Helena Alexanderson

Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores. Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 degrees C) the ice-proximal sample showed relatively high doses (similar to 12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 degrees C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 degrees C) doses were overall much higher (similar to 20-55 Gy), which partly is due to a significant (similar to 12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 degrees C) signal. In this Arctic environment it appears that bleaching is limited in the first similar to 100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 degrees C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 degrees C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin. (C) 2012 Elsevier B.V. All rights reserved.