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


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 dynamic, with re-advance moraines deposited in response to Heinrich Stadial 1. However, these events reflect short-term ice front oscillations (≤ 1 ka) during the long-term retreat phase. Retreat from re-advance positions was synchronous across the range and paced by climate, with time-progressive deglaciation from low to high elevation. In contrast, marked asynchroneity in the timing of Younger Dryas deglaciation is closely linked to snow redistribution and indicates that for small cirque glaciers (≤ 1 km2 ), topography can exert the primary control on glacier survival. This result has important implications for palaeoclimate econstructions as cirque glacier dynamics may be unrelated to 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 prioritise cirque glaciers where snow contributing areas are small and where postdepositional disturbance is limited (matrix-poor, boulder-rich moraines)

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