Rescue of the historical sea level record of Marseille, France, from 1885 to 1988, and its extension back to 1849-1851

This poster describes the historical sea level data that we have rescued from an original tide gauge especially devised for geodesy. This gauge was installed in Marseille in 1884 with the primary objective of defining the origin of the height system in France. Hourly values for 1885-1988 have been digitized from the original tidal charts. They are supplemented by hourly values from an older tide gauge record (1849-1851) that was rediscovered during a survey in 2009. The quality of both recovered data sets have been critically edited for errors and their reliability assessed. The hourly values are thoroughly analysed for the first time after their original recording. A consistent high-frequency time series is reported, increasing notably the length of one of the few European sea level records in the Mediterranean Sea spanning more than hundred years. Changes in sea levels are examined and previous results revisited. The rate of relative sea level change for the period 1849-2011 is estimated to 1.07 +/- 0.12 mm/yr at Marseille, a value which is in very close agreement with the longest time series of Brest over the same period (1.27 +/- 0.12 mm/yr). The data from the permanent GPS station installed on the roof of the solid tide gauge building suggests a remarkable stability of the ground (0.04 +/- 0.20 mm/yr) since 1998, confirming the appropriate choice made by our predecessor geodesists in the 19th century regarding this selection criterion.