Proglacial hydrochemistry and sediment characteristics observed across a spectrum of glacier dynamic regimes

Abstract:

The broad influence of bedrock geology on glacier dynamics has received comparatively little attention in the alpine glacier literature. Geological influences vary widely from subglacial hydrochemistry to deformable till rheology, which may be governed by the mineralogy and grain size distribution within the till. In an investigation of borehole and proglacial water at an unnamed glacier in the Donjek Range of the St. Elias Mountains, Yukon, Canada, we find that subglacial mineral precipitation exerts a significant control on the proglacial hydrochemistry and suspended sediment flux. To understand if this process is common to glaciers across the range, we collected proglacial water samples from 20 glaciers in and around the Donjek Range. From each sample, we analyzed the hydrochemistry, measured the grain size distribution (GSD) using a Mastersizer laser diffraction particle size analyzer, and analyzed the mineralogy of the suspended sediments using X-ray diffraction. We also analyzed thin sections from bedrock samples collected at the glacier margins to constrain the mineralogical input to the system. This suite of measurements permits us to investigate the discrepancies between the secondary minerals predicted by the proglacial hydrochemistry and the observed mineralogy. Given that glaciers in the sample set exhibit a range of dynamic behaviour (including surging), we investigate how the mineralogy, GSDs, and hydrochemistry vary as a function of glacier dynamics. Where we have identified correlations between surging glaciers and proglacial GSDs, we investigate the possible controls of hydrochemistry and/or mineralogy on the GSDs and thus on subglacial dynamics.