Marine geophysical evidence for Late Pleistocene ice sheet extent and 1 recession off north - west Ireland 2 3

11 Multibeam swath bathymetry data collected through the Irish National Seabed Survey provides 12 direct evidence for extensive glaciation of the continental shelf off NW Ireland. Streamlined 13 subglacial bedforms on the inner shelf record former offshore-directed ice flow. The major 14 glacial features, however, consist of well developed, nested arcuate moraines which mark the 15 retreat of a former ice sheet margin(s) across the shelf. Distal to these moraines on the outermost 16 shelf prominent zones of iceberg-ploughmarks give way into a well developed system of gullies 17 and canyons which incise the continental slope. The large-scale, nested, arcuate moraines record 18 the episodic retreat, probably punctuated by minor readvances or oscillations, of a grounded ice 19 sheet lobe across this sector of the continental shelf during regional deglaciation. Initial retreat 20 from the outer shelf was associated with an episode of ice sheet break-up and calving as recorded 21 by extensive zones of iceberg ploughmarks distal to the outermost moraine. It is conceivable that 22 this could have been driven by rising sea level. The data indicate a major reorganisation of the 23 Irish Ice Sheet on the NW shelf during deglaciation; an initial elongate ice sheet configuration 24 extending along the shelf edge changed to a pronounced lobate form during retreat. Consideration 25 of dated, marine stratigraphic records from the wider NW margin suggests that ice sheet advance 26 to the shelf edge likely occurred at about 29-27 ka BP, but that retreat from this shelf edge 27 position did not take place until after 24 cal ka BP. Large-scale contrasts in continental margin 28 morphology west of Ireland, from trough mouth fans in the north to gully/canyon systems further 29 to south, reflects a combination of factors including spatial variations in sediment flux related to 30 palaeo-glaciology. 31