Millennial-scale fluctuation in Ireland’s cirque glaciers during the last deglaciation.

Abstract:

During the last deglaciation (20ka -11ka), variations in the Atlantic Meridional Overturning Circulation (AMOC) caused centennial-to-millennial abrupt climate change. Because of Ireland’s proximity to North Atlantic deep-water convection sites, changes in climate associated with variations in the AMOC would be particularly pronounced there, and are recorded by fluctuations of the Irish Ice Sheet. Many of Ireland’s mountains also hosted cirque glaciers, which would have been particularly sensitive to abrupt climate changes of the last deglaciation. Dating of cirque glacier moraines with cosmogenic nuclides can provide a millennial-scale reconstruction of variability in these highly sensitive cirque glaciers. We report 29 ¹⁰Be ages from five cirque basins across western and southern Ireland. Two moraines, one inner and one outer, at Lough Accorymore on Achill Island have ages of 17.04 ± 0.31 ka and 18.43 ± 0.79 ka, respectively, and complement an age of 18.53 ± 0.68 ka from a cirque moraine directly adjacent to Accorymore. All three moraines are Oldest Dryas in age and suggest variability during the millennial-scale Clogher Head Stadial in Ireland. Two moraines in counties Mayo and Donegal suggest deglaciation during the Bølling-Allerød interval with ages of 13.81 ± 0.14 ka and 13.92 ± 0.46 ka, respectively. Two separate moraines in Donegal and Mayo have ages of 11.77 ± 0.44 ka and 11.79 ± 0.47 ka indicating deglaciation following the Younger Dryas stadial in western Ireland. A site located in the MacGillycuddy’s Reeks in County Kerry returned ages of 26.53 ± 0.62 ka and 20.70 ± 0.18 ka on outer and inner arcuate moraines, respectively.