Oscillating retreat of the last British-Irish Ice Sheet on the continental shelf offshore Galway Bay, western Ireland

Louise Callard, Colm Ó Cofaigh, S. Benetti, Richard Chiverrell, Katrien J J Van Landeghem, Margot Saher, Stephen J Livingstone, Chris D Clark, David Small, Derek Fabel, Steven G Moreton

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During the Last Glacial Maximum, the British-Irish Ice Sheet extended across the continental shelf offshore of Galway Bay, western Ireland, and reached a maximum westward extent on the Porcupine Bank. New marine geophysical data, sediment cores and radiocarbon dates are used to constrain the style and timing of ice-sheet retreat across the mid to inner-shelf. Radiocarbon dated shell fragments in subglacial till on the mid-shelf constrains ice advance to after 26.4 ka BP. Initial retreat was underway before 24.4 ka BP, significantly earlier than previous reconstructions. Grounding-line retreat was accompanied by stillstands and/or localised readvances of the grounding-line. A large composite Mid-Shelf Grounding Zone Complex marks a major grounding-line position, with the ice grounded and the margin oscillating at this position by, and probably after, 23 ka BP. The continental shelf was ice-free by 17.1 cal. ka BP, but the ice sheet may have retained a marine margin until c. 15.3 ka BP. Retreat occurred in a glacimarine setting and the ice sheet was fringed by a floating ice-shelf. Collectively, this evidence indicates a dynamic and oscillatory marine-terminating ice sheet offshore of western Ireland during the last deglaciation.
Original languageEnglish
Article number106087
JournalMarine Geology
Early online date26 Nov 2019
Publication statusPublished (in print/issue) - 1 Feb 2020


  • British-Irish Ice Sheet
  • Continental shelf
  • Glacimarine
  • Grounding zone wedges
  • Ice shelf
  • Ice-sheet retreat
  • Last Glacial Maximum


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