Geophysical monitoring highlights the importance of hydro-thermal flow for talik formation

Measuring hydrological properties and processes in permafrost environments is known to be difficult, yet critical to develop cryohydrogeological models that can shed light on complex Arctic ecosystem processes. Geophysical techniques have been shown to be a valuable tool to assess the intermediate depths (1 - 10's of m) that are particularly important to understanding the impact of climate change on permafrost thaw dynamics. In this study we are aiming to answer two questions: (1) how variable are hydrological properties and processes in transitional permafrost environments, and (2) what is the impact of vegetation and snow-pack distribution on those properties? As part of the DOE NGEE-Arctic project, we present data from an electrical resistivity tomography monitoring transect located on the Seward peninsula that spans across different vegetation types, snowpack thicknesses and permafrost table depths. We focus on the subsurface response of disturbances due to snowmelt and extreme rainfall, and the long-term changes in resistivity. The results highlight considerable variability along the monitoring transect. Areas having tall shrub covered taliks have increased snow accumulation, which insulates the ground from cold air temperatures and allows for rapid ingress of snowmelt. Graminoid dominated areas have thinner snowpack, resulting in near-surface permafrost and surficial freezing, which lowers the hydraulic conductivity of the shallow subsurface and prevents snowmelt and rainfall from infiltrating into the subsurface. The results highlight the heterogeneity in thermal and hydrological fluxes in transitional landscapes, with increased fluxes in talik areas and presence of lateral flow between the domains that could be a driving factor in talik formation. Calibrated long-term resistivity changes indicate that permafrost temperatures increased by about 0.20°C over the two year monitoring period. Our results show that topography, vegetation and snow thickness are main drivers for talik development, and that hydrological properties change significantly with warming permafrost temperatures. These results will eventually help to improve predictions of Arctic feedback to climate changes.