Constraining the timing of Holocene glacial retreat in Ny-Alesund, Svalbard using quartz optical dating on sorted circle

Abstract

Establishing chronologies on glacier-related sediments is of importance in many studies on climate change because it can provide direct or indirect clues for understanding the timing of local glacier retreat. In periglacial regions, glacier-related sediments such as moraine deposits sometimes form a distinctive geomorphic structure, called sorted circles, through repeated freeze-thaw cycles on flat areas. This structure has a sorted appearance commonly due to a border of stones surrounding finer materials in the inner part of the circles. In terms of OSL dating, the sorted circles are considered to have tow main advantages over other glacigenic sediments: (1) the sediments that comprise the sorted circles have naturally been well-sorted, thus it is easy to collect samples for OSL dating (i.e. easy to insert sampling tube inside the sediment profile without being bothered by pebble- or cobble-sized clasts), (2) According to the model by Kessler et al. (2001), it is implicitly presumed that some portions of the finer grains above the permafrost layer have been exposed to sunlight for prolonged period of time and their OSL signals are well bleached during the formation of sorted circles. If this is the case, the OSL ages of the well bleached finer grains in the inner part of the sorted circles are expected to indicate the minimum age of last local glacier retreat. In this paper, we investigate the possibility of OSL dating of sorted circles using 19 OSL samples recovered from 6 sorted circles in Ny-Alesund, Svalbard, and discuss the potential of sorted circles as an another time marker for local glacier retreat.