In spite of permanent frost at the beginning and end of January, this month's mean temperatures between 0.7 °C and 2.5 °C were on the order of the long-term means. Strong precipitation with major snowfalls in many areas at the beginning and end of the month brought 140 – 210 % of the long-term mean. At 20 – 40 hours of sunshine, only 40 – 80 % of the average duration was reached.
Monthly mean temperatures in February, at 3 – 4 °C, were 2 – 2.5 K above the long-term mean; there were no days with ice. Precipitation, at 70 – 100 mm, was about twice the normal amount. Due to a sunny second half of the month with 75 – 100 hours of sunshine, 100 – 140 % of the long-term mean was reached.
March, too, was 1 – 1.5 K too mild, at mean temperatures from 3.9 – 5.3 °C. This month's 2 – 10 frost days were on the order of the mean values of the 1961 – 1990 period. Precipitation levels of 25 – 35 mm brought a deficit of 30 – 50 %. The average duration of sunshine, at 125 – 145 hours, was exceeded by 10 – 20 %.
Mild weather in April brought monthly mean temperatures between 8 and 10 °C, which was 2 – 3 K above normal. Owing to a spell of dry weather with 20 – 30 mm precipitation, only 40 – 60 % of the monthly means was reached. The duration of sunshine, at 180 – 205 hours, was up to 20 % above the monthly means.
Although some periods in May were relatively cool, the long-term monthly means were exceeded by 0.4 – 0.7 K. At only 10 - 35 mm rainfall, less than half the monthly mean values were reached. Also the duration of sunshine, at 175 – 220 hours, was 10 – 20 %
The monthly mean temperatures of 14 – 15 °C recorded in June were on the order of the long-term means, or 0.7 K below it, although the month was mostly too cold. 70 – 120 mm rain fell in the course of the month, locally exceeding the monthly means by up to 80 %. As in the preceding month, the duration of sunshine, at 170 – 220 hours, was 10 – 20 % below average.
The monthly sea surface temperature (SST) mean values were compared to the so-called climatological value (1971 – 1993); their ranking among the highest SST monthly means since 1971 is given in brackets:
In January, the mean temperature of 7.4 °C was 0.8 K above the climatological value (6th)
In February, the mean temperature of 6.6 °C was 0.9 K above the climatological value (7th)
The mean temperature in March was 6.4 °C, or 0.6 K above the climatological value (9th)
The mean temperature of 7.4 °C in April was 0.8 K above the climatological value (6th)
The mean temperature in May, at 9.7 °C, was 0.6 K above the climatological value (10th)
In June, the mean temperature of 12.5 °C was 0.5 K above the climatological value (9th).
The ice winter of 2003/2004 on the German North Sea coast was classified as very weak. The coasts of East Friesland and the North Sea tributaries were completely free of ice, and in the coastal waters of North Friesland only thin, insignificant ice formation occurred in small harbours on three days.
During the annual monitoring of nutrients performed in January/February, the water in the German Bight was generally found well-mixed. Stratification occurred only in the estuaries of the rivers Elbe and Weser.
A strong inflow of Atlantic water into the German Bight led to elevated salinity levels and, consequently, lower nutrient concentrations. At the same time, compression of the Elbe outflow led to higher nutrient concentrations in a narrow stretch off the coast.
In the near-shore area (salinity 30), the following concentrations were measured in January/February 2004:
Phosphate: 1.15 ±0.14 µmol/L; NOx: 31 ±7 µmol/L; silicate: 23 ±3 µmol/L.
Levels in the German Bight, with a salinity of 33, were as follows:
Phosphate: 0.69 ± 0.14 µmol/L; NOx: 17 ±7 µmol/L; silicate: 10 ±3 µmol/L.
The phosphate and silicate values measured in this area no longer differed from the 1936 levels.
Coast of Lower Saxony
In the first six months of 2004, sampling for the determination of bloom forming or toxic algae was not performed along the coasts of Lower Saxony.
The abundance of phytoplankton was low until early April but markedly higher by the end of April.
The dominant species were diatoms of the genus Thalassiosira, but also Thalassionema, Asterionella glacialis, and Skeletonema costatum were observed. Phaeocystis colonies occurred sporadically at first, but became very abundant in May. The dominant diatom species in May was Guinardia delicatula. Also Chaetoceros socialis and Odontella sinensis became more abundant. By early June, phytoplankton stocks had dropped to a low level while zooplankton was abundant and species-rich. Decayed Phaeocystis colonies formed lines of froth on the sea surface. Diatoms had decreased clearly. Noctiluca became more abundant, and high cell concentrations of the ciliate genera Strombidium and Myrionecta were found. After phytoplankton had increased until the middle of the month, stocks declined until the end of June, with water temperatures 3 °C lower than in the preceding year. Among ciliates, Myrionecta rubra was dominant, and among flagellates Noctiluca was slightly more abundant. Zooplankton continued to be abundant and species-rich, with a conspicuously high abundance of Alaurina composita of the Turbellaria order.
