In Situ Measurements of Basal Water Quality and Pressure as an Indicator of the Character of Subglacial Drainage Systems

Abstract

Continuous subglacial measurements of turbidity and electrical conductivity -two indicators of basal water qualitycan be used to help characterize subglacial drainage systems. These indicators of water quality yield information that complements that provided by water pressure measurements. Quantitative attributes of subglacial drainage systems, such as water velocity and subglacial residence time, as well as qualitative behaviour -for example, spatial and temporal variations in system morphology -can be deduced using water quality measurements. Interpretation is complicated by the many potential influences on turbidity and electrical conductivity, but when these complications are appreciated a richer interpretation results. To demonstrate the utility of basal water quality measurements, observations from Trapridge Glacier, Yukon Territory, Canada were examined. The data reveal complex behaviour of the drainage system, but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system. The measurement and interpretation methods described and demonstrated are applicable to other glaciers. As such, they should prove useful for characterizing different subglacial drainage configurations and behaviours, thereby improving our general understanding of the hydrology and dynamics of wet-based glaciers.

Oscillatory subglacial drainage in the absence of surface melt

“…The behaviour of holes A4-A6 is consistent with the behaviour observed on Trapridge Glacier (Murray and Clarke, 1995;Stone and Clarke, 1996) as well as Haut Glacier d'Arolla (Hubbard et al, 1995) and Bench Glacier (Fudge et al, 2008). The sudden switch to showing the same pressure time series as A1-A3 on 4 August indicates that holes A4-A5 become connected to an expanding subglacial drainage system at that time.…”

Modelling water flow under glaciers and ice sheets

“…Measurements of subglacial water pressure [94][95][96][97][98][99], along with the less common measurements of borehole turbidity, electrical properties and geochemistry [100][101][102][103], have also been used to study drainage-system structure and dynamics [103][104][105][106]. Direct visual observations are rare, though borehole imagery [107,108] and exploration of englacial/subglacial tunnels [109,110] and cavities [111] have furnished some important and surprising information [112].…”

A multicomponent coupled model of glacier hydrology 1. Theory and synthetic examples

“…Transitions between these morphologies occur in space and time [e.g., Willis et al, 1990;Stone and Clarke, 1996;Nienow et al, 1998] and are correlated with seasonal variations in glacier flow velocity and ice dynamical instabilities [e.g., Kamb et al, 1985;Clarke, 1987a;Echelmeyer et al, 1987;Fowler, 1987;Kamb, 1987;Raymond, 1987;Harrison et al, 1994;Björnsson, 1998]. …”