Surface melt produces more mass loss than any other process on the
Greenland Ice Sheet. In some regions of Greenland with high summer
surface melt and high winter snow accumulation, the warm porous firn of
the percolation zone can retain liquid meltwater through the winter.
These regions of water-saturated firn, which may persist for longer than
one year, are known as firn aquifers, commonly referred to as perennial
firn aquifers. Here, we use airborne ice-penetrating radar data from the
Center for Remote Sensing of Ice Sheets (CReSIS) to document the extent
of four firn aquifers in the Helheim, Ikertivaq, and Køge Bugt glacier
basins with more than six repeat radar flight lines from 1993 to 2018.
All four firn aquifers first appear and/or show decadal-scale inland
expansion during this time period. Through an idealized energy-balance
calculation utilizing reanalysis data from Modèle Atmosphérique
Régionale (MAR) regional climate model, we find that these aquifer
expansions are driven by decreasing cold content in the firn since the
late 1990s and recently increasing high-melt years, which has reduced
the firn’s ability for refreezing local meltwater. High-melt years are
projected to increase on the Greenland Ice Sheet and may contribute to
the continued inland expansion of firn aquifers, impacting the ice
sheet’s surface mass balance and hydrological controls on ice dynamics.