Sea-Level Change in the Irish Sea since the Last Glacial Maximum: Constraints from isostatic modelling

Abstract

Models of glacio-hydroisostatic sea-level change have been published for the British Isles that are broadly consistent with the observational evidence, as well as with glaciological constraints. It has been argued, however, that the models fail to represent sea-level change along the Irish Sea margins and in southern Ireland for the post-deglaciation period. The argument rests on the interpretation of the depositional environment of the elevated 'Irish Sea Drift' on both sides of the Irish Sea: whether this is terrestrial or glaciomarine. The isostatic models for the British Isles are consistent with the former interpretation in that sea-levels on either side of the Irish Sea, south of about the Isle of Man, are not predicted to have risen above present sea-level at any time since the deglaciation of the Irish Sea. This implies that ice over both the Irish Sea and Ireland was relatively thin (ca. 600-700 m over Ireland). If the glaciomarine interpretation of the elevated Irish Sea Drift is correct, then the maximum ice thickness over central and southern Ireland would have to reach 2000 m, exceeding that over Scotland. Furthermore, for the resulting sea-level change to be consistent with the Holocene evidence, this thick ice sheet could not have extended to the eastern side of the Irish Sea. Nor could it have been very thick at its northern and western limits. If such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the Irish Sea Drift as terrestrial in origin.