Direct Evidence of Meltwater Flow Within a Firn Aquifer in Southeast Greenland

Within the lower percolation zone of the southeastern Greenland ice sheet, meltwater has accumulated within the firn pore space, forming extensive firn aquifers. Previously, it was unclear if these aquifers stored or facilitated meltwater runoff. Following mixing of a saline solution into boreholes within the aquifer, we observe that specific conductance measurements decreased over time as flowing freshwater diluted the saline mixture in the borehole. These tests indicate that water flows through the aquifer with an average specific discharge of 4.3 x 10(-6) m/s (sigma = 2.5 x 10(-6) m/s). The specific discharge decreases dramatically to 0 m/s, defining the bottom of the aquifer between 30 to 50 m depth. The observed flow indicates that the firn pore space is a short-term (< 30 years) storage mechanism in this region. Meltwater flows out of the aquifer, likely into nearby crevasses, and possibly down to the base of the ice sheet and into the ocean.