Extent, timing and nature of retreat of the
British-Irish Ice Sheet offshore of
north-western Ireland during and following
the Last Glacial Maximum

Abstract

Abstract
There has been a long history of research that has attempted to reconstruct the extent and dynamics of
the British-Irish Ice Sheet (BIIS) during the last glacial cycle. Early reconstructions of ice extent in Ireland were based on terrestrial evidence, and advocated a relatively restricted ice sheet during the Last Glacial
Maximum (LGM) that did not cover the whole of the island. More recent investigations from the continental
shelf around Britain and Ireland reveal evidence for a much larger ice sheet, confluent with the Fennoscandian
Ice Sheet in the North Sea and extending westwards onto the Atlantic continental shelf. However, offshore
chronological control on the timing of ice sheet advance and retreat remain poor for many sectors of the
continental shelf, particularly west and north-west of Ireland.
This thesis brings together high-resolution multibeam swath bathymetry, sub-bottom proler data, and
sedimentological, micropalaeontological and geochronological data, in order to reconstruct the extent, timing and dynamics of the last ice sheet in Donegal Bay and the adjoining north-western Irish continental shelf.
This area is of interest due to its location adjacent to the North Atlantic and the Gulf Stream branch of the
thermohaline circulation, making this sector of the BIIS sensitive to external forcing. The new data in this
thesis show evidence for the extension of a grounded ice sheet to the shelf edge at or shortly after 26.3 cal ka
BP, and thus during the LGM. Foraminiferal assemblages and lithofacies show that subsequent retreat took
place in a glacimarine environment, and acoustic stratigraphic data show that the retreat was characterised by several still stands and re-advances, creating a series of arcuate moraines across the shelf. Chronological data constrain initial retreat from the shelf edge to before 24.8 cal ka BP, with formation of a large moraine at the mouth of Donegal Bay dated to between 20.2 and 17.9 cal ka BP.
The results and interpretations presented in this thesis thereby offers a new interpretation of the extent,
timing and nature of the north-western sector of the BIIS, offshore of Donegal Bay and across the adjacent
continental shelf, during the LGM and the subsequent deglaciation.