Using Shear Waves to Characterize a Firn Aquifer on the Helheim Glacier in Southeast Greenland

Abstract

The Greenland ice sheet is melting at an accelerating rate due to increasing global average temperatures. Ice penetrating radar surveys and ice cores extracted from the southeastern margin of the Greenland ice sheet near Helheim glacier discovered that a liquid water aquifer has formed within the near surface recrystallized and compacted snow (firn). Here we use active source seismology to probe the structure of this aquifer in the firn, and present results from a joint inversion technique that uses S-waves, P-waves, and surface waves to constrain the attenuation and seismic velocities that inform on the liquid water stored within the aquifer. Confirming past studies, we find that the aquifer lies at 27.9 +/- 3.5 m and has an approximate thickness of 10 +/- 4 m. We determine there is 1565 +/- 769 kg m-2 of water within the aquifer, a downward revision from past studies. Our study of S-waves and surface waves identified a complex structure in the aquifer layer and future work must incorporate full waveform modeling to use these waves for understanding firn aquifers.