Highlights of the physical oceanography of the Gulf of Finland reflecting potential climate changes

We review highlights of the studies of physical oceanography of the Gulf of Finland, the Baltic Sea, in 1997–2007 that serve, or can be interpreted, as evidence of shifts or changes in the local climate. Also, several findings that can be used as a starting point for studies of climatic changes are described. This time interval starts from the Estonian–Finnish–Russian Year of the Gulf of Finland in 1996, a milestone of joint studies of this area that has separated two worlds since the 1940s. The studies include extensive analyses of historical and recently collected data sets, numerical modelling, and introduction of new theoretical concepts, and cover all basic disciplines of physical oceanography: hydrography, marine optics, marine meteorology, circulation, sea level, waves, and ice conditions. Their output eventually contributed to another milestone — the declaration of the Baltic Sea as a particularly sensitive sea area by the International Maritime Organization in 2005.