Specific Natural Conditions and Their Consequences

State and Evolution ofthe Baltic Sea, 1952-2005, edited by Rainer Feistel, Gunther Nausch, andNorbert Wasmund Copyright 2008 John Wiley Sons, Inc. 

FIGURE 2.1 Difference between precipitation and evaporation (in kg/(m s)) in the area of Europe. The thick grey line around the Baltic Sea marks its drainage basin. (See color plate) 

This positive water balance determines the basic hydrographic and ecological properties of the Baltic Sea as the estuarine circulation, the deepwater formation and ventilation, and the stratification and the nutrient balance. Outflow of brackish surface water and inflow of saline water combined with upwelling and vertical mixing of saline bottom water with brackish surface water closes the estuarine circulation. 

FIGURE 2.2 Schematic picture of the water balance of the Baltic Sea, the water exchange with the North Sea and the transfomiation of water masses in the Belt Sea (bottom left, in river runoff units). 

The inflow of saline water is responsible for the permanent stratification of the central Baltic water body consisting of an upper layer of brackish water with salinities of about 6-8 psu and a more saline deepwater layer of about 10-14 psu. A strong permanent halocline and a thermocline (cf. Fig. 2.2) considerably prevent vertical circulation and, consequently, ventilation of the bottom water aU the year round. 

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