NAOenvirBaltic.wpd 17.02.2000 DRAFT The North Atlantic Climate Influence on the Baltic Sea Environment

• Main Authors: J. Alheit, A. Lehmann, B. Winterhalter, Andreas Lehmann (physical Oceanography
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Iceland; North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.497.3895; http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/BalticSea.pdf

The prevailing local weather has a direct influence on the Baltic Sea environment. Thus, it is probable that it is also influenced by large scale atmospheric patterns like the North Atlantic Oscillation (NAO).A high NAO winter index, corresponds to an anomalous pressure difference between the Azores high and the Iceland low, resulting in increased westerlies with an increased advection of mild air masses leading to mild winters. A low NAO winter index, corresponds to weak westerlies, with increasing influence by the Eurasian winter high, leading to severe winters in the Baltic Sea. In the present study the influence of the North Atlantic climate, as described by the NAO index, is investigated with respect to its possible impact on biological, chemical and physical conditions prevailing in the Baltic Sea. These variations are compared with the known fluctuations in fish stock and food supply. It is argued that the NAO has an impact on the internal circulation of the Baltic Sea and the water mass exchange with the North Sea, hence, influencing oxic/anoxic conditions in the Baltic Sea deep basins. The study of geological sediment records from the deep basins provides information on the extent and duration of anoxic periods during the recent past, where the NAO index is available, and also during the past millennia to give a proper temporal perspective to variations in Baltic Sea conditions prior to human impact.