In the ablation zone of land-terminating areas of the Greenland Ice Sheet, water pressures at the bed control seasonal and daily ice motion variability. During the melt season, large amounts of surface meltwater access the bed through moulins, which sustain an efficient channelized subglacial system. Water pressure within these subglacial channels can be inferred by measuring the hydraulic head within moulins. However, moulin head data are rare, and subglacial hydrology models that simulate water pressure fluctuations require water storage in moulins or subglacial channels.
Neither the volume nor the location of such water storage is currently well constrained. We force the model with surface meltwater input calculated using field-acquired weather data. Our first-order simulations of moulin hydraulic head either overpredict the diurnal range of oscillation of the moulin head or require an unrealistically large moulin size to reproduce observed head oscillation ranges.
We find that to accurately match field observations of moulin head, additional subglacial water must be added to the system. This subglacial baseflow is likely sourced from basal melt and nonlocal surface water inputs upstream. We hypothesize that the additional baseflow represents strong subglacial network connectivity throughout the channelized system and is consistent with our small moulin likely connecting to a higher-order subglacial channel.
Trunz, C. The Greenland Ice Sheet is experiencing increased mass loss via surface melting and calving in response to climatic warming Hanna et al. In the ablation zone, most of the seasonal surface melt is routed through supraglacial streams Yang and Smith , ; Pitcher and Smith , that drain into moulins Smith et al. Once meltwater reaches the ice sheet bed, it can change subglacial water pressure, which modulates ice motion.
In this way, spatial and temporal variability in meltwater delivery to moulins can modulate sliding speeds on daily to seasonal timescales. Spatial Banwell et al. The amount, position, and timing of meltwater infiltration into moulins determine local and regional ice motion, which in turn affects global sea-level change Nienow et al. The subglacial drainage system is composed of interspersed efficient and inefficient components Iken et al.
