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

¹ School of Environmental Science, University of Ulster, Coleraine, County Londonderry BT52 1SA, UK
² Natural Environment Research Council Cosmogenic Isotope Analysis Facility, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK
³ Department of Geosciences, Oregon State University, Corvallis, Oregon 97331, USA
⁴ Department of Geography, National University of Ireland, Maynooth, County Kildare, Ireland
⁵ Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK

Correspondence: E-mail: jorieclark{at}hotmail.com.

Accelerator mass spectrometry (AMS) ¹⁴C dates 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 ¹⁰Be surface exposure dates that constrain the age of retreat of the Killard Point Stadial ice margin from western Ireland. Eight ¹⁰Be 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 ¹⁰Be 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 to 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 ~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.

Key Words: glacial geology • geochronology • cosmogenic dating • Irish Ice Sheet