Investigating Permafrost Aggradation below a Cascading Arctic Lake Drainage using Transient Electromagnetics and Thermal Modeling

            The Arctic is warming at four times the rate of the global average which threatens the existence of permafrost. Independent of anthropogenic climate change, both degradation and aggradation of permafrost in the Arctic frequently occurs below lake and drained lake basin (L-DLB) systems. If global climate change continues at the current rate, we expect that permafrost degradation would accelerate during the extant lake phase, and that permafrost aggradation would slow and even cease if mean air temperatures begin to approach or exceed 0⁰C. Also, L-DLB systems are ubiquitous in Arctic permafrost regions, occupying between 20 - 33% of the total land of the northern circumpolar permafrost region with some areas, like the Arctic Coastal Plain of Alaska (ACPA), exceeding 80% coverage. Therefore, it is vital to study L-DLB systems to understand the dynamics of permafrost regimes in the context of a warming climate. Currently, there are limited studies that have measured permafrost dynamics below L-DLBs, almost no studies have measured aggradation immediately after lake drainage, and to our knowledge there are no designated sites to monitor aggradation rates under naturally occurring DLBs. In 2020, we were informed by local and traditional knowledge experts from Utqiagvik that a lake drainage event was likely to occur at the Bugeye Lakes Complex in the ACPA. Over the next two years, we closely observed a cascade lake drainage event that partially or completely drained all four Bugeye Lakes. This was the first time a naturally occurring cascade drainage event has been captured in real time which has provided a unique opportunity to establish a monitoring site for permafrost aggradation. To estimate talik thicknesses and aggradation rates after lake drainage, we have acquired transient electromagnetic (TEM) measurements at Bugeye Lakes in April 2022 and will repeat TEM measurements in April 2026. We have also used transient thermal models to compare with our geophysical observations. Additionally, we expect that our work will provide a framework for establishing a L-DLB monitoring site at the Bugeye Lakes Complex, which would be critical to improve our understanding of permafrost dynamics under a warmer climate regime.