The Baltic Sea

– a unique marine regionostersjon_karta

The Baltic Sea is a large and almost entirely enclosed marine region, located far up in the cold north. It is a brackish sea with both salt and fresh water. The only connection with the ocean is through the Danish straits to the North Sea. Moreover, the Baltic Sea is surrounded by a huge drainage area four times as large as the sea itself, where virtually all terrestrial human activities influence the marine environment. Nine countries are found along the Baltic Sea. Five additional countries are partially located within the drainage area.

Different characteristics from north to south
In the Baltic Sea water flows northwards through the sounds and along the Swedish west coast in the Baltic Current, making Kattegatt and Öresund species rich. When the inflow of salt water through the Danish sounds is sufficiently extensive, the deep areas further north are filled with salty and oxygen rich water. This is a significant occurrence which in recent years has been irregular. It takes approximately one generation for the water in the Baltic Sea to be exchanged. This means that pollutants which are released into the water remain there for a long time. The Baltic Sea is described as a species-poor ecosystem, but the number differs from north to south. The Baltic proper stretches from the waters surrounding Åland to Öresund. It is the marine area which has the most challenging natural conditions and which also is subjected to most pollutants from land, air and sea based sources. Further north, in the Gulf of Bothnia approximately 80 percent of the water is fresh water from the large rivers which flow into the marine area. The marine area is shallow and the body of water is often intermixed from bottom to the surface. It takes approximately four years for the water in the Gulf of Bothnia to be exchanged.

Salinity a determining factor
The Baltic Sea is characterized by its large differences in salinity. From approximately 25 ppm in Kattegatt it decreases to 8 ppm in the southern Baltic Sea, and is down to only 2 ppm in the northern Gulf of Bothnia and in the innermost parts of the Gulf of Finland. The salinity levels influences marine life in a very significant way. Only a few species can live under such differing conditions. The numbers of marine species decrease from more than 1,000 in Kattegatt to only 50 in the Gulf of Bothnia and in the Gulf of Finland, where fresh water species begin to dominate.

Impact of the population
85 million people live within the drainage area of the Baltic Sea. Most live in the southern half, and approximately half reside in Poland. The area is intensely industrialized with forestry operations dominating in the north and agriculture in the south. Nutrients, toxics and other pollutants from land sooner or later end up in the sea, as well as atmospheric pollution. Significant efforts have been made to address the largest point sources. Thereby today’s emissions are dominated by many small, diffuse, sources which collectively constitute the greatest impact on the Baltic Sea.