NEW CONSTRAINTS ON POST-GLACIAL RELATIVE SEA LEVEL CHANGES FROM ISOLATION BASINS ACROSS NW SCOTLAND

Records of ice sheet demise since the last glacial maximum (LGM) offer insight into the mechanisms that control ice sheet retreat behavior, including sea level (RSL) changes and glacial-isostatic adjustment (GIA) feedbacks. In this study, we investigate RSL changes associated with the retreat of the Minch Ice Stream, a former marine-based ice stream that flowed from the NW sector of the last British Irish Ice Sheet following the LGM. We present new RSL constraints from isolation basin records within the inner Minch of NW Scotland including sites on the Isle of Rasaay and near Fearnmore, Gairloch, and Reiff. Additionally, we use radiocarbon ages from these records to provide constraints on the timing of deglaciation within the inner Minch. We find a marine limit of ~30 m above current sea level at 17-18 ka on the Isle of Raasay, while isolation basins from our other sites record a general decrease in the marine limit northward, to a low of ~9 m above current sea level at 15 ka near Reiff. These results demonstrate that (1) RSL within the inner Minch following the LGM was higher than existing records of RSL show, and (2) the inner Minch became ice-free earlier than previously published cosmogenic-based studies suggest. Our RSL data provide important new constraints for GIA models examining the interactions between marine ice-sheet retreat and post-glacial rebound. Furthermore, our analysis suggests a more rapid retreat of the Minch Ice Stream during the deglaciation than previously thought.