Late Quaternary glaciation of the continental shelf offshore of NW Ireland

Abstract

The continental shelf offshore of NW Ireland is an area where marine geological and chronological data pertaining to the advance and retreat of the last British-Irish Ice Sheet (BIIS) remains sparse and therefore ice sheet limits are poorly constrained. This is important because well constrained and well dated ice sheet limits are critical to developing accurate ice sheet models representative of the dynamics of the BIIS. The aim of this study is to reconstruct the timing, extent and nature of the last ice sheet advance and retreat across the NW Ireland continental shelf through the sedimentological analysis and radiocarbon dating of marine sediment cores.
A transect of thirteen cores from offshore of Donegal Bay, NW Ireland provide direct evidence for extensive glaciation of the continental shelf. Sedimentological and chronological evidence from the cores indicates that the ice sheet extended to the shelf edge at the last glacial maximum (LGM) and that subsequent retreat from this shelf edge position was underway by 23,700 cal. yr BP. Initial retreat from the shelf edge was rapid and associated with a large calving event. Retreat across the mid shelf was slow and punctuated by the formation of a series of moraines. The ice sheet was likely a grounded tidewater margin in which meltwater contributed strongly to both retreat and glacimarine sedimentation. The ice sheet had attained an inner shelf position, inshore of a prominent moraine in Donegal Bay (the ‘Donegal Bay Moraine’), before 17,800 cal. yr BP, and therefore in contrast to previous work, it is inferred that this moraine pre-dates the Killard Point Stadial. Foraminiferal analysis from two cores (CE-08-003 and CE-08-010) shows the presence of a range of glacimarine taxa associated with ice sheet retreat across the shelf followed by the appearance of warmer Atlantic water taxa later in the cores. Collectively this suggests that ocean forcing did not drive initial retreat from the shelf and it emphasises the role of meltwater during deglaciation of the NW shelf.