January was too mild, at monthly mean temperatures between 0.5 and 3.7 °C. Precipitation, partly as snow, reached only 50 to 75 % of the reference values. Also February, at mean temperatures between 1 and 3 °C, was about 1 K too warm and contributed to the generally too mild winter season. Precipitation in February, at 40 to 60 mm, was 10 to 70 % above the long-term monthly mean values. It snowed repeatedly.
Although meteorology counts March as the first month of spring, wintery temperatures prevailed this year. At monthly mean temperatures between 1.5 and 2.0 °C, it was 0.5 to 1 K too cold.
April was relatively mild, at mean temperatures between 6 and 8 °C. Precipitation was up to 50 % above normal. There were some days with snow. April like the three preceding months, had few hours of sunshine.
The mean sea surface temperature in January was 7.1 °C, and 6.2 °C in February, exceeding the climatological value in both months. Average values were reached in April, at 6.6 °C.
The winter of 2000/2001 again was a weak ice winter, with relatively little ice formation in the German coastal waters. This is the fourth consecutive winter with a below-average ice extent.
In the North Sylt Wadden Sea, phytoplankton in the first months of 2001 was characterized by the typical winter species; 73 different diatom species and 20 dinoflagellate species were observed. The genera Thalassiosira and Odontella were relatively frequent, as were Chaetoceros species.
This year's spring bloom was dominated by the diatom Odontella aurita. Since late March, also the foam-forming alga Phaeocystis globosa has been observed. At the end of April, this alga was quite frequent, constituting the dominant plankton species.
Near Norderney, the foam-forming alga Phaeocystis globosa reached its maximum abundance in mid-April. At the same time, the largest bloom of the diatom Odontella sinensis was observed. Late April/early May also marked the beginning of the growth period of the bioluminescent alga Noctiluca scintillans.
On the whole, the species composition of phytoplankton showed the normal seasonal pattern.
The monthly mean temperatures in January, which ranged from 0.7 °C to 2.2 °C, were 1 to 2 K above the long-term means of 1961 - 1990. Precipitation was low, at 20 - 30 mm, and remained 25 - 50 % below the reference values. Snowfalls were rare.
Also in February, the monthly mean temperatures, at values between 1 and 2 °C, exceeded the long-term mean values by 1 - 2 K, making the winter of 2000/2001 generally too mild. Precipitation ranged between 20 and 40 mm. At the beginning of the month and from 23 February, precipitation fell as snow (snow cover 8 - 12 cm thick). Sunshine was more frequent than usual, at 84 to 110 hours, and exceeded the long-term monthly mean by 30 to 60 %.
March was characterized by wintery weather. At monthly mean temperatures between 2 and 3 °C, the values were about 0.5 K below the reference values. Although temperatures in April were clearly below average for two weeks, it was generally too mild, at mean temperatures between 5.5 and 7.5 °C. Rainfalls were 10 to 80 % above normal. Some snowfalls occurred as well. Only 120 to 130 hours of sunshine were recorded in most areas, which was 20 - 30 % below normal.
In the coastal waters of Mecklenburg-Vorpommern, water temperatures in the first two months of the year exceeded the reference values.
The bottom water of the western Mecklenburg Bight showed positive departures of about 4 K in January, 2 K in February, and 2.4 K in March. Vertical temperature differences were weak. In the inner coastal waters, temperatures in the surface layer were about normal.
Inflowing maritime polar air in April led to water temperatures which were 3 - 4 K too low along the entire outer Baltic coast (3.7 - 7.3 °C). The water body still was well mixed.
The water temperatures in the surface layer in February were very high (3.3 - 4 °C), especially in the Baltic Proper (1 - 2 K above the mean values). Above-average temperatures were also measured in the bottom water (4.7 - 8.8 °C).
In March, temperatures of 2 - 3 °C were measured in the surface layer, and 4 - 8 °C in the bottom water.
In January, high-pressure influence prevailed. The water levels (496 - 501 cm) were close to normal, without major fluctuations.
Highly variable wind directions in February had varying effects on the water levels. The measured values (494 - 498 cm) were 9 cm (Schleswig-Holstein) to 12 cm (Mecklenburg-Vorpommern) below the reference series.
A NE storm over the western Baltic in mid-March led to water levels 1 m above normal. The highest water level was measured in Lübeck, at 635 cm. Water levels in March generally were 3 - 12 cmcm above the reference series.
