IN SITU COSMOGENIC 10Be AND 14C: A WINDOW INTO PAST ICE SHEET THICKNESS IN SCOTLAND AND IRELAND

The British-Irish Ice Sheet (BIIS) is one of the best-constrained paleo-ice sheets in the world, with detailed geomorphological and geochronological data constraining margins and retreat patterns. Despite this, the thickness of this former ice sheet remains uncertain. High elevation locations offer potential for constraining former ice sheet thickness; however, a lack of glacial erosion due to cold-based ice cover of mountain summits limits the use of single isotope cosmogenic exposure dating, as inherited nuclides commonly yield ages older than the last glaciation from mountain top landscapes. As such, landscapes that experienced cold-based ice cover and those at relatively high elevations are underrepresented in glacial reconstructions, both for the BIIS and globally, thus negatively affecting their ability to serve as training datasets for numerical models used to reconstruct paleo-ice masses. Here, we use paired ¹⁰Be/¹⁴C extracted from bedrock and boulder samples in high-elevation locations across Scotland and Ireland. Our multi-nuclide approach uses one long-lived nuclide, ¹⁰Be, and one short-lived nuclide, ¹⁴C, allowing for an examination of two questions: 1) What is the vertical pattern of deglaciation across the BIIS? 2) Did mountaintops exist as nunataks during the last glaciation? To address these questions, we collected samples from one site in Scotland (Cairngorm Mountains) and four Irish mountains (Dublin, Wicklow, and Mourne Mountains, as well as Mt. Brandon in Dingle) for paired ¹⁰Be and ¹⁴C analysis, yielding 22 new pairs of exposure ages. At four of our study sites, ¹⁰Be results yield exposure ages preceding the LGM, indicative of a lack of erosion during the last glaciation or prolonged exposure. Our ¹⁴C results show concentrations at or near secular equilibrium at three of those sites, indicating either exposure during the last glaciation or a period of glaciation too short for inherited ¹⁴C to decay. These results provide insight into ice-mass thinning and the spatial pattern of glacial erosion, allowing for a more holistic view of cryospheric change in the region in response to a changing climate.