Drivers and consequences of changing groundwater dynamics in Arctic coastal systems

Arctic hydrosystems are undergoing rapid change, driven by warming temperatures, shifting precipitation regimes, and increasing climate extremes. In Arctic coastal settings, these terrestrial and atmospheric pressures are compounded by ocean-driven change, including storm-surge inundation and saltwater intrusion that can introduce heat and solutes to tundra soils and near-surface aquifers. Despite the strong groundwater-surface water connectivity and pronounced seasonality that characterize cold-climate hydrosystems, we still lack a process-based understanding of how ocean variability interacts with coastal groundwater dynamics and the resulting ecohydrological and biogeochemical feedbacks.

Here we synthesize recent work from the Arctic Coastal Plain of Alaska that quantifies two-way interactions between ocean conditions (event to seasonal scales) and groundwater response, and links these dynamics to hydro-thermal and biogeochemical change. We combine year-round time series of groundwater and surface-water levels with multi-depth soil temperature profiles, electromagnetic surveys of subsurface electrical conductivity, and seasonal measurements of porewater chemistry and thaw depth across tundra environments spanning gradients in inundation frequency. Across sites, elevated porewater salinity and higher subsurface electrical conductivity were associated with vegetation degradation and thicker active layers. A year-long record of soil temperature profiles shows that inundation-driven shifts in vegetation and soil properties alter surface energy balance and increase soil thermal conductivity, yielding summer soil temperatures up to 10°C warmer than at undisturbed sites. These warming patterns cannot be explained by freezing-point depression alone, highlighting the importance of coupled ecological-hydrogeological-thermal feedbacks.

We further show that spatial variability in active layer thickness modifies surface-subsurface connectivity and water exchange, with implications for both saltwater intrusion pathways and the magnitude of coastal groundwater discharge. Our results demonstrate that coastal Arctic groundwater vulnerability emerges from interacting processes across hydrologic, thermal, and ecological domains, and that integrating geophysics, year-round monitoring, and porewater biogeochemistry is essential for anticipating how permafrost-bound coastlines will respond to continued warming and ocean change.