Hydrologic Properties of a Highly Permeable Firn Aquifer in the Wilkins Ice Shelf, Antarctica

Abstract:

Firn aquifers occur in areas of high melt and snow accumulation when meltwater percolates into firn (compacted snow older than one year) pore space and is stored throughout the winter without refreezing. In December 2018 a field team travelled to the Wilkins Ice Shelf on the Antarctic Peninsula and drilled into an aquifer. We present measurements of the density, hydraulic conductivity, and specific discharge of a firn aquifer in Antarctica, within the Wilkins Ice Shelf. At the fieldsite, the aquifer is 16.2m thick, starting at 13.4 m from the surface, with an average density of 850 kg m^-3 and an average ice-layer fraction of 18%. Hydraulic conductivity derived from slug tests show a geometric mean value of 1.4 ± 1.2 ×10^-4 m s^-1, equivalent to permeability of 2.6 ± 2.2 x10^-11 m². A borehole dilution test indicates an average specific discharge value of 1.9×10^-6 m s^-1. A combination of hydrology and ground radar measurements show that water is flowing laterally through porous buried snow and draining into a nearby rift. Additionally a groundwater flow model is used to examine the lateral flow of water through the aquifer into the rift. We find that the firn aquifer near the field site is not likely in steady state locally and its presence likely contributed to past ice shelf instability. Firn aquifers are important since they allow meltwater to be stored at depth, possibly running off into cracks, crevasses, or rifts, and increasing fracture depth, thereby leading to ice shelf destabilization.