The SOMLIT-Sète station is a part of the French monitoring network SOMLIT (Service d’Observation en Milieu Littoral, https://www.somlit.fr/), accredited by the French Centre National de la Recherche Scientifique (CNRS) as a National Observatory System (SNO). The main scientific objective of the observations at the SOMLIT-Sète station is to assess the long-term impact of climate change and human activities on the coastal Northwestern Mediterranean ecosystem, the impact of potential mid- and long-term changes in continental inputs, as well as changes in the productivity of the Gulf of Lion coastal zone. The SOMLIT-Sète station (latitude 43.3267N, longitude 3.66167E) is located in the dilution zone of a large river, the Rhône, but also small coastal rivers (Vène, Aude, Herault), especially those of the Thau lagoon basin. The SOMLIT-Sète Station is monitored from the Station Méditerranéenne de l’Environnement Littoral (SMEL) of the University of Montpellier in Sète by the staff of the OSU OREME, and the Research Unities of MARBEC (http://www.umr-marbec.fr/en/) and GéoSciences (http://www.gm.univ-montp2.fr/?lang=en). The SOMLIT-Sète station, located on a water-column depth of 30 m, is sampled at the water surface in a bi-monthly frequency. The SOMLIT-Sète station is implemented near an instrumented Cardinal Buoy integrating on the same site two other monitoring systems called SNO COAST-HF (Coastal ocean observing system - High Frequency), and SNO PHYTOBS (Phytoplankton observation network), entitling at site: COAST HF-Sète and PHYTOBS-Sète.

The SOMLIT-Sète is part of the long-term coastal observation stations of the French Research Infrastructure dedicated to coastal ocean observations (Infrastructure de Recherche Littorale et Côtières: ILICO, https://www.ir-ilico.fr).

Bi-monthly collected samples are analyzed for more than 20 core parameters such as temperature, salinity, dissolved oxygen, pH, ammonia, nitrates, nitrites, phosphates, silicates, suspended matter, particulate organic carbon, particulate organic nitrogen, chlorophyll-a, delta¹⁵N, delta¹³C; pico- and nano- plankton; and CTD-PAR-Chla fluorescence profile.

The SOMLIT network quality management system is in line with the ISO/IEC 17025:2017 standard: “General requirements for the competence of testing and calibration laboratories”. Further information on standard operating procedures for sample collection and data acquisition are available at: https://www.somlit.fr/parametres-et-protocoles. For more information on the quality flagging scheme: https://www.somlit.fr/codes-qualite/.