MURSYS - North Sea and Baltic Sea - Report 4 2000

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MURSYS - North Sea and Baltic Sea - Report 4 2000


Marine Environmental Reporting System - Abstract - Reporting Period: 1 July - 31 August 2000


North Sea

July had few hours of sunshine and was the first month since January 1999 which was too cold in the entire coastal region (mean values: 14.8 to 15.6 °C). August, too, had moderate temperatures. Due to few rainfalls, it was generally too dry. The mean sea surface temperature in July was 13.4 °C; 15.3 °C was reached in August.
In August, unusual oceanographic conditions were observed in the North Sea: low-salinity Baltic Sea water had penetrated far into the central and northern North Sea. A thermocline developed between the low-salinity warm water and the "heavy" near-bottom cold water.
In late August/early September, nutrient concentrations had their seasonal low. Nitrate and phosphate were largely depleted. Oxygen supply in the deeper layers of the German Bight during the summer was good.
In early July, the abundance of phytoplankton continued to increase. The species diversity in the summer months of July and August was composed primarily of flagellates (Ceratium species, Protoperidinium), diatoms (Coscinodiscus species, Chaetoceros species, Thalassiosira rotula, Guinardia species, Leptocylindrus minimus, Eucampia zoodiacus, Odontella sinensis), armoured dinoflagellates (Prorocentrum species, spiral-type Gyrodinium) and ciliates (Myrionecta rubra). Fewer species of dinoflagellates were found than in the preceding year, and their abundance was generally too low for the season. The number of colonies of the foam-forming alga Phaeocystis globosa and of the microflagellate Chrysochromulina decreased. In July and early August, Noctiluca scintillans still was frequent in some areas.
Potentially toxic Dinophysis were only found at low concentrations. The toxic flagellate Fibriocapsa japonica (area around Sylt) and potentially toxic Chattonella species (around the North Frisian islands) again occurred at low concentrations.

Baltic Sea

With little sunshine and below-average temperatures (15 - 16 °C), July hardly had any summer weather. In August, the monthly mean temperatures of 16 - 17 °C reached average values, but summer days were very rare. On the coasts of Mecklenburg-Vorpommern, precipitation both in July and August was up to 65 % above the mean values. Compared to 1999, little warming of the surface water took place in July. Almost normal values were reached in August.
The mean water level in July was 8 - 14 cm above the reference values. No extreme water levels occurred at the German Baltic Sea coast in August.

In the coastal waters of Mecklenburg-Vorpommern, nutrient levels in August were normal for the season. Hardly any phosphate was measured in the entire sea area. Nitrate occurred only off Boltenhagen and in the Pomeranian Bight at very low concentrations. Silicate levels were normal at most measuring points. In the bottom water of the central basins, phosphate levels increased while nitrite and nitrate values were close to zero because of the poor oxygen situation.

In August, oxygen saturation in the surface water of the western Baltic was close to 100 %. In areas with low water exchange (coastal inlets and bights), only about 10 % saturation was measured in the bottom water. Critical values were found locally.
In spring, hydrogen sulphide was found in deepwater at all stations of the Baltic Proper as well as in the Faeroe and Landsort deeps. Anoxic conditions prevailed below 125 m in the Faeroe and Gotland deeps, below 200 m also in the Landsort deep. The stagnation persisted during the following months in the deepwater of the Baltic Proper.
Compared to 1999, hydrogen sulphide in August increased in the deep areas of the northern Baltic, but decreased in the Bornholm deep.

In July, the phytoplankton development at the coasts of Schleswig-Holstein was characterized by low to medium densities. The most abundant groups were dinoflagellates (Prorocentrum micans, Ceratium tripos, Amphidinium crassum), diatoms (Dactyliosolen fragilissima) and the ciliate Myrionecta rubra. An increase in filamentous blue-green algae was observed in the course of the month.
In early August, the abundance of microalgae in coastal waters decreased from north to south. Cyclotella and Heterocapsa triquetra were found to be more abundant in the Flensburger Förde, while Dactyliosolen fragilissima, Ceratium tripos, and Emiliana huxleyi spread in the Eckernförde Bight. There was a general decrease in filamentous blue-green algae.

In the coastal waters of Mecklenburg-Vorpommern, the chlorophyll concentration was below normal both in July and August. Dinophyceae (Prorocentrum, Gymnodinium, and Heterocapsa), Cyanophyceae (Aphanizomenon "baltica", Woronichinia and Snowella) and small centric diatoms dominated the composition of summer plankton. The typical mass development of Microcystis flos-aquae, which had been observed in the Firth of Stettin in the past years, did not occur this year.


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