MURSYS - North Sea and Baltic Sea - Report 4 1998

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MURSYS - North Sea and Baltic Sea - Report 4 1998


Marine Environmental Reporting System - Abstract - Reporting Period: 1 August - 15 September 1998


The mean temperature in August was about 16.0 °C. The last decade of the month was unusually cold, with daily mean temperatures reaching only 15.0 °C. September had the lowest number of sunshine hours on record since the beginning of regular weather data measurements.

North Sea

The water column in August warmed up less than last year (mean sea surface temperature: 14.7 °C (-0.3 K). Oxygen saturation in the German Bight at the end of August was 97 % at the water surface, and 90 - 97 % near the bottom. Nutrients were largely depleted, as is normal for the season.
Microplankton showed a wide variety of species along the entire German coast. Low cell concentrations of diatoms, flagellates and ciliates, with diatoms prevailing, were found. The abundance of Noctiluca continued to decrease, from 1000 individuals/ L in mid-August to 1 - 28 individuals/ L in early September. Potentially toxic Dinophysis were observed at low concentrations around Helgoland and the North Frisian islands in mid-August, and in early September also between Baltrum and Langeoog and in the Jade. The fish toxic flagellate Fibrocapsa japonica was found in harmless concentrations in the area of the North Frisian islands and the East Frisian coast.

Baltic Sea

In early August, the water temperature near the surface, at about 16.5 °C, was 3.5 K below that recorded last year. Until mid-September, the temperature continued to decrease to 14.6 °C. Nutrient concentrations were seasonally low. This year, oxygen levels west of Darss Sill were also good in the bottom water, reaching up to 60% of saturation. In the inner area of Flensburger Förde, hydrogen sulfide was found in the bottom water at 0.5 m above the bottom. Hydrogen sulfide levels increased in deep water of the Bornholm Basin, eastern Gotland Basin and Faroe Deep.
In August and early September, diatoms were abundant mainly in the inner areas of the bays and inlets. Concentrations of dinoflagellates decreased clearly, except in the outer coastal waters of Mecklenburg-Vorpommern, where the dinoflagellate species Prorocentrum, Dinophysis, and Ceratium prevailed. From the beginning of August, filamentous blue-green algae of the species Aphanizomenon, Nodularia, and Anabaena increased in abundance but started to decline as early as September. A longer lasting accumulation of blue-green algae at the surface was only observed in the Gulf of Finland, where mass developments of the common jellyfish Aurelia aurita and of the water-flea Cercopagis pengoi, an alien species introduced from the Caspian Sea, were observed.


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