Late Quaternary retreat of the British-Irish Ice Sheet on the continental shelf offshore of NW Ireland.

Traditional reconstructions of the British-Irish Ice Sheet (BIIS) in North-West Ireland, have predominantly been based on terrestrial evidence, and show an ice sheet that did not extend beyond the present coastline. This reconstruction of a restricted ice sheet has, in recent decades, been replaced by that of a more dynamic and extensive ice sheet, which during the Last Glacial Maximum (LGM) advanced to the NW-Irish shelf edge. Investigating the dynamic history of marine-terminating ice sheets is important for a wider understanding of the role that ocean forcing plays in controlling ice sheet advance and retreat.
Multibeam swath bathymetric and acoustic sub-bottom profiler data supplemented by transects of sediment cores across Donegal Bay and the adjoining NW Irish continental shelf were acquired as part of the Irish National Seabed Survey programme and, more recently, the 2014 Britice-Chrono JC106 cruise. These data were used to identify sediment thicknesses, acoustic facies and landforms. Vibro cores from two east-west transects across the shelf have been used to help understand the timing and nature of retreat of this sector of
the BIIS. X-Ray imagery and MSCL scans of the sediment cores have been used along with sedimentological analysis to identify lithofacies associated with the glacial retreat from the shelf. These sediment cores have also been used to ground truth the acoustic facies. Taxonomic analysis of foraminifera from the sediment cores has been used to reconstruct depositional environments. Twenty-one radiocarbon dates from foraminifera and macrofossils sampled from the sediment cores constrain the timing of retreat of the BIIS from the shelf edge to Donegal Bay. Collectively the data confirm an extensive ice sheet, grounded to the shelf edge at the LGM. Radiocarbon dates and lithofacies indicate that initial retreat across the shelf was rapid and occurred in a glacimarine setting, but was punctuated across the mid-inner shelf by stillstands and minor readvances building a series of arcuate moraines.