Using In-Situ Seismic Measurements to Model the Velocity Structure of Subsurface Aquifers in Southeast Greenland

Abstract:

In 2011, a perennial storage of water in the firn was observed in southeastern Greenland. An aquifer is created by surface melt water percolating down through the firn and saturating the pore space above the firn-ice transition. The mean depth to the top of the aquifer is 15 m and where it has been measured is 25 m thick. This water remains in the liquid state throughout the entire year and is stored within the aquifer. The firn aquifer contribution to sea level rise remains unclear. The aquifer could supply water to the glacier bed, accelerating glacial flow in the region. The aquifer could also store water until a saturation point is reached, and if the water is released at once, it could supply large amounts of fresh water to the ocean. To quantify the amount of liquid water stored in the firn, we used refraction seismic profiles to probe the base of the aquifer in 3 separate locations on the southeastern Greenland ice sheet. Finding the total thickness of the aquifer allows us to calculate the volume of water stored in the firn over these 100-500 meter long refraction lines. Our refraction seismic approach is sensitive to the thickness of the firn aquifer and total water content stored in the pore space of the firn. We combine our seismic measurements with densities and porosity data taken from firn cores extracted in the same area, as well as magnetic resonance soundings, and ground penetrating radar profiles to further constrain the structure of 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.