Hydrographical investigations in the Baltic Sea area before the founding of ICES

Few investigations exist from the Baltic Sea from the 1700s. Many scientists speculated on the changes in sea level in the Baltic Sea. T. O. Bergman analysed surface waters and some scientists measured density and water temperature. In the early 1800s, Forchhammer carried out chemical analysis of samples from different sea areas, including the Baltic. He confirmed Marcet’s statement on the constant relation between chemical elements in seawater. Several other scientists analysed seawater samples chemically. Salinity determinations using chemical methods and density measurements were carried out by Danish, Finnish, German, Russian, and Swedish scientists. Two important expeditions were carried out in the Baltic Sea, the first in 1871 by the German “Pommerania" and the second by the Swedish “Alfhild” and “G. a f Klint” in 1877. The deep circulation and stagnation of the Baltic deep water were explained using the results from these expeditions. International cooperation between the Scandinavian countries and Germany was established. Hydrographical methods and results are described and discussed. Hydrographical tables for salinity determination using density measurements were published by Ekman, Makarov, Krümmel, and others at the end of the 1800s.