SEA-LEVEL CHANGE ALONG THE FRENCH ATLANTIC AND CHANNEL COASTS SINCE THE TIME OF THE LAST GLACIAL MAXIMUM

Holocene sea-level change along the French Atlantic and English Channe l coast is not uniform because of the response of the crust to the cha nging ice and water loads in Late Pleistocene and Holocene time. The p attern of the spatial variability is a north-south trend, of decreasin g sea levels levels at any time. This results primarily from the isost atic response to the melting of the Fennoscandian ice sheet. Superimpo sed upon this is a mainly east-west trend resulting from the isostatic response of the crust to the addition of the meltwater into the Atlan tic ocean. The combined effect is that at any time sea levels vary spa tially along this coastline by amounts that are predicted to reach 20 m from the time of the Last Glacial Maximum to about 10,000 radiocarbo n yr ago, about 15 m at 8000 yr ago and about 10 m at 6000 yr ago. Thu s observations of past sea levels should not be combined into a single sea-level curve unless first corrected for the glacio-hydro-isostatic factors. Alternatively, the data should only be used to construct reg ional curves for relatively short sections of the coastline, such as P as-de-Calais and Picardie, Normandie, Cotes-du-Nord, Finistere, or the Vendee and Charente-Maritime region. Even within such constrained reg ions the spatial variability may still be of the order of a few meters . Analysis of the observational data by region indicates that major os cillations in sea level are unlikely to have occurred, that levels at no location exceeded the present mean sea level, and that there may ha ve been a small (similar to 3 m) increase in eustatic sea level over t he past 6000 yr. Palaeo-shorelines and palaeo-water depths for the Eng lish Channel and the Atlantic coast shelf have been predicted using th e isostatic and eustatic models and the results indicate that in-situ marine deposits older than 6000-7000 yr are unlikely to be found along many sections of the present coastline.