Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

Reconstructing the deglacial history of palaeo-glaciers provides vital information on retreat processes, information which can inform predictions of the future behaviour of many of the world's glaciers. On this basis, this paper presents 170 Schmidt Hammer exposure ages from moraine boulders and glacially sculpted bedrock to reveal the post-Last Glacial Maximum (LGM) history of the Wicklow Mountains, Ireland. These data suggest that large ice masses survived for 4–7 ka after retreat of the Irish Sea Ice Stream and were sustained by summit ice fields until ∼16.6 ka. Post-LGM retreat was driven by climate and involved numerous short-term ice front oscillations (≤1 ka), with widespread moraine deposition during Heinrich Stadial 1. In contrast, marked asynchroneity in the timing of Younger Dryas deglaciation is closely linked to snow redistribution which demonstrates the sensitivity of small cirque glaciers (≤1 km²) to local topography. This result has important implications for palaeoclimate reconstructions as cirque glacier dynamics may be (at least partly) decoupled from climate. This is further complicated by post-depositional processes which can result in moraine ages (e.g. ¹⁰Be) which post-date retreat. Future palaeoclimate studies should prioritize cirques where snow-contributing areas are small and where post-depositional disturbance of moraines is limited.