Sediment Accretion and Recent Sea-level Rise in the Solent, Southern England: Inferences from Radiometric and Geochemical Studies

A detailed radionuclide and geochemical study has been carried out on recent sediments from the Solent estuarine system, Southern England. The vertical distributions of a series of radionuclides (210Pb,137Cs,238Pu,239,240Pu,241Am and60Co) have been examined which provide a measure of the rate of sediment accumulation in Southern England estuaries. The reliable use of radionuclides as indicators of sediment accumulation depends in part on their chemical immobility (lack of redox migration).60Co, in particular, shows evidence for redox mobilization, hence it is essential to use a number of chemically different or inert radionuclides to eliminate possible bias in calculated sediment accumulation rates. While local (intra-estuary) effects influence rates of sediment accumulation, the main control of vertical saltmarsh growth over the Solent area is a rise in mean sea level. Dating of saltmarsh cores indicates a 4–5 mm year−1rise in relative sea level over the last 100 years, in good agreement with tide gauge data. Comparison with data from the literature implies that a recent acceleration in sea-level rise has occurred, from 1•2 mmyear−1to 4–5•5 mm year−1, possibly due to changes in tidal regime or an acceleration in crustal subsidence.