Unveiling firn hydrological processes in Greenland’s percolation zone with continuous radar monitoring

The Greenland Ice Sheet (GrIS) is losing mass at accelerating rates, currently contributing ~25% to global mean sea-level rise. About half of this mass loss stems from surface melting and runoff into the ocean. In the accumulation zone, firn can buffer surface meltwater runoff, but this capacity is constrained by available pore space and presence of impermeable ice layers. As surface melting intensifies with climate warming, the future ability of firn to mitigate runoff remains uncertain, largely due to limited understanding of firn hydrological processes.

Here, we present results from autonomous phase-sensitive radio-echo sounders (ApRES) deployed at three sites in the GrIS percolation zone: KAN-U, Dye-2 and Camp Century. Installed in spring 2023, the instruments collected hourly data throughout the year, capturing the summer melt season. We analyze the ApRES time series to infer firn-meltwater interactions in the near-surface, including changes in water saturation, downward percolation of meltwater, and ice layer formation. This study demonstrates the potential of autonomous radio-echo sounding to monitor firn hydrology and provides new insights to improve predictions of firn evolution under a warming climate.