Quantifying meltwater refreezing along a transect of sites on the Greenland Icesheet

On the Greenland ice sheet, a significant quantity of surface melt water refreezes within the firn creating uncertainty in surface mass balance estimates. This refreezing has the potential to buffer seasonal runoff to future increases in melting, but direct measurement of the process remains difficult. We present a method for quantifying refreezing at point locations using in situ firn temperature observations. A time series of sub-hourly firn temperature profiles were collected over the course of two melt seasons from 2007 to 2009 along a transect of 11 sites in the accumulation zone of Greenland. Seasonal changes in temperature profiles combined with heat flux estimates based on high temporal resolution temperature gradients, enable us to isolate the heat released by refreezing using conservation of energy. Our method is verified from winter data when no refreezing takes place, and uncertainty is estimated using a monte carlo technique. Results provide additional evidence of a significant amount of refreezing taking place at depths greater than 1 m and that runoff begins to occur above the ELA. Near the runoff limit, lateral migration of melt water significantly complicates the relationship between total surface melt and total refreezing.