Supplementary Data File 5: Luminescence investigations of sediments

Luminescence stratigraphies were generated for the sediments recovered in cores BH2 and BH3 (features 8A and 5A, respectively) following the methods of Kinnaird et al. (2017a; 2017b).

Sampling was undertaken at the core store at the University of Wales Trinity Saint David, Lampeter, between the 3rd and 5th of February 2020. Cores BH2 and BH3 were sampled for OSL profiling and dating. Previously, the cores had been split under subdued light conditions at the University of Warwick, with one-half sampled for preserved sedimentary DNA (sedaDNA), then sedimentological and palaeontological analyses, and the other retained for sampling and OSL screening. The available sedimentological evidence was reviewed, then the cores sampled for OSL screening measurements with portable OSL equipment (Table 5.1; Figure 5.1).

Samples were collected at regular intervals (<10 cm) through the cores, with tighter resolution sampling (2-5cm) around stratigraphic breaks. Profiling measurements were made with portable OSL equipment (Sanderson and Murphy 2010). 4-5 grams of bulk sediment were presented for measurement in 50mm plastic petri dishes. Natural luminescence signals were measured with an interleaved sequence of system dark count (background), infra-red stimulated luminescence and optically stimulated luminescence, similar to that described by Kinnaird et al. (2017a; 2017b). The readout sequence consisted of a 15 s dark count, 2 x 30 s IRSL stimulations, a 15 s dark count, 2 x 30 s OSL stimulations, and a final dark count. The summary files were extracted from the acquisition software, and interrogated in Excel, to calculate dark count rates, IRSL and OSL integrated signal intensities (parameterised here as the gross count over 60 s, minus the backgrounds recorded before and after stimulation), depletion rates (parameterised here as a depletion index comprising the ratio of the net intensity in the first half of the stimulation period to that from the second half) and IRSL/OSL ratios.

These values are shown in Table 5.1 and plotted relative to their position in the stratigraphy in Figure 5.1. This provided the first appraisal of net OSL signal variations within each of the sampled cores, and the means to identify the key temporal breaks and stratigraphic packages within the sedimentary sequences.