Initial In-situ Hydrologic Measurements of the Greenland Perennial Firn Aquifer

Widespread storage of meltwater within the compacting snow (firn) in the southeastern region of the Greenland ice sheet exists throughout the year. The water saturated firn (~10-30 m below the snow surface) extends to an average depth of 20 m and overlays the firn-ice transition. The aquifer resides mainly within the percolation zone at elevations between 1200 and 2000 m, in areas of high snow accumulation. Depth specific hydrologic measurements in several boreholes within the Greenland ice sheet firn aquifer are used to understand water recharge, transport, and discharge, as well as the aquifer's relationship with the broader englacial drainage system. Measurements within the aquifer (~20-30 m below the snow surface) include hydraulic conductivity, water levels, and environmental tracer concentrations in the liquid water (tritium, CFCs, and noble gasses). Tritium concentration profiles (from the surface to ~50 m depth) were also measured in firn core above, within, and below the aquifer. Similarities and differences to land-based groundwater aquifers are observed. Slug and aquifer pumping tests indicate high hydraulic conductivity (~10-4 m/s). Water samples show minor differences in tritium variation with depth and larger difference in dissolved noble gasses with depth. Tritium concentrations at depth in water and firn are similar to each other but differ from predicted concentrations based on a core-derived firn depth-age model and tritium decay. CFC concentrations are lower than atmospheric solubility. Tritium and CFC results suggest that exchange between liquid water and the atmosphere is very different in this firn aquifer than a conventional groundwater aquifer. These first of their kind measurements taken from the Greenland perennial firn aquifer contribute to our understanding of aquifer behavior and it's relation to regional ice-sheet dynamics and contribution to sea-level rise.