Optical dating of sorted circles in King George Island, South Shetland Islands, West Antarctica as a potential time marker for local glacial retreat

Abstract

During the period of deglaciation, the glacier leave moraine sediments behind as they retreat, thus the depositional ages of these sediments provide important information on the timing of glacier retreat (the commencement and the duration of the local deglaciation). However, in some cases, direct dating of moraine sediments is not readily possible because of a lack of suitable materials for conventional dating methods, except where 14C dating is applicable. In addition, optical dating on these sediments has not been successful because moraine sediments usually have little chances of being exposed to sufficient sunlight, which result in significant overestimation in optical ages. The moraine sediments, however, sometimes form a distinctive geomorphic structure, called sorted circles, through repeated freeze-thaw cycles on flat areas in polar regions. In the coarse of its formation, the soil particles above the permafrost layer may move up and down actively (Kessler et al., 2001), and therefore some of these particles are presumed to have chances to be exposed to sunlight sufficiently for the latent luminescence signals to be completely bleached, which is one of the most important prerequisite process for reliable optical dating. To test this, we collected 10 soil samples from 5 sorted circles at the elevations of 37m, 41m, 66m, and 120m in King George Island, South Shetland Islands, Antarctica. Of these samples, two (sample code SC-06, 09) were intensively investigated in this study. Quartz grains extracted from those samples have various undesirable OSL characteristics that cannot be used for routine SAR-based optical dating

The LM-OSL experiments reveal that the quartz OSL signals from both samples are dominated by non-fast OSL components with the medium OSL component being the most predominant signal. In dose recovery tests using a LM-OSL SAR and conventional SAR procedure, the recovered doses were lower than the given dose by 10 % consistently. Thus we