Glacial and glacially-related features on the continental margin of northwest ireland mapped from marine geophysical data

Abstract

Despite over a century of research, reconstructions of the western margin of the last British-Irish Ice Sheet remain controversial. This is mainly because the ice sheet extended offshore onto the continental shelf and therefore significant portions of the glacial record are below present sea level. The availability of high resolution multibeam swath bathymetric and geophysical sub-bottom data for over ∼30,000 km2 of the northwest Irish continental margin (between 55°40́ and 54°18́ N, and 7°50́ and 11°4́ W) has made it possible to map glacial features on the continental shelf and glacially-related features on the continental slope and rise. The resulting map, presented here at a scale of 1:260,000, shows that the major glacial features consist of subglacial bedforms and nested arcuate moraines of different orientations across the width of the shelf. Distal to these moraines, the outermost shelf and upper slope are crossed by subparallel and cross-cutting furrows created by iceberg scouring and meltwater discharge at the ice margin. A well-developed system of gullies and canyons and frequent escarpments incise the continental slope. Several large depositional lobes, likely related to the delivery of vast amount of sediment at the ice margin are found in inter-canyon areas and at the base of the slope. Collectively these data show an extensive ice sheet margin across the entire shelf and sedimentation on the continental margin was greatly affected by the presence of the ice margin at the shelf edge.