SNO SOMLIT's "Frioul" station is located in the Gulf of Marseille, with a seawater volume of around 4.4 km3 divided into two basins. The eastern part of the gulf is bounded by the city of Marseille (population approx. 800,000), which stretches from the Nerthe mountain range in the north to the Marseilleveyre massif in the south. This gulf, which is largely open to the sea to the south and west, is characterized by a steep slope and the proximity of one of the most important rivers in the Mediterranean, the Rhône.     It includes the Côte Bleue (land and sea) and the Marseille archipelagos. The Marseilles region is home to Posidonia oceanica meadows, the loggerhead sea turtle (Caretta caretta), cetaceans such as the bottlenose dolphin (Tursiops truncates), and mollusks of Community interest. The Frioul archipelago divides the gulf into two basins of unequal size, which communicate via a sill located between the islet of If and the Pointe d'Endoume. The depth is around twenty meters.

The northern basin, also known as the Marseilles harbor, covers an area of around 65 km², with an average depth of 52 m. It is bordered to the north by the steep slopes of the Nerthe chain, and to the south by the Frioul archipelago. It is bounded to the north by the steep slopes of the Nerthe chain, and to the south by the Frioul archipelago. Along the axis of the Rade, the fairly steep slope at the coast (2.5%) eases off towards the open sea, and the 70 m isobath, which penetrates fairly profoundly into the basin, delimits a vast silted-up plateau no more than 80 m deep.   The southern basin, located between the Marseilleveyre massif and the Notre Dame de la Garde hill, covers a surface area of just 35 km², with an average depth of around 30 m. The gulf's seaward limit corresponds to the 50 m isobath. Also noteworthy is the remarkable regularity of the basin's steepest slope (from 0.6 to 1%), oriented ENE-OSW, which ends well beyond the gulf at depths in excess of 90 m. Since 1995, the SOMLIT-Marseille hydrological quality monitoring program has been operated by the CNRS (French National Center for Scientific Research) to characterize the general state of water masses in the Bay of Marseille at fortnightly intervals, and to assess their evolution in response to climate change.

It is an integral part of the national SOMLIT (Service d'Observation des Milieux Littoraux) network, accredited by INSU/CNRS (https://www.somlit.fr/), which comprises 12 observation stations distributed throughout the French coastline. The station sampled is located in the median part of the Gulf of Marseille, around 5 km from the coast, close to the Frioul archipelago on a sandy bottom, at a depth of 60 m (43.2417°N; 5.29167°E). The initial choice of site was dictated by: its local and regional environmental interest - a strictly marine station, but with a marked continental influence. This point was initially the site of the SOFCOM monitoring program set up in 1994 and has been the subject of much previous work by researchers at the Endoume marine station. Accessibility using the station's own resources allows regular visits and, in the (near) future, automated measurement of certain parameters. It is located off the routes of large commercial vessels. At present, outings are made on board the station ship Antedon II, to carry out the following operations:

• A continuous profile using a multiparameter probe between 0 and 55m.
• Three water samples (surface, maximum chlorophyll, and bottom) for laboratory analysis.

Since January 2009, monitoring of natural isotopic abundances (d15N and d13C) and sampling for pico and ultra-planktonic communities have begun.

Additional measurements or sampling requested by research teams and programs (phytoplankton, zooplankton netting, molecular biology, bio-optical measurements, primary production, etc.).

Some fifteen parameters are measured according to standard procedures accredited by the entire network community. Measurement is carried out in accordance with ISO 17025. SOMLIT-MARSEILLE also collects phytoplankton samples for SNO PHYTOBS. The site is also at the heart of an automated measurement network, combining SNO MOOSE and COAST-HF measurement points. This measurement network constitutes a multi-instrument platform comprising :

• A site for collecting atmospheric deposits and meteorological measurements
• An automatic monitoring station for Rhone River inflows at Arles (SORA)
• A network of sensors between the mouth of the Rhône and the Bay of Marseille
• An instrumented buoy in the Bay of Marseille