Geophysical Monitoring Shows that Spatial Heterogeneity in Thermohydrological Dynamics Reshapes a Transitional Permafrost System

Abstract

The average temperature of permafrost has increased globally by about 0.4°C in the last century. This is partly due to the Arctic amplification of an increase in air temperature in the Northern Hemisphere, but also due to increased snow thickness, especially in areas of discontinuous permafrost (Biskaborn et al., 2019). This change in temperature changes the physical properties of the subsurface, with impacts on infrastructure (Hjort et al., 2018), groundwater resources, vegetation distribution (Jorgenson et al., 2013; Lloyd et al., 2003), carbon and nitrogen cycling (Petrone et al., 2006), and greenhouse gas emissions (Jansson & Taş, 2014), leading to further acceleration of climate change. Jorgenson et al. (2010) show that complex feedbacks exist between permafrost dynamics and topography, vegetation distribution, snow pack, ground temperature, and subsurface hydrological properties. Rising permafrost temperatures cause increasing hydraulic conductivities in the soil to bedrock column, enabling or enhancing surface water-groundwater interactions, changes to the groundwater residence times, and eventual alterations to groundwater and stream water temperature and compositional dynamics (Hinzman et al., 2005; Ireson et al., 2013). These changes in hydrology enhance the importance of the deeper subsurface for carbon and nutrient cycling (Koch et al., 2013; Lyon et al., 2010), and are particularly important for discontinuous permafrost, which accounts for 19% of the Northern Hemisphere's land surface that is covered by permafrost, that is 4.4 × 10 6 km 2 (Zhang et al., 2003). This region is characterized by a Abstract Climate change is causing rapid changes of Arctic ecosystems. Yet, data needed to unravel complex subsurface processes are very rare. Using geophysical and in situ sensing, this study closes an observational gap associated with thermohydrological dynamics in discontinuous permafrost systems. It highlights the impact of vegetation and snow thickness distribution on subsurface thermohydrological properties and processes. Large snow accumulation near tall shrubs insulates the ground and allows for rapid and downward heat flow. Thinner snow pack above graminoid results in surficial freezing and prevents water from infiltrating into the subsurface. Analyzing short-term disturbances, we found that lateral flow could be a driving factor in talik formation. Interannual measurements show that deep permafrost temperatures increased by about 0.2°C over 2 years. The results, which suggest that snowvegetation-subsurface processes are tightly coupled, will be useful for improving predictions of Arctic feedback to climate change, including how subsurface thermohydrology influences CO 2 and CH 4 fluxes. Plain Language Summary When permafrost thaws, water can flow quicker through the ground, creating a very complex subsurface flow system. In this study, we gain detailed insight into these complex processes by measuring the electrical resistivity of the ground daily. Our results show that the type of vegetation and the ...

A Review on Applications of Time-Lapse Electrical Resistivity Tomography Over the Last 30 Years : Perspectives for Mining Waste Monitoring

“… 2002 ; Uhlemann et al. 2021 ). Moreover, this type of autonomous monitoring system allows for near real-time data transfer, processing and can send alerts (Web, email or SMS) if predefined thresholds of moisture content (or other parameters) are exceeded, which could be highly valuable to detect any deterioration of the geochemical or geotechnical stability of mining wastes.…”

An overview of multimethod imaging approaches in environmental geophysics

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Rapid and Gradual Permafrost Thaw: A Tale of Two Sites

“…Electrical resistivity tomography (ERT) measurements have proven useful in characterizing permafrost distributions (Briggs et al., 2014; Douglas et al., 2016; Lewkowicz et al., 2011), particularly when combined with downhole nuclear magnetic resonance (NMR) measurements that estimate in situ volumetric water content with depth (James et al., 2021; Kass et al., 2017; Minsley et al., 2016). Furthermore, repeat ERT measurements can detect changes in subsurface unfrozen water over time (Uhlemann et al., 2021). Warming temperatures and changes in the type, amount, and timing of precipitation observed here (Figures 1b and 1c) and elsewhere across northern latitudes are causing spatially and temporally variable thaw trajectories (Douglas et al., 2020; Farquharson et al., 2022).…”