Sensitivity of airborne geophysical data to sublacustrine and near-surface permafrost thaw

B J Minsley,M A Walvoord,T P Wellman,A Revil

doi:10.5194/tc-9-781-2015

Abstract

Abstract. A coupled hydrogeophysical forward and inverse modeling approach is developed to illustrate the ability of frequency-domain airborne electromagnetic (AEM) data to characterize subsurface physical properties associated with sublacustrine permafrost thaw during lake-talik formation. Numerical modeling scenarios are evaluated that consider non-isothermal hydrologic responses to variable forcing from different lake depths and for different hydrologic gradients. A novel physical property relationship connects the dynamic distribution of electrical resistivity to ice saturation and temperature outputs from the SUTRA groundwater simulator with freeze–thaw physics. The influence of lithology on electrical resistivity is controlled by a surface conduction term in the physical property relationship. Resistivity models, which reflect changes in subsurface conditions, are used as inputs to simulate AEM data in order to explore the sensitivity of geophysical observations to permafrost thaw. Simulations of sublacustrine talik formation over a 1000-year period are modeled after conditions found in the Yukon Flats, Alaska. Synthetic AEM data are analyzed with a Bayesian Markov chain Monte Carlo algorithm that quantifies geophysical parameter uncertainty and resolution. Major lithological and permafrost features are well resolved by AEM data in the examples considered. The subtle geometry of partial ice saturation beneath lakes during talik formation cannot be resolved using AEM data, but the gross characteristics of sub-lake resistivity models reflect bulk changes in ice content and can identify the presence of a talik. A final synthetic example compares AEM and ground-based electromagnetic responses for their ability to resolve shallow permafrost and thaw features in the upper 1–2 m below ground outside the lake margin.

Highlights

Permafrost thaw can have important consequences for the distribution of surface water (Roach et al, 2011; Rover et al, 2012), stream discharge and chemistry (O’Donnell et al, 2012; Petrone et al, 2007; Striegl et al, 2005; Walvoord and Striegl, 2007), and exchange between groundwater and surface water systems (Bense et al, 2009; Callegary et al, 2013; Walvoord et al, 2012)
For each of the 1000-year simulations, the static variables summarized in Table 1 are combined with the spatially and temporally variable state variables T and Si output by SUTRA to predict the distribution of bulk resistivity at each time step using Eqs. (1)–(6)
The influence of different lithologic units is clearly manifested in the predicted resistivity values, whereas lithology is not overly evident in the SUTRA state variables

Summary

Introduction

Permafrost thaw can have important consequences for the distribution of surface water (Roach et al, 2011; Rover et al, 2012), stream discharge and chemistry (O’Donnell et al, 2012; Petrone et al, 2007; Striegl et al, 2005; Walvoord and Striegl, 2007), and exchange between groundwater and surface water systems (Bense et al, 2009; Callegary et al, 2013; Walvoord et al, 2012). Climate feedbacks associated with permafrost thaw include changes in the amount of organic carbon stored in soils that is vulnerable to decomposition (Koven et al, 2011; O’Donnell et al, 2011) and subsequent methane and carbon dioxide released from soils by the degradation of organic material previously sequestered in frozen ground (Anthony et al, 2012). Minsley et al.: Geophysical signatures of sublacustrine permafrost thaw damage buildings, roadways, or pipelines due to ground settling, and thermal erosion that can alter coastlines and landscape stability (Larsen et al, 2008; Nelson et al, 2002)

Methods

Results

Discussion

Conclusion