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Abstract: 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 × 10−6 m/s (σ = 2.5 × 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. [ABSTRACT FROM AUTHOR]

A conceptual model, based on field observations and assumed physics of a perennial firn aquifer near Helheim Glacier (southeast Greenland), is evaluated via steady-state 2-D simulation of liquid water flow and energy transport with phase change. The simulation approach allows natural representation of flow and energy advection and conduction that occur in vertical meltwater recharge through the unsaturated zone and in lateral flow within the saturated aquifer. Agreement between measured and simulated aquifer geometry, temperature, and recharge and discharge rates confirms that the conceptual field-data-based description of the aquifer is consistent with the primary physical processes of groundwater flow, energy transport and phase change. Factors that are found to control simulated aquifer configuration include surface temperature, meltwater recharge rate, residual total-water saturation and capillary fringe thickness. Simulation analyses indicate that the size of perennial firn aquifers depends primarily on recharge rates from surface snowmelt. Results also imply that the recent aquifer expansion, likely due to a warming climate, may eventually produce lakes on the ice-sheet surface that would affect the surface energy balance. [ABSTRACT FROM AUTHOR]

We present measurements of the density, hydraulic conductivity, and specific discharge of a widespread firn aquifer in Antarctica, within the Wilkins Ice Shelf. At the field site, the aquifer is 16.2 m thick, starting at 13.4 m from the snow surface and transitioning from water‐saturated firn to ice at 29.6 m. 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 × 10−11 m2. A borehole dilution test indicates an average specific discharge value of 1.9 ± 2.8 × 10−6 m s−1. Ground‐penetrating radar profiles and a groundwater flow model show the aquifer is draining laterally into a large nearby rift. Our findings indicate that the firn aquifer in the vicinity of the field site is likely not in a steady state and its presence likely contributed to past ice shelf instability. Plain Language Summary: Firn aquifers occur in areas of high melt and snow accumulation when meltwater percolates into firn (compacted snow older than 1 year) pore space and is stored throughout the winter without refreezing. In December 2018, a field team traveled to the Wilkins Ice Shelf on the Antarctic Peninsula and drilled into an aquifer. We used a combination of hydrology and ground‐penetrating radar measurements to show that water is flowing laterally through porous buried snow and draining into a nearby rift. 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. Key Points: An extensive perennial firn aquifer within the Wilkins Ice Shelf is characterized for its hydrologic propertiesField data and modeling show the aquifer has high permeability and is flowing into a nearby riftPast disintegration events on the Wilkins Ice Shelf with hydrofracture characteristics are likely a result of the aquifer's presence [ABSTRACT FROM AUTHOR]