LOWER THAN PRESENT SEA LEVELS: SEARCHING FOR SUBMERGED SHORELINES IN THE BRITISH ISLES

Sedimentary and geomorphic evidence of former sea levels offers a means to extend the instrumental record of RSL (relative sea level) change. A variety of methods have been applied successfully in saltmarshes and coral reef environments. The former are typically temperate and the latter, tropical features. While very high vertical resolution has been claimed in saltmarsh studies, coral reefs still suffer from low vertical accuracy of sea level indicators. Beachrock offers a much higher-resolution RSL record in the tropics, but is only recently receiving attention in this regard.

Saltmarsh studies are limited by the depth of the marsh and RSL records seldom exceed a few thousand years or a few metres lower than present sea level. In the British Isles, the steep north-south isostatic gradient that resulted from the last British-Irish Ice sheet is evident in late Holocene RSL records. These have proved a useful yardstick for the development of GIA models. A variety of models have been developed that show quite good agreement with the late Holocene observations, but which show significant variation in the late glacial/early Holocene period for which little observational evidence is available.

A regional seismic stratigraphic investigation followed by an intensive coring program was mounted to address this data deficit. Offshore sites with a high potential for preservation of former shorelines were targeted from south to north in the Irish Sea. The results provide insights into the evolution of coastlines and preservation potential of sea level indicators, as well as providing new data on the depth to which sea levels fell in this isostatically active region.