Reconciling Subglacial Drainage Patterns on the Western Greenland Ice Sheet

Abstract:

The development and configuration of the subglacial hydraulic system under the ablation zone of the western Greenland Ice Sheet (GrIS) modulates seasonal surface-melt-driven perturbations in ice surface velocity. Following the onset of the summer melt season, elevated ice velocities gradually decrease, suggestive of inefficient drainage transitioning to an efficient channelized drainage system. This ice velocity pattern is observed throughout much of the ablation zone; however, recent work suggests that the development of ice-incised subglacial channels may be limited at higher elevations. This apparent incompatibility has yet to be extensively explored. In order to examine the role of subglacial channelization in determining the seasonal ice velocity pattern, we compare GPS-derived ice surface velocities from 2011 and modeled subglacial channel development using moulin locations, supraglacial melt production, and realistic ice and bed conditions from the Paakitsoq Region of the GrIS. In particular, we focus on the duration of early melt season high-pressures and associated elevated ice velocities. We find that in near-terminus regions, the duration of modeled high pressures agrees with high GPS-observed ice velocities. Farther inland, this relationship weakens, suggesting that the observed deceleration may not be solely driven by subglacial channelization and is instead driven by other mechanisms. Our results also suggest that seasonal surface ice-velocity patterns are not solely indicative of local transitions in subglacial drainage between distributed and channelized networks.