Cosmogenic Be-10 chronology of the last deglaciation of western Ireland, and implications for sensitivity of the Irish Ice Sheet to climate change

Accelerator mass spectrometry (AIMS) C-14 slates of fossiliferous marine mud identify a readvance of the Irish Ice Sheet from the north and central lowlands of Ireland into the northern Irish Sea Basin during the Killard Point Stadial at ca. 16.5 cal k.y. B.P, with subsequent deglaciation occurring by ca. 15.0-15.5 cal k.y. B.P. Killard Point Stadial moraines have been mapped elsewhere in Ireland but have previously remained undated. Here, we report sixteen Be-10 surface exposure dates that constrain the age of retreat of the Killard Point Stadial ice margin from western Ireland. Eight Be-10 dates from the Ox Mountains (13.9-18.1 ka) indicate that final deposition of the moraine occurred at 15.6 +/- 0.5 ka (mean age, standard error). Eight Be-10 dates from Furnace Lough (14.1-17.3 ka, mean age of 15.6 +/- 0.4 ka) are statistically-indistinguishable from the Ox Mountain samples, suggesting that. the moraines were deposited during the same glacial event. Given the agreement between the two age groups, and their common association with a regionally significant moraine system, we combine them sir derive a mean age of 15.6 +/- 0.3 ka (15.6 +/- 1.0 ka with external uncertainty). This age is in excellent agreement with the timing-of deglaciation from the Irish Sea Basin (at or older than 15.3 +/- 0.2 cal k.y. B.P.) and suggests the onset of near-contemporaneous retreat of the Irish Ice Sheet from its maximum Killard Point Stadial limit. A reconstruction of the ice surface indicates that the Irish Ice Sheet reached a maximum surface elevation of similar to 500 m over the central Irish Lowlands during the Killard Point Stadial, suggesting a high sensitivity of the ice sheet to small changes in climate.