Physical conditions of fast glacier flow: 1. measurements from boreholes drilled to the bed of Store Glacier, West Greenland
| Autor: | Doyle, SH, Hubbard, B, Christoffersen, Poul, Young, TJ, Hofstede, C, Bougamont, MH, Box, JE, Hubbard, A |
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| Popis: | Marine-terminating outlet glaciers of the Greenland ice sheet make significant contributions to global sea level rise, yet the conditions that facilitate their fast flow remain poorly constrained owing to a paucity of data. We drilled and instrumented seven boreholes on Store Glacier, Greenland, to monitor subglacial water pressure, temperature, electrical conductivity and turbidity along with englacial ice temperature and deformation. These observations were supplemented by surface velocity and meteorological measurements to gain insight into the conditions and mechanisms of fast glacier flow. Located 30 km from the calving front, each borehole drained rapidly on attaining 600m depth indicating a direct connection with an active subglacial hydrological system. Persistently high subglacial water pressures indicate low effective pressure (180 - 280 kPa), with small amplitude variations correlated with notable peaks in surface velocity driven by the diurnal melt cycle and longer periods of melt and rainfall. The englacial deformation profile determined from borehole tilt measurements indicates that 63-71% of total ice motion occurred at the bed, with the remaining 29-37% predominantly attributed to enhanced deformation in the lowermost 50-100 m of the ice column. We interpret this lowermost 100m to be formed of warmer, pre-Holocene ice overlying a thin (0-8m) layer of temperate basal ice. Our observations are consistent with a spatially-extensive and persistently-inefficient subglacial drainage system that we hypothesize comprises drainage both at the ice-sediment interface and through subglacial sediments. This configuration has similarities to that interpreted beneath dynamically-analogous Antarctic ice streams, Alaskan tidewater glaciers, and glaciers in surge. This research was funded by UK National Environment Research Council grants NE/K006126 and NE/K005871/1 and an Aberystwyth University Capital Equipment grant to B. H. A. H. gratefully acknowledges support from the BBC's Operation Iceberg program for the deployment of the GPS reference station and a Professorial Fellowship from the Centre for Arctic Gas Hydrate, Environment and Climate, funded by the Research Council of Norway through its Centres of Excellence (grant 223259). The authors thank the crew of SV Gambo for logistical support, Ann Andreasen and the Uummannaq Polar Institute for hospitality, technicians Barry Thomas and Dave Kelly for assembly of the borehole sensors, Joe Todd for producing a bed elevation model from mass conservation that proved useful in selecting the drill site, and Leo Nathan for assistance in the field. NCEP/NCAR Reanalysis data were provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from www.esrl.noaa.gov/psd/. The data sets presented in this paper are available for download from https://doi.org/10.6084/m9.figshare.5745294. |
| Databáze: | OpenAIRE |
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