Holocene sea levels, Last Glacial Maximum glaciomarine environments and geophysical models in the northern Irish Sea Basin, UK

Newly acquired geological records from the Isle of Man reveal intercalated intertidal and terrestrial sediments that record a relative sea-level rise from ca. - 3.86 m in the early Holocene up to a mid-Holocene maximum between ca. 6.6 and 4.5 cal kyr BP at ca. + 2.25 m. When compared with similar marine records from elsewhere in the northern Irish Sea Basin, the sea-level data confirm a strong north-south trend in glacioisostatic loading, but little east to west difference in loading. This pattern results from the central northern sectors of the British ice sheet over Scotland strongly influencing the glacioisostatic downwarping throughout the northern Irish Sea Basin. Differential ice thicknesses over the Irish Sea, the Lake District and Ireland did not cause perturbations of local glacioisostatic signatures. The Holocene marine data in the central Irish Sea record a slow termination of global eustatic sea-level rise during the early Holocene. Geophysical predictions of relative sea level, partially constrained by the Holocene RSL observations but extrapolated to the Last Glacial Maximum, show the potential for shallow marine conditions in the central Irish Sea Basin and in northeast Ireland between ca. 21.0-16.0 cal kyr BP. However, glaciomarine deposits in northeast Ireland suggest the model relative sea-level predictions are too low, and require increased ice loading or a thinner lithosphere to generate extra glacioisostatic depression at the time of deglaciation. Furthermore, predicted deglacial relative sea level for northeast Ireland does not match the geological record, highlighting complex ice margin/ocean interaction during deglaciation. On the Isle of Man, where glacioisostatic loading is of a similar magnitude to that across northeast Ireland, the presence of grounded ice inhibited marine incursion during early deglaciation, but the occurrence of glaciolacustrine conditions along the ice margin as it moved northwards supports model predictions that relative sea-level fell below present during the Late Glacial/early Holocene due to rapid glacioisostatic rebound. © 2006 Elsevier B.V. All rights reserved.