Geophysical Investigations of Drained Lake Basin Taliks, North Slope, Alaska

Abstract:

Combined, lakes and drained lake basins (DLBs) occupy up to 80% of the Arctic lowlands in Alaska, Canada, and Russia. Developed in permafrost terrain, deeper lakes tend to have a thawed zone, or talik, of unfrozen sediments below the lake bed. Processes occurring after lake drainage include permafrost aggradation as talik refreezes and vegetation succession, both of which have implications for hydrology, the carbon cycle, and landscape evolution. Depending on the talik thickness, lithology, climate, and surrounding permafrost conditions, remnant taliks are estimated to refreeze over several decades associated with top-down and bottom-up permafrost aggradation. However, considering the scarcity of direct measurements of DLBs talik geometry and the wide range of DLB ages, sizes, and locations, we are motivated to gain a better understanding of where taliks exist below DLBs and the rates of talik refreezing. Here, we used transient electromagnetic (TEM) and surface nuclear magnetic resonance (NMR) soundings in conjunction with talik refreeze modeling to study permafrost aggradation below DLBs on the North Slope of Alaska. We conducted geophysical measurements on eight DLBs and two lake-free control sites, which are primary surfaces assumed to have not experienced lake formation and drainage recently. Moreover, borehole logs provided lithologic description, resistivity, and temperature profiles to help our interpretations. Historical aerial imagery provided the approximate time of lake drainage. Our results reveal the presence of remnant taliks below various DLBs that drained after 1949 (oldest imagery), whereas in DLBs that drained before 1949 the taliks seem partially or completely refrozen. Thermal modeling results are consistent with the geophysical results, providing two lines of evidence of the presence of remnant taliks. Complete lake drainage results in faster permafrost aggradation rates than a partial drainage due to the thermal properties of remnant lake water. Modeling indicates that warmer and wetter conditions in the future will slow permafrost aggradation and lake drainage events will probably increase. Our findings provide valuable information to predict future permafrost aggradation rates below DLBs and their impacts on the water and carbon cycles in the Arctic.