Magnetotelluric and Surface Nuclear Magnetic Resonance Measurements of Regional and Local Variability of Deep Saline Permafrost in Adventdalen, Svalbard

Abstract:

In most Arctic areas the interplay between permafrost and parameters such as climate variability and geological history is not well understood or documented. Nevertheless, knowledge on the thermal state of permafrost, its thickness and ice/water content is crucial for a credible assessment of the impacts of surface warming on a suite of environmental processes such as groundwater flow to riverbeds and the release of methane from areas of degrading permafrost. We carried out geophysical surveys using non-invasive Magnetotelluric (MT) and Surface Nuclear Magnetic Resonance (SNMR) techniques to map permafrost occurrence in Adventdalen, Svalbard, a river valley in a typical coastal Arctic landscape. MT, which is sensitive to changes in the electrical conductivity and can be used to distinguish saline, fresh, and frozen soils, was used to determine the total thickness of permafrost (potentially several 100s of meters). SNMR, which is directly sensitive the volume of liquid water, was used to determine the unfrozen water content and the heterogeneity of permafrost at depths of up to ~100 m. We collected measurements in transects across and along the valley which is filled with Holocene estuarine sediments. MT observations suggest that permafrost thickens substantially to up to several hundreds of meters along the ~12 km long transect from the coastal area inland. The electrical resistivities observed are relatively low (~200-400 Ωm) when compared to permafrost environments in Alpine settings, which is most likely attributed to a high salinity of pore waters in our study area. In the parts of the valley above the marine limit (~70 m above sea-level) SNMR did not detect any unfrozen water content. However, closely spaced SNMR transects across the valley several kilometers from the coast show a substantial signal, potentially due to unfrozen water content in supra-permafrost taliks near the main river channel. This is the first study to illustrate the ability of combining MT and SNMR data to map permafrost characteristics in saline environments. Combining these geophysical measurements with auxiliary data on the pore water salinities, temperature and the geological makeup of the study area will allow a thorough determination of ice-content and thermal state of deep permafrost in this coastal permafrost environment.