Meltwater infilltration in the accumulation zone, West Greenland Ice Sheet

Surface meltwater generated in the accumulation zone of the Greenland Ice Sheet (GrIS) will either be retained by refreezing or connect to the glacial drainage system and contribute to annual runoff. The fate of this meltwater is controlled by the infiltration process, which occurs in the presence of subfreezing snow/firnpack temperatures and ice layers. Ice layers are typically treated as impermeable horizons. However, dye-trace observations suggest ice layers do not impede flow but rather accelerate flow by destabilizing the wetting-front, forming preferential flow paths termed pipes. Until the 2008 field season, the permeability of ice layers formed in the snow/firnpack on GrIS was unmeasured. Air permeameter measurements show ice layer permeability to range from 10-15 m2 to 10-12 m2 and firn to be approximately 10-11 m 2. Temperature profile measurements of the snow/firnpack were recorded every 30 min during the 2007 melt season. Temperature profile data confirms piping as a mechanism for meltwater delivery to 10+ m depths at T1 without increasing the full snow/firnpack temperature to 0°C. Meltwater that is piped to the glacier-ice surface can connect to the glacial drainage system and runoff. Current models used to estimate annual runoff from GrIS do not consider the infiltration process; possibly underestimating the actual runoff.