Abstract

Abstract. Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modeling with results strongly dependent upon assumptions with poor observational constraints. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or nonexistent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains manyfold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying that a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in western Greenland.

Highlights

  • The flow speed of the outer flanks of the Greenland Ice Sheet (GrIS) typically exhibits distinct seasonal (e.g., Zwally et al, 2002) and diurnal (e.g., Shepherd et al, 2009) variations that can be doubling to tripling. Both observational (e.g., Andrews et al, 2014) and modeling (e.g., Schoof, 2010) studies have established a close association between the speed changes and evolving subglacial hydrologic conditions forced by surface melt

  • This study examines the role of basal meltwater generation in subglacial drainage system characteristics in the ablation zone of western Greenland

  • We focus on the Isunnguata Sermia outlet basin and on the winter months when surface melt is minimal to nonexistent

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Summary

Introduction

The flow speed of the outer flanks of the Greenland Ice Sheet (GrIS) typically exhibits distinct seasonal (e.g., Zwally et al, 2002) and diurnal (e.g., Shepherd et al, 2009) variations that can be doubling to tripling. Both observational (e.g., Andrews et al, 2014) and modeling (e.g., Schoof, 2010) studies have established a close association between the speed changes and evolving subglacial hydrologic conditions forced by surface melt. While the phenomenon appears to be common to glaciers and ice sheets, the driving processes are unclear, with regards to in situ observations of bed conditions

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