MURSYS - North Sea and Baltic Sea - Report 2 2001





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MURSYS - North Sea and Baltic Sea - Report 2 2001

   
 
 

Marine Environmental Reporting System - Abstract - Reporting Period: 1 May - 31 July 2001

 

North Sea

Weather

May was warm and dry, with more sunshine than usual (274 - 298 hours). There was no frost, as in the past year. The monthly mean temperatures ranged between 10.9 °C and 13.3 °C. Precipitation (24 - 51 mm) was below average.
June was less sunny than the preceding month (175 - 220 hours of sunshine). At mean temperatures between 13 °C and 14 °C, it was too cold. Rainfalls were frequent and occasionally heavy (93 - 138 mm precipitation).
July had typical summer weather, except in the second third of the month (monthly mean temperatures 17.4 °C - 18.9 °C; 230 - 296 hours of sunshine).

Water temperatures

While in May an above-average water temperature of 9.3 °C was recorded, June was below average, at 11.7 °C.
The surface water mean temperatures in July, reached 15.3 °C, respectively, which was above the climatological values.
The temperature difference between the warm surface layer and the deep water of the North Sea in July / August exceeded 12 °C in some places, which means that this year the North Sea water has stored less heat than usual and will cool down more quickly as soon as the autumn storms set in.

Phytoplankton

In the northern Sylt Wadden Sea, the spring bloom of diatoms was followed by a minor Phaeocystis bloom reaching its maximum in mid-May. During the whole period, the species spectrum was dominated by diatoms and dinoflagellates. While the number of diatom species decreased slowly, an increase in dinoflagellate species was observed. The dominant species was the foam-forming alga Phaeocystis globosa (early May) and the diatom Cerataulina pelagica (early June).
Off Helgoland, Cerataulina pelagica, Leptocylindrus minimus and Pseudo-nitzschia were the prevailing diatoms. Among flagellates, an increase in Raphidophyceae was observed.

An unseasonably early second bloom of the foam-forming alga Phaeocystis globosa, with exceptionally high cell concentrations of over 7000 cells/litre, occurred near Norderney in mid-June, causing strong foam formation on the beaches. Major developments of larger diatom species were not observed.
West of Sylt, the chain-forming diatom Cerataulina pelagica was most abundant in June. In the Schleswig-Holstein coastal waters, Dinophysis norvegica, Protoperidinium punctulatum, and Torodinium robustum were ubiquitous; also tube-shaped and Odontella diatoms were present.
Near Helgoland, accumulations of the autotroph ciliate Myrionecta rubra and many small colonies of the foam-forming Phaeocystis globosa were observed toward the end of the month. The abundance of plankton increased.

Near Norderney, increasing numbers of jellyfish were found stranded on the beaches from mid-July. The main species was the dark brown striped compass jellyfish (Chrysaora hysoscella).

Phytoplankton in the North Sylt Wadden Sea showed a relatively normal development in July. Only few of the typical seasonal dinoflagellate species were observed (Diplopelta bomba, Noctiluca scintillans). Diatom species prevailed (Actinoptychus senarius, Bellerochea malleus, Cylindrotheka closterium, Guinardia delicatula, Lithodesmium undulatum, Odontella rhombus). The group of Chaetoceraceae was present with the largest number of species, which is typical of the season. Only single occurrences of potentially toxic species were reported.
The typical seasonal Noctiluca development in the high seas off Helgoland occurred very late this year. Extensive areas of the sea showed an impressive dark red discoloration caused by the autotroph ciliate Myrionecta rubra.
Near the North Frisian islands, colonies of foam-forming algae (Phaeocystis globosa) were quite abundant. Northwest of Sylt, colonies of foam-forming algae as well as diatoms (Cerataulina pelagica, Skeletonema costatum) were observed.
The calm and very warm summer weather at the end of July led to the expected formation of orange-coloured algal mats, so-called "red tides", caused by mass developments of the luminescent dinoflagellate Noctiluca scintillans in the German Bight.

Baltic Sea

Weather

May was warm (11.3 - 13.1 °C), sunny (300 - 323 hours of sunshine) and mostly dry. Precipitation was generally low (21 - 40 mm), with only a few strong rainfalls and thunderstorms.
At mean temperatures between 13.4 °C and 14.5 °C, June was too cold (about 200 hours of sunshine). It rained frequently, and some thunderstorms brought heavy rain (up to 109 mm). Summer weather did not set in until the end of the month.
July was a typical summer month: very warm (18 - 19 °C), very dry (30 - 40 mm rain) and sunny (250 - 310 hours).

