When Yedoma permafrost thaws: disturbances from lake drainage to thaw slump, and their impact on nitrogen cycling

The Arctic is warming four times faster than the global average, triggering the widespread degradation of permafrost and enhancing mobilization of vast, previously frozen soil nitrogen (N) and carbon (C) stocks. While C release associated with permafrost thaw is better documented, the liberation of permafrost N, a potential precursor to the strong greenhouse gas (GHG) nitrous oxide (N₂O), remains a critical knowledge gap. This is particularly relevant for ice-rich Yedoma deposits, which are highly vulnerable to abrupt thaw and the formation of disturbance features, such as retrogressive thaw slumps (RTSs), thermokarst lakes, and drained thermokarst lake basins (DTLBs). While RTSs are known hotspots for N₂O, recently formed DTLBs underlain by ice-rich Yedoma deposits with a high content of buried, poorly decomposed organic matter, remain largely understudied, although they are widespread across Yedoma landscapes. Importantly, there are no studies reporting N₂O fluxes from DTLBs, despite the high N mineralization expected after drainage, which might support high emissions.

Here, we report N₂O fluxes and N turnover processes from RTS and DLB on the Baldwin Peninsula, Western Alaska, underlain by ice-rich late Pleistocene Yedoma deposits. In situ fluxes were measured during the summer of 2024, alongside aerial surveys for high-resolution elevation and vegetation mapping with lidar and optical cameras. We conducted laboratory incubations for GHG production, including denitrification and ¹⁵N labeling to quantify gross rates of mineralization, nitrification, and dissimilatory nitrate reduction to ammonium (DNRA) using the ¹⁵N tracer method.

Our study reveals high N₂O emissions at both disturbance sites, demonstrating that DTLBs are emerging as significant sources of N₂O (up to 7.7 mg N m^-2 d^-1) emissions, comparable to known high emissions from thaw slumps. supported by high nitrate concentrations, reaching up to 205.1 µg N gDW^-1. We identified the role of environmental factors in driving the spatial variability in N₂O fluxes as well as N cycling. These findings suggest that as thermokarst lake drainage events increase across the Arctic, DTLBs in Yedoma uplands represent a major, expanding source of permafrost-driven N emissions that must be integrated into global climate feedback models. By tracking how N moves through the soil and how different environmental conditions, like moisture and thaw, trigger specific microbial processes, we can better understand the overall behavior of the N cycle and its growing role in these disturbance landforms.