October 2001 was the warmest October on record since the beginning of regular temperature measurements toward the end of the 19th century. Precipitation was clearly below average.
At monthly mean temperatures between 7 and 9 °C, November was relatively warm. Rainfalls showed a decreasing tendency toward the east.
In December, the duration of sunshine and rainfalls were above average. While mean temperatures at the coasts and on the North Frisian islands, at 2 °C, were below the long-term mean, temperatures in the German Bight and on the East Frisian islands, at 4.5 °C, exceeded the long-term mean. Also the freezing temperatures clearly reflected this difference.
The October and November values reached 13.2 °C and 11 °C, respectively. At 1.3 K above the climatological value, they ranked first in comparison with the past years (since 1971). The sea surface temperature (monthly mean) of 8.7 °C in December was 0.8 K above the climatological value.
In the Wadden Sea of Lower Saxony, critical cell concentrations of potentially toxic species (Dinophysis acuminata,
Chrysochromulina) were not observed.
Colonies of the foam-forming Phaeocystis alga occurred only sporadically in October. The abundance of the bioluminescent Noctiluca scintillans was generally low at all stations along the East Frisian coast. Diatoms of the Pseudo-nitzschia group and the ciliate Myrionecta rubra were not found at any of the stations at the end of October.
Near Helgoland, phytoplankton stocks were low. Potentially toxic Dinophysis acuminata were only abundant in early October. The diatom species Melosira sulcata and Odontella sinensis were observed as well as single Rhizosolenia robusta cells. Among flagellates, primarily small cells were found; Ceratia were hardly observed any more.
Nauplius continued to be relatively abundant until late October.
In the North Sylt Wadden Sea, phytoplankton showed the typical seasonal development of autumn; no exceptional blooms were observed. The species spectrum of diatoms was much larger than in summer, which is typical of the season. It was large in comparison with the preceding years. Chaetoceraceae showed the highest species diversity, which is normal for the season. The most abundant dinoflagellates were Noctiluca scintillans and Prorocentrum micans (potentially toxic).
An inventory of groundfish stocks in the German Bight showed a good 2001 year class of whiting and cod. However, cod over two years old were rarely caught. Catches of dab were of average size, those of plaice above average, especially farther from the coast. Good saithe catches as compared to the preceding years indicated a recovery of saithe stocks.
Also in 2001, seal populations in the Wadden Sea continued to increase, continuing the positive trend since the virus epidemic of 1989.
October was unusually mild (mean temperature: 12 - 13 °C), setting new temperature records. It was the warmest October since the beginning of regular temperature measurements toward the end of the 19th century. Precipitation was low (20 - 30 mm).
Also November, at mean temperatures around 4 - 7 °C, was relatively mild, dry, and quite sunny in some areas (coast of Schleswig-Holstein).
At monthly mean temperatures between 0.1 °C and 2.1 °C, December was too cold, with average rainfall. Some heavy snowfalls in the last third of the month led to a complete snow cover. There were few hours of sunshine.
In late October/early November, sea surface temperatures ranged between 8.4 °C (Landsort Deep) and 12.9 °C (Kiel Bight), which was up to 2.5 K above the long-term means (1971 - 1990). Also the bottom water temperatures were higher than average (1971 - 1990).
An evaluation of measurements made during the monitoring cruises of RV Humboldt (IOW, Baltic Sea Research Institute) shows a continuous, slow temperature and salinity decrease since the last major inflow of highly saline water in 1997/98.
Near the bottom, salinities continued to decrease slowly also during the autumn months, indicating a continuing stagnation.
Water levels in October (450 cm - 550 cm) were 1 - 6 cm below the reference series. Three storm surges occurred in November, with water levels each time rising more than 1 metre above generalized mean sea level. The monthly mean values (511 - 534 mm) were up to 30 cm above the values of the reference series.
On 20 December, a moderate storm surge occurred which was followed by a negative surge. The monthly mean values (508 - 544 mm) were 9 - 14 cm above the values of the reference series.
On 6 November, about one week earlier than the average date, the first ice formation of this winter occurred on the north coast of Bottenvik at air temperatures around minus 10 °C. Shipping was not yet affected. At the beginning of the 47th week, in the easternmost part of the Gulf of Finland, ice formation in the approaches to St. Petersburg and Vyburg started "on schedule".
In the first half of December, there were only short spells of severe frost in the northern Baltic. The ice increase was slow in most areas, and consisted mostly of an increase in ice thickness on the north coast of Bottenvik and in the bays of the easternmost part of the Gulf of Finland.
In the 51st week, upper level cold air flowed into the northern Baltic region from the north. Severe to very severe permanent frost led to strong ice formation in almost all areas along the coast of the Gulfs of Bothnia and Finland.
The phytoplankton biomass at the monitoring station Seebrücke Heiligendamm was very low, and was composed mainly of Ceratium tripos, Mesodinium rubrum, Hemiselmis sp., Proboscia alata, and Coscinodiscus granii. In November, weak growth of Ceratium species and of the diatom Guinardia flaccida was observed. By December, biomasses had reached their low winter level.
A survey of fish stocks in the western Baltic confirmed the currently very poor condition of market size cod stocks. The last strong year-class 1997 has been completely harvested. Turbot catches showed a decreasing trend in comparison with the past three years, while plaice surprisingly showed an upward trend. The dominant proportion of older sprat (> 10 cm) observed in 2000 was not confirmed in 2001.
First results of a survey of the flounder year-class 1999 in the area of the Odra Bank also indicated a very weak year-class. A similar trend is observed for turbot in the Odra Bank area and dab in the Mecklenburg Bight.