This study demonstrated the mechanical and electrical responses of Arctic saline permafrost during freeze-thaw processes, and suggested large uncertainty when estimating the unfrozen water content using electrical resistivity data.
Electrical and seismic signals during freeze thaw cycles of saline permafrost show characteristic changes with differential hysteresis behaviors. The uncertainty associated with unfrozen water content estimation based on electrical resistivity could be large.
Our study revealed low electrical resistivity and elastic moduli at temperatures down to approximately -10 °C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze-thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law.
Lawrence Berkeley National Lab
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. This research is supported through contract number DE-AC0205CH11231 to Lawrence Berkeley National Laboratory.
Wu, Y., S. Nakagawa, T.J. Kneafsey, B. Dafflon, and S. Hubbard. 2017. “Electrical and Seismic Response of Saline Permafrost During Freeze-Thaw Transition,” Journal of Applied Geophysics, 146,16-26. DOI: 10.1016/j.jappgeo.2017.08.008.
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