AMS C-14 dating of deglacial events in the Irish Sea Basin and other sectors of the British-Irish ice sheet

Sedimentary sequences deposited by the decaying marine margin of the British-Irish Ice Sheet (BIIS) record isostatic depression and successive ice sheet retreat towards centres of ice dispersion. Radiocarbon dating by accelerator mass spectrometry (AMS) of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation, enabling us to evaluate the dynamics of the BUS and its response to North Atlantic climate change. Here we use our radiocarbon-dated stratigraphy to define six major glacial and sea level events since the Last Glacial Maximum. (1) Initial deglaciation may have occurred >= 18.3 kyr C-14 BP along the northwestern Irish coast, in agreement with a deglacial age of similar to 22 Cl-36 kyr BP for southwestern Ireland. Ice retreated to inland centres and areas of transverse moraine began to form across the north Irish lowlands. (2) Channels cut into glaciomarine deglacial sediments along the western Irish Sea coast are graded to below present sea level, identifying a fall of relative sea level (RSL) in response to isostatic emergence of the coast. (3) Marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10-15 m similar to 16.7 C-14 kyr BP that flooded the Irish Sea coast and may have triggered deglaciation of a marine-based margin in Donegal Bay. (4) Intertidal boulder pavements in Dundalk Bay indicate that RSL similar to 15.0 C-14 kyr BP was similar to present. (5) A major readvance of all sectors of the BIIS occurred between 14 and 15 kyr (14) C BP which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins. This event, the Killard Point Stadial, indicates that the BUS participated in Heinrich event 1. (6) Subsequent deposition of marine muds on drumlins 12.7 C-14 kyr BP indicates isostatic depression and attendant high RSL resulting from the Killard Point readvance. These events identify a dynamic BIIS during the last deglaciation, as well as significant changes in RSL that reflect a combination of isostatic loading and eustatic changes in global sea level. (c) 2005 Elsevier Ltd. All rights reserved.