Abstract
This paper describes the historical sea level data that we have rescued from a tide gauge, especially devised originally 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. 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 one hundred years. Changes in sea levels are examined, and previous results revisited with the extended time series. The rate of relative sea level change for the period 1849–2012 is estimated to have been \(1.08\pm 0.04\) mm/year at Marseille, a value that is slightly lower but in close agreement with the longest time series of Brest over the common period (\(1.26\pm 0.04\) mm/year). The data from a permanent global positioning system station installed on the roof of the solid tide gauge building suggests a remarkable stability of the ground (\(-0.04\pm 0.25\) mm/year) since 1998, confirming the choice made by our predecessor geodesists in the nineteenth century regarding this site selection.
Highlights
The main tide gauge at Marseille on the southeast coast of France (Fig. 1) has been maintained since 1885
It was especially devised to accurately define the origin of the French national height system by providing direct measurements of the mean sea level (MSL) through an original recording device designated as a ‘totalisateur’, an ingenious mechanical integrator capable of providing MSL values over specified sampling periods such as a day or week, as described below (Reitz 1878)
A most important part of the tide gauge is the ‘40.500 litres’ copper float of 0.9 m in diameter and 0.2 m in width. It is connected with a pulley mechanism to the recording devices, that is, the pen carriage tracing out the sea level variations on a paper chart and the roller carriage of the ‘totalisateur’
Summary
The main tide gauge at Marseille on the southeast coast of France (Fig. 1) has been maintained since 1885. It was especially devised to accurately define the origin of the French national height system (the ‘Nivellement Général de la France’ or NGF) by providing direct measurements of the mean sea level (MSL) through an original recording device designated as a ‘totalisateur’, an ingenious mechanical integrator capable of providing MSL values over specified sampling periods such as a day or week, as described below (Reitz 1878) Those measurements of MSL taken between February 1885 and December 1896 were used to define the datum for the geodetic levelling of mainland France. The interest for high-frequency sea level data (at least hourly) has been repeatedly expressed by the scientific community (IOC 2012) Within this context, the French mapping agency (IGN) decided to undertake the digitisation of the circa 1200 nine-metre-long tidal charts recorded between 1885 and 1988 and to install a modern acoustic tide gauge in July 1998, providing sea levels at 10-min sampling intervals. The sea level variations since 1849 are revisited based on the updated and extended Marseille time series
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