. Operational forecasting of ocean circulation and marine ecosystem fluctuations requires multi-parametric real-time measurements of physical and biochemical prop¬erties. The architecture of a system that is able to pro¬vide such measurements from the upper-thermocline layers of the Mediterranean Sea is described here. The system was developed for the needs of the Mediterranean Forecasting System and incorporates state-of-the-art sensors for optical and chemical measurements in the upper 100 m and phys-ical measurements down to 500 m. Independent moorings that communicate via hydro-acoustic modems are hosting the sensors. The satellite data transfer and the large auton¬omy allow for the operation of the system in any open-ocean site. The system has been in pre-operational use in the Cre¬tan Sea since January 2000. The results of this pilot phase in¬dicate that multi-parametric real-time observations with the M3A system are feasible, if a consistent maintenance and re¬calibration program is followed. The main limitations of the present configuration of M3A are related: (a) to bio-fouling that primarily affects the turbidity and secondarily affects the other optical sensors, and (b) to the limited throughput of the currently used satellite communication system.