Water temperatures

Warmer weather in May caused a continuous warming of the water. A thermal stratification forming in the Mecklenburg Bight became stronger in June.
Due to the exceptionally warm weather in July, water temperatures along the coast of Mecklenburg-Vorpommern were 2 K too high on average.
Also the bottom water in the shallow, unstratified water body between Warnemünde and Ahlbeck was clearly too warm, over 4 K above normal (July: 7.9 - 19.1 °C).

In May, surface temperatures in the Baltic Proper reached 5 - 8.5 °C. Temperatures in the intermediate layer, at 3.5 - 4 °C, were relatively high.
In July, the temperatures were far above the long-term mean values (19.8 - 20.7 °C). The thermocline was at 17 - 18 m depth. The calm and sunny weather led to the formation of a second thermocline at a depth of 8 m.

Water levels

In May (494 - 499 cm), the situation was balanced without any extreme events.
At 457 cm, the lowest water level was recorded in Flensburg in June.
In July, the water level curves (501 - 505 cm) generally showed the typical calm development of the season. The values were slightly below the reference series.

Salinity

In May, due to the increased influx of freshwater in spring, salinity in the surface layer (4.3 - 11.6) was about 1 lower than the month before. Accordingly, the outer coastal waters including the bottom water had salinities which were 1 to 2 below normal in almost all areas. In the inner coastal waters, the salinity (1.3 - 12.7) had hardly changed from the preceding month.
The values in June were generally normal or slightly below normal.
Surface water salinity (July: 7.4 - 9.9) was seasonably low along the entire coast. Inflowing high-salinity water from the Belt Sea led to salinity increases in the bottom water (July: 7.6 - 23.8).

Phytoplankton

May: At the "Seebrücke Heiligendamm" monitoring station, the silicoflagellate species Dictyocha speculum which has been observed since mid-April continued to increase in abundance until mid-May. Diatoms (Attheya decora), dinoflagellates (Glenodinium sp.) and Myrionecta rubra occurred as well. Toward the end of the month, Cryptophyceae developed again.

In the outer coastal waters of Mecklenburg-Vorpommern, chlorophyll-a concentrations were low. Only in the eastern regions of the Pomeranian Bight where 165 to 700 % higher-than-normal biomass levels recorded, as in the preceding months. Plankton in these areas was rich in species and individuals (Teleaulax acuta, Asterionella formosa, Diatoma elongatum, and Stephanodiscus cf. neoastrea), while phytoplankton concentrations along the other outer coasts were low.
In the inner coastal waters, elevated chlorophyll-a concentrations were measured in the eastern areas, as in the preceding months. In the Firth of Stettin, phytoplankton was rich in species and individuals (cryptoflagellates, diatoms).

In the firths and bays of the Baltic coast of Schleswig-Holstein, the pattern of microalgae development was quite different in June. In the waters of Kieler Innenförde, a clearly visible red water discoloration caused by the ciliate Myrionecta rubra was observed. Various small flagellates prevailed in the waters of Flensburger Innenförde. The abundance of diatoms (Dactyliosolen fragilissimus, Proboscia alata) increased towards Schlei and Aussenförde.
In the second half of June, the plankton composition was very uniform and was dominated by diatoms. In the innermost parts of Flensburger Förde and Kieler Förde, the typical seasonal June bloom of Skeletonema costatum was observed. Myrionecta rubra as well as the above diatom species still occurred in these areas.

Also in early July, diatoms prevailed in the firths and bays of the Baltic coast of Schleswig-Holstein. In the innermost parts of Kieler Förde, the seasonal diatom bloom (Proboscia alata) continued. In the harbour area of Eckernförde, the abundance of Myrionecta rubra and of a microflagellate (Eutreptiella marina) increased. Only few diatoms were observed in the other sampling areas. Naked dinoflagellates (Gymnodinium estuariale) were found everywhere at low densities.
While chlorophyll-a concentrations in the western coastal waters of Mecklenburg-Vorpommern exceeded the long-term monthly mean (LMM) by up to 200 %, the LMM was not reached in the Pomeranian Bight. Average chlorophyll-a levels were measured in the inner coastal waters. Phytoplankton in almost all areas was dominated by small flagellates, i.e. by undetermined Chrysophyceae as well as Pseudopedinella, Plagioselmis, Hemiselmis, Tetraselmis, and Teleaulax.

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