North Sylt Wadden Sea
During the weekly plankton monitoring in the Wadden Sea north of Sylt, not only temperature and salinity but also dissolved and particulate nutrients are analysed.
Water temperatures in January and February ranged between 0 and 4 °C, and increased continuously from March until reaching their maximum of 21 °C in August. The salinity minimum of 26 was measured in February, rising to 31 by August.
The phytoplankton spring bloom was rather small and reached its maximum in mid-April, dominated by the diatom Odontella aurita. Chlorophyll levels reached only 17 µg/L, compared to 48 µg/L in the preceding year.
The following, rather intensive, Phaeocystis bloom reached its maximum Chl-a level of 25 µg/L on 20 May. In the course of summer, the phytoplankton biomass decreased to about 3 µg/L, with only a minor phytoplankton bloom of up to 7 µg/L Chl-a observed in early July. Phaeocystis was observed regularly until mid-July. In early July, the diatom Rhizosolenia imbricata, and at the end of July Guinardia striata were observed frequently.
Potentially toxic algae (Alexandrium, Dinophysis, Chattonella) were observed several times, but only at low cell concentrations.
Schleswig-Holstein coastal waters
As a typical seasonal phenomenon of early June, the foam producing alga Phaeocystis globosa was very abundant along the entire west coast of Schleswig-Holstein, but with a clearly larger number of colonies than last year. The algal colonies in most areas decayed in mid-June. Diatoms occurred in small to medium numbers.
Until the end of June, the species spectrum of phytoplankton was much too small for the season, with markedly lower numbers than usual, which was due to the fact that air and water temperatures had been too low for weeks. The dominant diatom species were Rhizosolenia imbricata, Guinardia delicatula, and G. flaccida. Dinoflagellates like the luminescent Noctiluca scintillans occurred only sporadically. Phaeocystis colonies had virtually disappeared.
Surveys of fish stocks in the German Bight at the beginning of the year confirmed a steady increase in herring catches over the past four years, but average cod catches were still extremely low. Also surveys of young fish stocks in the North Sea showed that total catches of most commercially exploited fish species were on the order of the preceding years' minimum levels, without any lasting improvement in the stock situation being likely in the foreseeable future. The 2003 cod year class was confirmed to be extremely weak.
Surveys of the frequency and distribution of malformations in pelagic fish embryos found low malformation rates in all species surveyed. Considering the disparity in the Member States' control and enforcement systems which hinders equal implementation, the European Commission had proposed the establishment of a Community Fisheries Control Agency for better implementation of the rules of the reformed Common Fisheries Policy (CFP).
In contrast to weather conditions in the North Sea region, monthly mean temperatures in the Baltic in January were up to 1 K too cold, at 0.2 – 2.1 °C. The number of ice days (8 – 15) and frost days (19 – 24) exceeded the long-term means by up to four days. Rainfalls, at 50 – 90 mm, were 20 – 65 % above the monthly mean. The snow cover was thin in most areas. The duration of sunshine in the western Baltic region, at some 20 hours, was only about 50 % of normal, whereas the 50 – 55 hours of sunshine east of Rügen were above average, reaching up to 144 %.
In February, the mean temperatures from 1.8 to 3 °C were about 2 K above the long-term mean. The number of frost days, at 10 – 17, was below average. 30 – 70 mm rain was recorded, corresponding to 115 – 245 % of the long-term mean. At 70 – 90 hours of sunshine, the long-term mean was exceeded by 20 %. Values 10 – 20 % below average were only recorded east of Rügen.
March, at mean temperatures of 4 – 5 °C, was 1 - 2 K too warm and too dry. Precipitation, at only 20 – 40 mm, was 20 – 40 % below the mean values. 120 – 130 hours of sunshine were recorded, exceeding the long-term means by 10 – 20 %.
In the mild month of April, monthly mean temperatures ranged between 6.8 and 9 °C, which was 1.8 – 2.8 K above the 1961 – 1990 reference values. Rainfall, at 25 – 40 mm, was about 70 – 90 % of normal and was slightly higher than in the North Sea region. The duration of sunshine was 200 – 250 hours, which was 10 – 35 % above normal.
In May, with monthly means between 10.3 and 12.2 °C, the long-term means were exceeded by nearly 1 K. Precipitation ranged between 30 and 45 mm (locally up to 65 mm), which was locally above or below the long-term means. The duration of sunshine, at 200 – 230 hours, was 20 % below average, with the exception of the islands.
June 2004 was too cold and too wet, with too little sunshine. The monthly mean temperatures, at 14 – 15 °C, were 1 K below the reference values. This month, 50 – 80 mm precipitation was recorded, which was up to 50 % above normal. At 180 to nearly 230 hours of sunshine, the duration of sunshine was some 15 – 25 % below the mean values.
