Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 +/- 0.3 mm(3) to 215 +/- 90.2 mm(3)) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

Automated summary

Research on the Greenland Ice Sheet shows that the basal hydrology undergoes significant changes beneath glacier lakes as the melt season progresses. By studying surface uplift relaxation following rapid lake drainage events, researchers have discovered a universal relaxation law that indicates a two-order-of-magnitude increase in subglacial transmissivity. This suggests that seasonal meltwater input drives substantial changes in basal hydrology beneath lakes.