Seasonally evolving hydraulic transmissivity beneath Greenland supraglacial lakes

Abstract:

Surface meltwater that reaches the bed can lubricate and increase the flow of the Greenland Ice Sheet. Dye-tracing experiments for land-terminating glaciers show that the efficiency of subglacial drainage systems evolves seasonally in response to injection of surface meltwater to the ice-bedrock interface. However, the evolution of subdrainage systems further inland (under ice thicknesses greater than 1000 m) remains largely unknown. Here, we develop a novel method to infer subglacial hydraulic transmissivity based on ice sheet surface uplift relaxation following rapid supraglacial lake drainage events. During a lake drainage event, the injection of water at the ice-bedrock interface creates a water-filled blister, hydraulically raising the ice sheet. Combining field observations with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals subglacial transmissivity. Drainage conditions vary through the melt season, with the uplift relaxation timescale decreasing from 10 days to 12 hours and the lake injection volume increasing by a factor of 5.5, indicating a two-order-of-magnitude increase in subglacial transmissivity. Both seasonal and climate-driven evolutions of the hydraulic transmissivity of inland regions of the ice-sheet bed have the potential to change sliding dynamics of these regions substantially.