Saturation Patterns of Water Track-thermoerosional Gully Complexes Situated on Hillslopes Underlain by Continuous Permafrost

Arctic air temperatures are rising at triple the global rate causing permafrost to thaw, potentially releasing massive amounts of carbon dioxide and methane into the atmosphere. Because Arctic soils release three times more carbon when unsaturated versus saturated, it is critical to understand how changes in climate will alter spatiotemporal patterns of soil saturation. To quantify these patterns, we are investigating features called water track-thermoerosional gully complexes (TGC). Within a single catchment, TGCs oscillate between stable water tracks - shallow curvilinear depressions - and thermoerosional gullies - incised gullies that form when ice wedges thaw. We hypothesize that water tracks and thermoerosional gullies within TGCs exhibit distinct saturation patterns due to unique topographic and hydraulic characteristics. To test this hypothesis, we are studying three TGCs located on hillslopes in northern Alaska that are underlain by continuous permafrost. Each TGC is instrumented with shallow groundwater wells, soil moisture sensors, soil temperature sensors, precipitation gages, and water presence-absence sensors that have been collecting data continuously since June 2022. Additionally, we are manually measuring active layer depth and near-surface soil moisture within or adjacent to the features. Preliminary findings from manual measurements show that near-surface soil moisture patterns are more heterogeneous within the features than the adjacent hillslopes. Additionally, we found soil moisture at the edge of the TGCs was more responsive to rain compared to the adjacent non-TGC hillslopes. Furthermore, continuous presence-absence data within the features indicate that saturation patterns were consistent across all three TGCs, with the uppermost portions of the stream network drying first. Finally, initial groundwater, soil temperature, and active layer thickness data suggest that early thaw-season groundwater flow persists through the organic layer at all three TGCs. Future work will aim to integrate this field data with remote sensing analysis to better understand soil saturation patterns across the upland Arctic, which in turn will help us discern how carbon emissions will change in a warming climate.