Abstract
Lakes in Arctic systems contribute to hydrologic storage, biogeochemical cycling, and permafrost thaw. Here, we have used surface nuclear magnetic resonance (NMR) measurements on lakes of Alaska’s North Slope to investigate the extent of permafrost thaw below lakes with different annual ice conditions. Our purpose is to understand if annual lake ice conditions are related to development of thawed permafrost below lakes. We investigated 10 lakes and two terrestrial permafrost control sites using surface NMR and direct measurement under spring conditions when lake ice is nearly at its thickest. We did not observe unfrozen water below our surveyed bedfast ice lakes, whereas unfrozen water (indicating permafrost thaw) was measured below floating ice lakes. We found that transitional ice lakes, ones that alternate between floating and bedfast ice conditions over multiyear timescales depending on winter ice growth and lake level conditions, have complex vertical unfrozen water content profiles attributed to sporadic periods of thaw. Based on that finding, we speculate that predicting the presence of talik based on remotely sensed lake ice conditions is unreliable. We applied a scheme to subtract the lake water signal from the NMR data and found the resulting inversions to be improved.
Highlights
The Arctic climate is changing with implications for weather, ecosystems, biogeochemical cycles, and human habitability
The slightly higher noise observed in the Peatball Bluff (PBB) data set (Figure 4a2) compared with the INI and TES data sets (Figure 4a1, 4a3, and 4a4) can be attributed to the larger loop used in the measurement at PBB
5.4 m at ITIL16, the water content is generally
Summary
The Arctic climate is changing with implications for weather, ecosystems, biogeochemical cycles, and human habitability. Transitional lakes are expected to have talik development related to the direction of ice regime change, potentially even including layers of variably frozen and thawed material related to periods of either floating or bedfast ice conditions. All of these assumptions may be readily modeled; they are difficult to measure for two main reasons. Airborne electromagnetic imaging has been successful at observing taliks, related to discontinuous permafrost (Minsley et al, 2012); it is ambiguous to interpret resistivity values as either contrasts in the substrate or freeze/thaw state Other methods such as ground-penetrating radar have proven valuable for very shallow investigations related to lake ice and lake sediments (Shwamborn et al, 2002; Jones et al, 2013), but they do not have the depth sensitivity to fully explore the talik geometry and physical properties. Please refer to Weichman et al (2002), Walsh (2008), and Behroozmand et al (2015) for additional details and comprehensive reviews of the surface NMR principles
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