FIRN AQUIFER STRUCTURE IN SOUTHEASTERN GREENLAND FROM ACTIVE SOURCE SEISMOLOGY

For the past decade, perennial storage of water has been observed in the firn of the southeastern Greenland ice sheet, a region of both high snow accumulation and high melt. The aquifer is created through percolation of surface meltwater downward through the firn, saturating the pore space above the ice-firn transition. Our team carried out a series of active source seismic experiments using refracted seismic waves to recover the depth, velocity, and number of layers that describe the firn and aquifer structure. Combining the seismic detection of the aquifer base with a radar sounding of the water table situated at the top of the firn aquifer, we are able to quantify the volume of water present. We find the base of the aquifer lies on average 27.7±2.9 m beneath the surface, with an average thickness of 11.5±5.5 m. Using a Wyllie average for porosity, we found the aquifer has an average water content of 16±8%, with considerable variation in water storage capacity along the studied east-west flow line, 40 km upstream of the Helheim glacier terminus. Here we present new results from the modeling of S-wave and attenuation structure within the aquifer. Elucidating the volume of water stored within these recently discovered aquifers is vital for determining the hydrological structure and stability of the southeastern Greenland ice sheet.