Persistent millennial-scale glacier fluctuations in Ireland between 24 ka and 10 ka

We report 80 ¹⁰Be ages on 14 moraines from Irish cirques that show a previously unrecognized signal of at least eight millennialscale fluctuations between 24.5 ± 0.7 ka and 11.0 ± 0.3 ka. Several moraine ages may be correlative with abrupt warming at the onset of the Bølling-Allerød interval (14.7 ka) and the end of the Younger Dryas interval (11.7 ka), suggesting a forced response. Our ages also identify glacier fluctuations that occurred when regional temperatures were relatively stable. This finding is consistent with modeling results showing several hundred-meter-scale glacier fluctuations in response to interannual variability. At the same time, our composite record of cirque-glacier average equilibrium line altitudes (ELAs) shows a response to warming due to increasing greenhouse gases and summer insolation modulated by abrupt climate changes. Our new 10Be chronology thus records both forced and unforced millennialscale glacier fluctuations superimposed on a lower-frequency ELA signal of forced response to climate change.