LATE DEVENSIAN AND HOLOCENE SHORELINES OF THE BRITISH-ISLES AND NORTH-SEA FROM MODELS OF GLACIO-HYDRO-ISOSTATIC REBOUND

Sea-level change around the British Isles since the time of the last g lacial maximum is largely due to of the crustal rebound from the glaci al unloading of northern Britain and the concomitant melt-water loadin g of the adjacent seas and Atlantic Ocean. Minor, but not insignifican t, contributions also result from the rebound caused by the unloading of the distant ice sheets, including Fennoscandia and North America. O bservations of sea-level change for this period constrain the glacio-h ydro-isostatic rebound model parameters describing the effective litho spheric thickness or rigidity and the effective mantle viscosity, as w ell as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum. The models permit palaeobathymet ry and palaeoshorelines to be predicted for the British Isles region, including the North Sea, The resulting evolution of the coastlines exh ibits a complex behaviour through time, one that is quite different fr om the usual models in which sea-level change is assumed to be a funct ion of time only. In part this is because of the delayed response of t he mantle to the spatially variable and time-dependent ice and water l oads, and in part because the unloading history of the British ice she et is different from those of the major global ice sheets. Thus, maxim um emergence of the North Sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 (radioca rbon) years BP. During this relative sea-level still-stand shoreline f eatures could have formed, for example, along the western edge of the Norwegian Trough when access to the firths of eastern Scotland would h ave been via a long and shallow marine inlet. Shoreline retreat across the North Sea became relatively rapid after about 10 000 years. The m odel predictions for the Irish and Celtic Seas also suggest a complex behaviour, with the formation of a wide land bridge between about 20 0 00 and 13 000 years ago. The model also suggests that as long as the S cottish ice extended across the northern Irish Sea, until about 14 000 years ago, there would have been a large freshwater periglacial lake located further south. Both the predicted sea-level height-age relatio ns and the shoreline positions are consistent with a large body of obs ervational evidence but some discrepancies occur, particularly in nort hern Scotland and Ireland where the ice heights may have been somewhat greater than assumed in the model.