193 Marine/Coastal Science

Tuesday, 29 October 2013
8:00 AM - 12:00 PM
Mile High Ballroom 3C

NEW POSTGLACIAL RELATIVE SEA-LEVEL CHANGE RECORDS FROM THE BRITISH AND IRISH CONTINENTAL SHELF

Paper number: 193-4
Program: Technical Sessions
Time: 8:45 AM – 9:00 AM

Authors

Abstract

The pattern of relative sea-level (RSL) change around the British Isles shows marked spatial variability in response to ice sheet history and crustal response to loading/offloading. The area thus offers an ideal natural laboratory for the investigation of such interactions and has formed the basis of several models of earth-ice-ocean interaction. Data with which to test models is, however, largely restricted to the late Holocene for which period many RSL curves have been derived from salt marsh studies. There is a paucity of data from much lower than present sea levels and this is reflected in large (tens of metres) discrepancies between different modelled RSL curves for the late-glacial early Holocene period, despite close agreement of the models for the mid-late Holocene. Few data currently exist that can resolve these discrepancies.

We have just completed two years intensive fieldwork on six sites around the Irish Sea (at Bantry Bay, Waterford, Cardigan Bay, offshore Louth, Isle of Man, and Belfast Lough) on a north-south gradient. These were selected to target lower than present sea-level indicators from ice-proximal to ice-distal locations. The initial investigation using multibeam bathymetry and shallow seismic profiling identified several sea-level indicators including wave-cut platforms and associated cliffs in bedrock, planation surfaces on drumlins, incised valley termini and terraces and the depth of the transgressive unconformity (and in some cases its seaward terminus). Subsequent coring of seabed targets yielded over 450m of core from 150 sites. The most consistently identified RSL indicator at all sites was the transgressive unconformity. It was penetrated in cores at most sites and has yielded age-dateable material. Palaeoenvironmental interpretation and radiocarbon dating of material is ongoing, but has already yielded new observational data on lower than present sea levels with which to test model simulations. Initial findings point to a lowstand off southern Ireland of -75m compared to a lowstand off Northern Ireland of -30 to -40m. The implications for understanding earth-ice ocean interactions will be discussed.