Marine geophysical evidence for ice sheet extension and recession on the Malin Shelf: New evidence for the western limits of the British Irish Ice Sheet

Abstract

Multibeam swath bathymetry and backscatter data collected as part of the Irish National Seabed Survey and Integrated Mapping for the Sustainable Development of Ireland's Marine Resource programmes is used to investigate the glacial geomorphology of the Malin Shelf. The data provides direct evidence that the former British Irish Ice Sheet was grounded as far out as the shelf break in this sector on more than one occasion. Drumlins on the outer shelf indicate the region was a zone of confluence where ice flowing onto the shelf from northwest Ireland converged with ice flowing across the shelf from western Scotland. Ice berg furrows located on the outer shelf record ice sheet break up by a calving event that may have been triggered by rising sea levels and northwest–southeast aligned moraines indicate the ice retreated north-eastwards across the shelf towards Scotland. The absence of direct dating control from moraines on the Malin Shelf precludes a definitive assessment of the timing of ice sheet events. However, consideration of the stratigraphic relationship of the glacial landforms on the shelf with age constrained ice sheet events in the wider region indicates that the former British Irish Ice Sheet reached the outer shelf in this region on at least two occasions during the last cold stage. Moraines that have been overprinted by drumlins may possibly belong to an early phase of glaciation that occurred c 45 ka B. This was subsequently followed by another episode of shelf extensive glaciation where converging ice flow from northwest Ireland and western Scotland reached the shelf break during the LGM that subsequently retreated from the shelf edge around 23 ka BP.