Climatic factors in the Atlantic control the oceanographic and ecological changes in the Baltic Sea

Salinity changes in the Baltic Sea have been attributed to a lack of balanc e between irregular pulses of North Sea water penetrating the Danish Strait s and the freshwater runoff to the Baltic Sea. Both guises and runoff are c ontrolled by climatic factors in the Atlantic. The occurrence of major puls es of oceanic water has proved unpredictable, being nonexistent during the 1980s. We used dynamic regression models to relate the response of the Balt ic Sea salinity to hypothetical controlling factors: westerly winds, freshw ater runoff, and, ultimately, the Northern Atlantic oscillation (NAO). Our results provided evidence for general chain-of-events relationship between the NAO and a subsequent weather effect over the North Sea, which was final ly extended to the Baltic Sea salinity. Westerly winds followed changes in the NAO with a lag of <1 month. Total freshwater runoff to the Baltic Sea f ollowed changes in the NAO with a lag of <2 months. Furthermore, the salini ty responded to freshwater runoff with a time lag of <1 yr, and a significa nt decreasing trend was found in the salinity series. On the basis of the e xisting lags, we foresee a possibility to predict not only oceanographic, b ut also biological interactions in the Baltic Sea.