A ¹⁰Be-dated record of glacial retreat in Connemara, Ireland, following the Last Glacial Maximum and implications for regional climate

Late Pleistocene stadials are traditionally viewed as periods of severe, year-round cooling centred on the North Atlantic, where the abrupt onset and termination of stadial conditions is widely, though not unequivocally, thought to reflect the impact on Atlantic Meridional Circulation of meltwater fluxes from fringing ice masses. Widespread subaerial melting of land-based ice, however, implies a state of glacier-climate disequilibrium that, according to some conceptual models, had to persist for the duration of each stadial event rather than immediately prior to it. Yet, to date, the spatial extent of any such melting remains unclear, as do the magnitude and duration of any cognate atmospheric warming. To help address this ambiguity, we reconstructed the timing and nature of deglaciation of the Connemara ice centre, Ireland, which, being located immediately downwind of the North Atlantic, affords an ideal location for assessing terrestrial expressions of stadial and non-stadial conditions. We report 15 new cosmogenic beryllium-10 ages of glacial erratic boulders that reveal the timing and magnitude of fluctuations in this sector of the former Irish ice sheet during Heinrich Stadial 1 (HS1). Coupled with geomorphic mapping, these results indicate rapid, widespread deglaciation of the Connemara ice centre at approximately 17 ka, under full stadial conditions, and that the ice margin retreated back to regional source areas rather than eastward towards the centre of the island. Recognising the potential divergence from the traditional view of cold North Atlantic stadials, we propose that the rate and nature of deglaciation in Connemara during HS1 likely reflects enhanced subaerial melting during the summer ablation season.