Aufeis Formation and Climate Change

In river channels in artic environments, groundwater that discharges to the land surface during winter can freeze in the channel, forming large sheet-like masses of layered ice called aufeis. Water stored in aufeis is released slowly as the aufeis melt during summer, providing a critical course of water to the Arctic river ecosystems late into the summer when other water resources are reduced. Under warming conditions in the Arctic, the quantity of water stored in aufeis may be reduced and the release of water by melting of the aufeis may end earlier in the summer. The processes that lead to the formation of aufeis are not well understood; however, an understanding of these processes is necessary to predict how rising air temperature may affect aufeis formation and the availability of water in Arctic river ecosystems. This work uses numerical simulation to evaluate a conceptual model of subsurface hydrogeothermal conditions that can lead to the formation of aufeis in the Kuparuk aufeis field on the North Slope of Alaska. At this site, groundwater flows year-round through a talik above the permafrost and beneath the seasonally-frozen active layer just beneath the land surface. Groundwater in this talik discharges to the land surface through unfrozen gaps in the active layer, where it can freeze and form aufeis. We developed a 2-D heterogeneous vertical profile model to show that subsurface water can discharge to the land surface through subvertical high permeability pathways during winter months while the lower permeability soils near the land surface remain frozen, thus providing a source of water for aufeis formation. We investigate the effects of the warming conditions on the magnitude and timing of these discharges, which are surrogates for the mass of aufeis and the timing of aufeis formation, respectively. Aufeis formation and ablation are both sensitive to climatic conditions. The sensitivity analyses presented here form a basis for future investigations of aufeis dynamics across the Arctic.