Transient Electromagnetic Surveys for the Determination of Talik Depth and Geometry Beneath Thermokarst Lakes

Abstract

Thermokarst lakes are prevalent in Arctic coastal lowland regions and sublake permafrost degradation and talik development contributes to greenhouse gas emissions by tapping the large permafrost carbon pool. Whereas lateral thermokarst lake expansion is readily apparent through remote sensing and shoreline measurements, sublake thawed sediment conditions and talik growth are difficult to measure. Here we combine transient electromagnetic surveys with thermal modeling, backed up by measured permafrost properties and radiocarbon ages, to reveal closed‐talik geometry associated with a thermokarst lake in continuous permafrost. To improve access to talik geometry data, we conducted surveys along three transient electromagnetic transects perpendicular to lakeshores with different decadal‐scale expansion rates of 0.16, 0.38, and 0.58 m/year. We modeled thermal development of the talik using boundary conditions based on field data from the lake, surrounding permafrost and a borehole, independent of the transient electromagnetics. A talik depth of 91 m was determined from analysis of the transient electromagnetic surveys. Using a lake initiation age of 1400 years before present and available subsurface properties the results from thermal modeling of the lake center arrived at a best estimate talk depth of 80 m, which is on the same order of magnitude as the results from the transient electromagnetic survey. Our approach has provided a noninvasive estimate of talik geometry suitable for comparable settings throughout circum‐Arctic coastal lowland regions.

Seasonal Subsurface Thaw Dynamics of an Aufeis Feature Inferred From Geophysical Methods

“…In a future study, a larger NMR loop size could improve the ability to discern the talik base, but it is important to keep in mind that the depth of investigation with large loops can be limited in very high latitudes by the high magnetic field inclination (Parsekian et al, ). It is possible that deeper imaging the talik base could also be accomplished using other deeper‐penetrating geophysical methods such as transient electromagnetics (Creighton et al, ) or airborne electromagnetics (Minsley et al, ), though we hypothesize that such surveys would have limited success at the Kuparuk site, where electrically resistive subsurface conditions observed during initial testing indicated that multifrequency EM surveys would likely yield little useful information. Direct current electrical resistivity methods (e.g., Minsley et al, ; Sjöberg et al, ; Yoshikawa & Hinzman, ) would be more suited to the resistive subsurface materials at the Kuparuk site and could potentially provide useful supporting information on talik thickness.…”

Thermokarst Lake to Lagoon Transitions in Eastern Siberia: Do Submerged Taliks Refreeze?

“…The modeled talik thickness after 5,000 years was 107 m, which is comparable to other studies. On the Alaskan coastal plain, thermokarst taliks over 90 m deep have been interpreted from TEM data (Creighton et al., 2018), and a talik 95 m deep was also interpreted from shallow seismics in the Lena Delta in Siberia (Schwamborn et al., 2002). In the initial phase of thermokarst development, the lake was completely isolated from Tiksi Bay (Figure 9a).…”

n-Alkane Characteristics of Thawed Permafrost Deposits Below a Thermokarst Lake on Bykovsky Peninsula, Northeastern Siberia

“…The total thaw depth (talik depth ∼32 m, altitude difference between lake and Yedoma uplands ∼20 m) of ∼52 m is relatively shallow for 8000 years of thermokarst development (M. Angelopoulos, personal communication, 2020). Previous talik modeling studies of Alaskan thermokarst lakes showed faster talik growth rates for lakes in North America (e.g., Ling and Zhang, 2003;West and Plug, 2008;Kessler et al, 2012;Creighton et al, 2018). However, talik growth could be slowed by characteristics of Siberian Yedoma, such as its higher ice volume in these sediments or the presence of bedfast ice during an extended shallow lake phase (<2 m).…”