MURSYS - North Sea and Baltic Sea - Report 1997

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MURSYS - North Sea and Baltic Sea - Report 1997


Marine Environmental Reporting System - Abstract - Reporting Period: 1 January - 31 December 1997

The summer of 1997 was extraordinarily warm, at mean air temperatures between 8.5 and 9.5 °C. With a yearly precipitation from 460 mm (Kap Arkona) to 660 mm (Elbe estuary), 1997 was the third year in sequence which was too dry. Sea surface temperatures up to 19.4 °C (2.5 K higher than the year before) were measured in the North Sea. Oxygen levels did not fall below critical values at any time.

North Sea:

In the North Sea, phytoplankton showed a typical seasonal development. As in the year before, Coscinodiscus concinnus was dominant. However, the abundance was lower than in 1996. In the North Sylt Wadden Sea, rod-shaped diatoms Rhizosolenia imbricata were very abundant from late June to mid-November. "Black spots" were scarcely observed in the Wadden Sea of Lower Saxony in 1997. Cod, smelt, mackerel as well as haddock have recovered in the North Sea.

Baltic Sea:

In the Baltic Sea significantly raised sea temperatures (about 4.5 k higher than the long-term mean) were measured. In 1997, there was no inflow of salt water. As in 1995 and 1996 the nutrient concentrations were in line with the season. In the deep water of the eastern Gotland Basin hydrogen sulphide was found.
During the past summer, the surface accumulations of blue-green algae were the most extensive and prolonged ones ever recorded in the whole Baltic Sea. A dinoflagellate bloom (Gyrodinium aureolum) with toxic effects on the bottom fauna and fish was observed in September-October in the northern Belt Sea and western Kattegat.
An unusual meteorological situation caused a dramatic flooding event in the Baltic drainage area in summer 1997. Heavy rainfalls led to extreme water levels of the rivers Oder and Vistula. Because of a high load of nutrients local impacts in the Pommeranian Bight occured. These caused oxygen depletion (between Ahlbek and Greifswalder Oie) which influenced the bottom fauna. Long-term effects on the overall Baltic ecosystem are not to be expected.
The stocks of fully developed cod are extremely reduced. However, the cod year-class 1997 is found to be the strongest one in the 1990s. The 1995 flounder year-class hardly reached average size, like the 1993 and 1994 year classes. Dab stocks continued to decline.


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