Deglacial chronology from County Donegal, Ireland: implications for deglaciation of the British-Irish ice sheet

In the north of Ireland ice advanced northwards onto the continental shelf from inland centres of dispersion at the last glacial maximum. We constrain the timing of three subsequent events by accelerator mass spectrometry C-14 dating of marine microfaunas from muds at Corvish, County Donegal. Early and rapid deglaciation of the continental shelf off northwestern Ireland occurred before 17.1 k C-14 years bp when marine muds formed in Trawbreaga Bay. Ice subsequently readvanced into the bay some time between 15.0 and 14.0 k C-14 years bp and compressed contemporary sea stacks and beach cobbles into a ridge at Ballycrampsey. Early deglacial muds were deformed during this ice readvance and redeposited with stratigraphically inverted C-14 ages between 16.0 and 15.2 k C-14 years BP. The deformed mud is overlain by undeformed laminae deposited during the final deglaciation of the area after 14.1 k C-14 years bp. The early deglaciation in the north at c. 17 k C-14 years bp is correlative with deglaciation recorded in the Irish Sea Basin, western Ireland and northeastern Scotland, indicating a response of the entire British-Irish ice sheet to early warming of the North Atlantic Ocean that resulted in a loss of up to two-thirds of its mass. Subsequent ice-sheet readvance between 15.0 and 14.1 k C-14 years bp in the north is part of a widespread response of the British-Irish ice sheet to Heinrich event I during the Killard Point Stadial. High relative sea levels that accompanied deglaciation at 17 k C-14 years bp and again at 14.1 k C-14 years bp indicate substantial loading and attendant isostatic depression by the British-Irish ice sheet.