In April (495 cmcm), the water levels differed 5 - 8 cm from the reference values.
In March, nearly normal values were measured in the outer coastal waters of Mecklenburg-Vorpommern, while in the inner coastal waters the salinity was just below normal.
In April, slightly elevated salinity values (6.1 - 13.3) were measured in the surface layer of the Mecklenburg Bight; salinity in the other Baltic areas was slightly below normal.
The salinity of the bottom water (6.9 - 20.5) between Boltenhagen and Buk was up to 4.7 higher than normal, and was slightly too low in the other sea areas. A vertical salinity gradient occurred only in the western Mecklenburg Bight. The salinity in all inner coastal waters was about normal (1.1 - 12.7).
In February, low salinities were measured in the surface water of the Baltic Proper at almost all stations (6.3 - 8.3); they were below the long-term average. Salinities in the bottom water were normal (9.2 - 16.5).
Deepwater salinities in the eastern Gotland Basin in May were 11.5 to 12.1, in the western Gotland Basin 9.6 to 10.4. In the Bornholm Deep, values between 15 and 16.3 were measured.
At the German coasts, the winter of 2000/2001 again was a weak ice winter with comparatively little ice formation. This is the fourth winter in series with a below-average ice extent.
In the northern Baltic, the ice extent in mid-January corresponded to the normal ice development at the beginning of December. Intensive ice formation did not begin until early February due to an inflow
of cold air. The ice formation process, which was interrupted by mild weather in mid-February, led to the formation of a complete ice cover in the eastern Gulf of Finland and northern Gulf of Bothnia.
In early March, the ice cover reached its first maximum. The northern part of the Gulf of Bothnia and nearly the entire Gulf of Finland were covered by ice.
In the Gulf of Finland and in the southern part of the Bay of Bothnia, the normal seasonal decrease of ice was observed in early April. In mid-April, the Gulf of Riga was completely free of ice. In late April/early May, the ice situation improved further, and restrictions to shipping in the Bottenvik harbours could be partially lifted. The 2000/01 ice season ended for two Finnish icebreakers.
At the monitoring station "Seebrücke Heiligendamm", the phytoplankton biomass in winter was low. From the end of January, growth has been observed of the phototropic ciliates Myrionecta rubra, the Cryptophyceae Teleaulax sp., and several Bacillariophyceae (diatoms). In mid-February, the Euglenophyceae Euteptiella sp. started to develop.
Along the outer coasts of Mecklenburg-Vorpommern, the typical winter minimum was observed in January and February, but with some clearly elevated values. For example, in the Pomeranian Bight, the measured chlorophyll-a levels in some cases were 600 % above the long-term monthly mean. A "monoculture" of the cryptoflagellate Teleaulax acuta, with 7 million cells/litre, was observed.
Similarly interesting observations were made in the inner coastal waters, where a monoculture of cryptoflagellates occurred in February. Chlorophyll-a levels in the Greifswalder Bodden exceeded the average values by up to 650 %, in the Stettiner Haff by up to 60 %.
This year's spring algal bloom generally showed a stronger and earlier development than in the two preceding years.
In mid-March, a strong bloom of the diatom genus Chaetoceros set in at the station "Seebrücke Kühlungsborn" and lasted until early April. Apart from dinoflagellates (Gymnodinium spp.), the phototropic ciliate Myrionecta rubra prevailed. The naked form of the dinoflagellate Dictyocha speculum occurred from
In the Mecklenburg Bight, an intensive diatom development was observed in March, which consisted mainly of Chaetoceros species (4.0 mm³/L), Thalassiosira nordenskjöldii (1.2 mm³/L), and Thalassionema nitzschioides (0.1 mm³/L). In the outer coastal waters in the east, chlorophyll-a concentrations continued to be far above the long-term monthly means.
In mid-March, a mass development of Skeletonema costatum was observed in the Greifswalder Bodden area. The biomass production in the Stettiner Haff was unusually strong for this month, representing new extreme values in the long-term series for March. Cryptoflagellates like Teleaulax acuta and Plagioselmis prolonga, with an abundance of 97 million cells/litre and a biovolume of 25 mm³/L, were observed in this area.
This development continued also in April when chlorophyll-a values, at concentrations between 102 and 189 mg/m³, continued to be far above the long-term monthly mean (80.0 mg/m³). Besides the above-mentioned cryptoflagellates (16.5 mm³/L), also diatoms became increasingly dominant, as expected.