A dynamic perennial firn aquifer

Abstract:

Ice-penetrating radar and GPS observations are used to reveal a perennial firn aquifer (PFA) on a high icefield in Svalbard. This PFA appears to be fully analogous to those found in Greenland. A bright, widespread radar reflector separates relatively dry and water-saturated firn. This surface, the phreatic firn water table, is deeper beneath local surface elevation maxima, shallower in surface lows, and steeper where the surface is steep. The PFA is recharged by downward percolation of near-surface meltwater, and drained by flow subparallel to ice flow and the glacier surface. The water table of the PFA rises with increasing meltwater supply during summer, especially during warm years, and drops during winter. The reflector cross-cuts snow stratigraphy; we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases. Radar data collected over several years indicate that the PFA responds rapidly (sub-annually) to the surface melt forcing. We use a coupled surface energy-balance and firn model, forced with from regional climate model data for the years 1961-2012, to estimate the amount of retained surface melt available to recharge the PFA. Results suggest that the water amount flowing into and out of the PFA is substantial, such that the PFA is capable of providing significant input to the englacial hydrology system.