging the subsurface dynamics of such system will not only provide a better understanding of its feedback to warming temperatures and the related changes in subsurface storage and flux of water, carbon, and nutrients, but will also enable a predictive understanding of Arctic environments that are yet to undergo a transition from frozen to unfrozen conditions.

We focus on the geophysical imaging of permafrost distribution and dynamics within a watershed on the Seward Peninsula, Alaska, which acts as a study site for the Next-Generation Ecosystem Experiments (NGEE). We acquired seismic and geoelectrical data across the watershed. The results highlight the co-existence of shallow and deep permafrost, and taliks, and their potential link to the subsurface geology. By jointly inverting those data sets we estimate the subsurface ice/water/rock fraction, which allows for approximating the base of permafrost. Spatially extensive low-induction electromagnetic data show a good correlation with snow thickness, highlighting the insulating properties of the snow pack.

Additionally, geoelectrical, and distributed temperature and moisture data were acquired along a transect for two consecutive years. The data show spatial and temporal variability linked to the vegetation distribution, with rapid responses related to snowmelt and intense rainfall events, and generally decreasing resistivities and increasing temperatures over the monitoring period. Finally, by linking laboratory analysis of soil cores to the field data, we can transform geophysical parameters into thermo-hydraulic quantities, which are suited for integration into ecosystem models.