IMIS

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:

• To carry out classical process studies, typical of JGOFS
• To focus on small scale biogeochemical processes, in particular at a daily scale.
• To study the influence of nitrogen, phosphorus and iron on oceanic fertility.
• To conduct a calibration/validation operation for the SeaWIFS color sensor.

To reach these objectives, the studied areas as well as the cruise plan had to respond to a number of criteria :

• To investigate different trophic regimes
• To investigate systems characterized by different degrees of limitation in nitrogen and phosphorus
• To study stable ("steady state") systems for a sufficiently long period The cruise track was thus designed to encompass 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. For the particular case of the Moroccan upwelling, the position of the sampling station was not defined a priori but had to respond to two criteria: to be close enough from the upwelling core, here defined as the area with the lowest temperature and the highest pCO2 content to be located in waters deeper than 100 m, i.e. twice the height (50 m) of the mooring (1m2 sediment trap plus carioca buoy) The location was determined using quasi real-time SeaWIFS images to pre-determine an area (actually a rectangle of 1° latitude and 0.5° longitude) while continuous surface acquisition provided a more precise identification of the station location.