Environmental Observatory of the Littoral (EOL) biogeochemical data from the Northwestern Mediterranean sea.

The EOL (Environmental Observation of the Littoral) buoy is operated since 2013 in the bay of Villefranche-sur-Mer (France, 43°40'54.0"N 7°19'10.8"E). This buoy (3.6 m wide, 4 tonnes), equipped with solar panels, allows performing, in an autonomous way, measurements of physico-chemical parameters on a mooring mode (2.5 m depth). This buoy was developed as part of a partnership between the Observatoire Océanologique de Villefranche (OOV; now Institut de la Mer de Villefranche, IMEV) and the company Mobilis. Data transmission is performed on a daily basis and data stored on a server on land (http://www.obs-vlfr.fr/data/view/eol/surface/). The buoy is currently involved in the COAST-HF network as part of the Coastal Ocean and Nearshore Observation French Research Infrastructure (ILICO). In particular, the buoy is equipped with a Sea-Bird SBE SMP-ODO deployed at the surface (2.5 m). An extra CTD is available in order to rotate during calibration at the manufacturer. Underwater cleaning of the sensors is performed on a monthly basis. In addition, a proper cleaning in the lab is performed three times a year. The site where the buoy is deployed is visited (100 m away from the buoy) on a weekly basis as part of the SOMLIT network. In the framework of SOMLIT, casts are performed with a CTD properly cleaned after each use and calibrated on a yearly basis. Salinity data from the buoy are corrected based on these extra-measurements. Furthermore, discrete sampling is performed for the measurements of oxygen (Winkler method) in order to inter-calibrate the respective sensors on the buoy.