The ocean-atmosphere coupling largely shapes the climate of the Earth. Global warming combined with human-induced pressures is now a key driver of environmental changes. The original topography of the Mediterranean sea, a semi-enclosed sea, composed of several sub-basins separated by straits and channels at different depth, makes this sea very sensitive to atmospheric forcing and changes. CIESM findings indicate that Mediterranean water masses have steadily become saltier and warmer in recent decades at all depths and anywhere in the Basin (CIESM WK 16, 2002). All waters (even the deepest) have been acidified since the beginning of the industrial era (Touratier and Goyet, 2011). Slight changes can be evidenced at the surface and in depth and long term observations can provide a wide range of environmental and climatic indicators.

The sea-surface layer is the oceanic boundary region between the ocean and the atmosphere, it plays a vital role in affecting physical and chemical transfers between these two major environmental reservoirs (nutrients, anthropogenic CO2, heat, wind, precipitation, waves, evaporation, etc.). This has important consequences on marine biodiversity, ecosystem functioning and on water circulation. Tracking long-term hydrological and biogeochemical changes across the Basin in surface waters, along coastal and in central zones is required to assess long term variability and to unedrstand the functioning of the Mediterranean Sea. Monitoring of surface waters using buoys, piles and platforms with in situ sensors is very expensive. To overcome this problem, a partnership between scientists, governments and ship companies in different regions of the world allows to take advantage of regular routes taken by ferries and cargoes to keep a "watch" on water features (Figure 1). Automated instrument packages on ships of opportunities are in use since many years, starting form the simple collecting plankton samples during regular ship cruises up to the most recent sophisticated multiparameters box with an ensemble of different sensors and biogeochemical analysers. They allow building time series with a relatively high temporal scale.

The aim of the CIESM PartnerSHIPS programme is to develop a network of ships of opportunity (Figure 2) for automated monitoring of the surface waters of the Mediterranean, using a complex of different physical, chemical sensors to measure the physical and biogeochemical parameters of the Mediterranean (temperature, salinity, oxygen and pCO2, chlorophyll, etc.).
This sea presents one of the more dense maritime traffic in the world, oil tankers, shipping boats, car ferries take many routes across the Basin. A network of ships of opportunity allows a (quasi)synoptic view at the basin scale, not only along the coast but in central zones and in southern/eastern parts of the Mediterranean where the data are missing. Sub-sampled data are sent in real time (via Inmarsat), and contribute to operational oceanography.

Fig. 2     CIESM PartnerSHIPS potential network.