Rapid thinning of the Welsh Ice Cap at 20–19 ka based on 10Be ages

Abstract

New 10Be ages from the summits of three mountain areas of North Wales reveal a very similar exposure timing as the Welsh Ice Cap thinned after the global Last Glacial Maximum. Eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19.08±0.80ka (4.2%, 1σ). Similar exposure ages over a 320m vertical range (824 to 581m altitude) show that ice cap thinning was very rapid and spatially uniform. Using the same production rate and scaling scheme, we recalculated six published 10Be exposure ages from the nearby Arans, which also covered a similar elevation range from 608 to 901m and obtained an arithmetic mean of 19.41±1.45ka (7.5%, 1σ). The average exposure age of all 15 accepted deglaciation ages is 19.21±1.07 (5.6%, 1σ). The complete dataset from North Wales provides very strong evidence indicating that these summits became exposed as nunataks at 20–19ka. This result provides important insight to the magnitude of ice surface lowering and behavior of the Welsh Ice Cap during the last deglaciation that can be compared to other ice masses that made up the British-Irish Ice Sheet.