Resolving discrepancies between field and modelled relative sea-level data : lessons from western Ireland

Accurate reconstruction of Lateglacial and Holocene relative sea-level (RSL) histories is complicated where mismatches exist between geological data and RSL curves generated by models of glacio-isostatic adjustment (GIA). In Ireland, such discrepancies have profound implications for interpreting the glacial history of the British Isles and for the use of glacial rebound models to predict future sea-level changes. To address this issue we present new RSL data from four sites along the western coast of Ireland, including 17 data points from the critical period before 5000 14C a BP for which very few data are available. We generate new RSL simulations from an existing GIA model, incorporating a thickened Irish Ice sheet component. Simulated curves from Co. Mayo and Co. Donegal accommodate the higher than present Lateglacial RSL inferred from glaciomarine muds while still meeting the requirement for below present RSL indicated by the new terrestrial limiting data points. Relaxation of trimline constraints on maximum ice sheet thickness provides considerable scope for improved GIA performance. These results demonstrate inferences about RSL drawn from GIA modelling and glacio-sedimentary data are not mutually exclusive, and represent a significant step towards resolving a long-standing debate between the field-based and modelling communities.