Introduction

Abstract

The Baltic Sea¹ is a unique basin of the World Ocean. It is small and shallow, rather a series of basins, and connected to the main Atlantic Ocean only via the Danish Straits (Figure 1.1). The exchange of water through these straits is quite limited, and as a consequence of the positive freshwater balance the Baltic Sea water mass is brackish, with the mean salinity about 7‰—one-fifth of the salinity of normal ocean waters. This elongated sea lies between maritime temperate and continental sub-Arctic climate zones. In winter it is partly ice-covered and during the most severe winters it is completely frozen over. The variable coastal geomorphology and the wide archipelago areas give the Baltic Sea its individual appearance.

The origin of the word “Baltic” is not clear. It may come from “belt” (belt in Germanic languages), a sea shaped like a belt, or “white” (baltas/balts in Lithuanian/Latvian languages).