The PROSOPE (PROductivity of Oceanic PElagic Systems) cruise took place from the 4th of September (Agadir, Morocco) to the 4th of October (Toulon, France) 1999 aboard the RV Thalassa. There were four main scientific objectives: 1, carry out classical process studies, typical of the Joint Global Ocean Flux Study (JGOFS), 2, focus on small scale biogeochemical processes, in particular at a daily scale, 3, study the influence of nitrogen, phosphorus and iron on oceanic fertility and 4, conduct a calibration/validation operation for the SeaWIFS (Sea-viewing Wide Field-of-View Sensor) color sensor.

To reach these objectives, the studied areas, as well as the cruise plan, were designed : To investigate different trophic regimes, to investigate systems characterized by different degrees of limitation in nitrogen and phosphorus and to study stable ("steady state") systems for a sufficiently long period.

The cruise track encompassed a variety of trophic systems ranging from eutrophic conditions associated to the Moroccan upwelling to the typical ultra-oligotrophic conditions of the eastern Mediterranean sea during summer stratification.

Two main types of stations were occupied :

• 9 short (4-hour) stations. These sites were occupied around the solar noon and were essentially designed to conduct objectives 1 (JGOFS process studies) and 4 (SeaWIFS validation/calibration)
• 3 "long" (5-day) stations, where all four objectives were investigated with a particular emphasis on objectives 2 (processes at a daily scale) and 3 (nutrient resources and oceanic fertility).

Between each station, continuous multiparametric (hydrological, optical, biological and chemical) surface acquisitions were performed.