Holocene land- and sea-level changes in Great Britain

Over the last decade there has been a significant increase in the number and distribution, spatially and through time, of reliable observations of past relative sea level in Great Britain. These have contributed to better models of the glacial isostatic adjustment (GIA) processes at both the national and global scales. Despite significant improvements in the agreement between predicted RSL changes derived from different GIA models and observations from dated sediments there remain important discrepancies. Until the reasons for these are solved, the best estimates of current relative land- and sea-level change come from analysis of the observations, supplemented with estimates from models where there is a good fit. Analysis of more than 1200 sea level index points and 180 limiting dates for 52 locations in Great Britain over the last 16kyr provides estimates of late Holocene land-level changes (negative of relative sea-level change). Maximum relative land uplift occurs in central and western Scotland, 1.6mm/yr, and maximum subsidence in southwest England, 1.2mm/yr. Sediment consolidation, arising from autocompaction as the sediment accumulates and from land drainage, increases the subsidence in areas with thick sequences of Holocene sediments, with an average effect equivalent to an extra 0.2mm/yr land subsidence, but more in parts of southeast England, 0.5 to 1.1mm/yr. Modelled changes in tidal range during the mid to late Holocene in eastern England suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified. The effect is most significant, equivalent to 0.4 to 0.6mm/yr, for large coastal lowlands, the Humber and Fenland, that were tidal embayments during the mid to late Holocene.