Recent decades have seen a degradation of the environmental quality in semi-enclosed seas, which are particularly sensitive to population pressures due to their naturally low flushing rates related to their geometry. The North Sea, Baltic Sea and the Black Sea are amongst the most seriously threatened seas in the Euro-Asian region. Each semi-enclosed sea has a distinct pattern of circulation, transport, mixing, associated with the particular geometry, topography, boundary processes, interior stratification, atmospheric forcing, ice fonnation, straits / sill controls, and the specific inputs...