Quantification of freeze–thaw hysteresis of unfrozen water content and electrical resistivity from time lapse measurements in the active layer and permafrost

Abstract

AbstractWe quantified seasonal, in‐situ variation in ground electrical resistivity, unfrozen water content, and ground temperature using daily and sub‐daily measurements in active layer and in permafrost on a high‐latitude monitoring site in West Greenland. The in‐situ unfrozen water content in a clayey soil undergoing phase change was 10% higher during freezing than during thawing at the same ground temperature, thus shifting the freezing curve parameterization seasonally. The freeze–thaw unfrozen water content hysteresis was a measurable part of the energy balance of the active layer and corresponds to 12.1% of the total yearly enthalpy change for our field site. We also observed and quantified hysteresis in the relationships between ground electrical resistivity and unfrozen water content, where the inverted resistivities during freezing in the temperature range from 0°C to approximately −4°C were up to one order of magnitude higher than during thawing at the same unfrozen water content. As a result, the petro‐physical models that uniquely derive soil unfrozen water content from bulk soil electrical resistivity measured from ground surface do not fully capture the complexity of the in‐situ processes. The hysteresis should therefore be considered in quantitative interpretation of ground resistivity changes in terms of ground temperature and ice content changes.