Luminescence investigation of sediments from a glaciated alpine catchment

We report initial results from a preliminary study of extraglacial, subglacial and proglacial suspended sediment luminescence at Haut Glacier d'Arolla, Switzerland. The luminescence of suspended sediments evacuated from the subglacial drainage system has the potential to provide important information on the contribution of extraglacial sediments to glacial sediment yields. Since exposure to heat or light modifies the luminescence of sediments, luminescence should vary greatly between extraglacial sediments exposed to daylight and subglacial sediments derived directly from erosion of subglacial bedrock. To assess the potential of this technique, samples collected at ~00:00 hrs over three days during mid-August 2000 comprised: (a) 7 suspended sediment samples from marginal streams that contributed to the subglacial drainage system; (b) 3 extraglacial sediment samples from the main accumulation area; (c) 6 suspended sediment samples from the proglacial stream; and (d) 7 sediment samples from the bases of two boreholes ~100 m deep opened by hot water drilling during mid-July. Sediment samples were prepared in duplicate and subjected to a multiple stimulation analysis (comprising IRSL, OSL and TL) using a Riso DA15 luminescence reader. Initial results demonstrate that despite good reproducibility, surface, marginal and proglacial stream samples show little consistent variation in luminescence signature. However, subglacial samples exhibit consistently low luminescence signatures equivalent to exposure to maximum daily incoming radiation at the glacier surface for over 100 seconds. We conclude that likely errors during sampling are insufficient to account for the degree of bleaching exhibited by subglacial samples, and consider the potential of bleaching due to: (1) transmission of light through glacier ice; (2) transmission of light down boreholes; and (3) glacial grinding.