| Summary: | Optical remote sensing offers a wide range of possibilities for the large-scale, long-term assessment of interacting physical and bio-geo-chemical processes of marginal and enclosed seas. The assessment of environmental features from the vantage point offered by satellites in Earth�s orbit allows to observe at a glance the dynamical relationships of natural setting, water exchanges, basic ecological relations and their main driving forces, as well as the environmental problems faced by regional marine basins. While several sites in the European Seas have been studied in detail and for a long time, others remain surprisingly unexplored. Understanding the inner workings of these seas � aiming to reconcile the conflicting needs of protecting their ecological balance and exploiting their natural resources � requires adequate observation systems, integrating both conventional in situ data gathering techniques and remote sensing techniques. The systematic and synoptic appraisal of surface parameters by means of orbital sensors � like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), used in Figure 1 to give an example of the European Seas features outlined by optical tracers � can help closing some of the existing knowledge gaps.The near-coastal marine regions surrounding the north-western European continent � the Norwegian Sea, the Barents Sea and the White Sea to the north; the North Sea, the Irish Sea, the Celtic Sea, the English Channel, as well as the Bay of Biscay and the Gulf of Cadiz, to the west � can be considered marginal basins of the Atlantic Ocean, where oceanic conditions prevail. Visible imagery of these basins shows a wide spectrum of environmental traits, ranging from those typical of sub-polar regions to others more common in sub-tropical climatic zones. The patterns of water constituents, over the broad continental shelf that constitute most of these basins, suggest that coastal interactions, strong tidal mixing and oceanic currents are the main factors shaping their concentration and distribution. Conversely, in the European enclosed seas, thermohaline conditions are the prevailing environmental drivers of the patterns observed in the visible imagery. The Baltic Sea, the Black Sea and the Caspian Sea are dilution basins, where stratification due to the large freshwater input can prevail, while the Mediterranean Sea is a concentration basin, where vertical convection is strong. The patterns of water constituents indicate the paramount impact of river runoff, particularly in the case of dilution basins, and the key role played by atmospheric forcing in triggering periodic episodes such as exceptional algal blooms, in the concentration basin case.As suggested by these cases, an in-depth analysis of (optical) remote sensing data, and their coupling with information derived from other means of environmental monitoring, can provide clues to help compose the unique mosaic of dynamical and bio-geo-chemical features of the European Seas. JRC.H.3 - Global environement monitoring
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