New RSL constraints for the Minch from OSL-dated Lateglacial shorelines

Abstract

Past sea levels provide important constraints on global ice volumes, rates of tectonic motion, ice-sheet sea-level feedbacks, and the migration of species through time. Beneath formerly glaciated regions, the marine limit, the maximum extent of sea-levels after glacial retreat, provides some of the oldest post-Last Glacial Maximum (LGM) sea-level constraints. However, although the elevations of marine limits are plentiful, they often remain undated. In this study, we provide new age and elevation constraints on the late Pleistocene relative sea-level (RSL) history at 12 sites along the eastern flanks of the former Minch Ice Stream (MnIS) of northwest Scotland. Optically stimulated luminescence (OSL) was used to date the highest and presumably oldest preserved RSL indicators immediately after ice-sheet retreat. Although slightly older than earlier estimates, our ages confirm the early deglacial age of ∼16.2–19.5 ka for the raised shorelines of northwest Scotland with declining marine limits north of the Isle of Skye from 26.2 ± 4.8 m at Ardaneaskan to 12.8 ± 4.8 m elevation at Achiltibuie, the latter of which lies inside the moraines of the Wester Ross Readvance. Our new OSL ages suggest deglaciation of the MnIS may have been slightly earlier than previously thought, although our large error bars highlight the need for additional age constraints. Our new RSL data provide important constraints for Glacial Isostatic Adjustment (GIA) models for Scotland and shed light on the behavior of the former MnIS, thought to be susceptible to marine ice-sheet instability.