COMPACTION OF HOLOCENE STRATA AND THE IMPLICATIONS FOR RELATIVE SEA-LEVEL CHANGE

The contribution of compaction of Holocene strata to sea-level rise, shoreline erosion and wetland loss is difficult to decipher because of a lack of long-term empirical data. We analyze more than 360 radiocarbon-dated index points to constrain relative sea levels along the east coast of England during the Holocene and to provide estimates of sediment compaction. The isostatic effect of glacial rebound explains regional-scale differences in relative sea levels. North East England, the most northerly study area, reveals a mid to late Holocene high stand, <1 m above present at ~3–4 k.y. B.P., whereas the Tees Estuary, Humber Estuary, Lincolnshire Marshes, Fenlands and North Norfolk each reveal sea-level histories of an upward trend during the Holocene. Within each area, sediment compaction explains the variation in elevation between sea-level reconstructions derived from index points taken from basal peat and those from peat intercalated within thick sequences of Holocene sediments. We find average compaction rates of 0.4 ± 0.3 mm yr^-1 with higher values for the large estuaries. Rates of late Holocene relative sea-level changes, calculated from basal peats, range from -0.2 ± 0.1 mm yr^-1 (i.e., sea-level fall) in North East England to 0.8 ± 0.1 mm yr^-1 in North Norfolk. Inclusion of intercalated index points overestimates late Holocene rates by 0.1–0.4 mm yr^-1 because of the effects of sediment compaction.