Impact of permafrost thaw on hydrological connectivity between soils and surface waters

In recent decades, permafrost degradation and changing freeze-thaw conditions have intensified the hydrologic cycle and changed hydrogeological processes in Arctic environments. The gradual deepening of the active layer, the lowering of supra-permafrost water tables, the expansion of taliks, and in some places the thawing of ice-rich permafrost, restructure existing pathways and create new ones for water flow and infiltration. In particular, the abrupt thaw of ice-rich permafrost causes localised ground subsidence, which redirects water towards collapsed areas, resulting in the formation of thermokarst lakes. This study aims to explore the evolving connectivity between aquatic and terrestrial ecosystems in the context of permafrost thaw. With the deepening of the active layer, soil water is expected to infiltrate mineral-rich horizons. To detect these hydrological changes, geochemical tracers of mineral weathering such as silicon isotopes (δ30Si) and radiogenic strontium isotopes (87Sr/86Sr) are well-suited. We analyse these tracers in water samples collected during summer 2023 from lakes, ponds and soils in the areas of Beaver Creek, Yukon, Canada and of Churchill, Manitoba, Canada. In the Beaver Creek area, we compare a newly formed thermokarst lake to an older lake with long-standing soil-water connectivity but recent permafrost degradation nearby. In the Churchill area, geochemical tracers help determine whether and how permafrost thaw influences water chemistry in trough ponds and larger depressions formed by recent ice-wedge polygons degradation.