In January, water temperatures on the Baltic coasts of Schleswig-Holstein and Mecklenburg-Vorpommern, at 2.2 °C, corresponded to the values of the reference series. In February, 1.2 °C and 1.5 °C were reached, respectively, which was below the average of the reference series. Also in March, mean water temperatures were below average, at 2.3 and 2.6 °C, respectively. Average temperatures of 5.9 and 5.4, respectively, were recorded in April. The mean temperatures in May, at 11.8 °C, and June, at 15.7 °C, also corresponded to the reference series
(1997/98 to 2004).
The monthly mean water levels on the Baltic coasts of Schleswig-Holstein and Mecklenburg-Vorpommern in January corresponded to the time series (1991 – 2000 and 1993 – 2002, respectively). The highest water level was recorded in Eckernförde on 2 January 2004, at 94 cm above normal, and the lowest level in Wismar on 31 January, at 84 cm below normal.
The monthly means in February were above the reference series in Kiel, Travemünde, and Warnemünde, and below it in Koserow. Nevertheless, the highest value of 573 cm was measured in Koserow on 18 February, and the lowest value of 443 cm in Eckernförde on 24 February.
In March, water levels in Schleswig-Holstein on average matched those of the reference series, while in Mecklenburg-Vorpommern they were below it. However, the highest value of 575 cm was measured in Wismar on 3 March, and the lowest one, at 363 cm, in Schleswig on 21 March.
The monthly means in April were slightly above the reference series in Schleswig-Holstein, and slightly below it in Mecklenburg-Vorpommern.
In May, the monthly mean values were 5 – 11 cm above the reference series. The lowest water level was measured in Flensburg on 14 May, at 448 cm. Wismar recorded the highest level of 559 cm on 23 May.
Also in June, the monthly mean values were 3 – 6 cm above the reference series. The highest water level was recorded in Wismar on 9 June, at 550 cm, and the lowest level in Flensburg on 14 June, at 437 cm.
Compared to the respective mean discharges in the reference period from 1941 to 2000, the surface runoff volumes in the Odra area (gauge station Hohensaaten-Finow) in the period from January to June were markedly lower in some cases.
In the first week of January, ice conditions in the northern Baltic lagged about 2 1/2 weeks behind average despite the marked increase in ice mass. In the southern Baltic, stronger frost led to local ice formation in the protected inner fairways of Mecklenburg-Vorpommern and the Baltic States, which continued until the end of the month. In the northern Baltic, this winter's first maximum of ice formation was reached, with an average ice extent.
In early February, thawing temperatures in the southern Baltic caused the ice in the inner fairways to melt. Strong frosts in the northern Baltic region led to another increase in ice thickness and ice extent.
In mid-March, this season's maximum of ice formation was reached when the Gulfs of Finland and Riga and the northern Gulf of Bothnia were completely covered with ice, with wide belts of drift ice along the coastline of the Bay of Bothnia, and a narrow belt of new ice along the coasts of the northern Baltic. Until the end of the month, variable frost situations and occasionally strong winds caused intensive ice drifts in these areas.
At the beginning of April, ice ridging still occurred in wide areas of the Bay of Bothnia. In the course of the month, the drift ice decreased, and fast ice along the coastline became brittle. By early May, a marked decline of ice had set in which, due to a temperature increase and rainfalls, reached also the northern part of the Bay of Bothnia by the end of May.
The ice season of 2003/2004 was shorter than usual, with the maximum ice extent in the Baltic corresponding to that of a moderate ice winter (about 155,000 km²). On the German Baltic Sea coast, this ice season was classified as a weak ice winter.
In the outer coastal waters of Mecklenburg-Vorpommern, areally averaged winter concentrations (January, February) of phosphate and nitrate were 50 % below the long-term mean. By the end of March, both nutrients were hardly detectable, with the exception of the Pomeranian Bight. In April and May, the levels remained very low, and also in June the situation was unchanged, except in the western part of the Mecklenburg and Pomeranian Bights, where the nitrate levels still were relatively high (3 – 4 µmol N/L).
Also in the inner coastal waters of Mecklenburg-Vorpommern, the phosphate concentrations in January and February on average reached only 40 % of the long-term mean, and also the nitrate values were clearly below the long-term mean. Phosphate levels continued to decrease in March, while nitrate levels remained unchanged. In April/May, concentrations of both nutrients were very low, and locally below the detection limit. While phosphate levels increased again slightly from May to July, nitrate was depleted in most areas in June; an exception was the "Kleines Haff" (at 9.81 µmol N/L).
In the outer coastal waters of Mecklenburg-Vorpommern, oxygen concentrations in the surface water were very good until June, also in the bottom water. Minor regional deficits were first observed in June, marking the beginning of a slight oxygen decrease in the western Mecklenburg Bight, which intensified in July, at values from 4 to 6 mg O2/L.
In the inner coastal waters of Mecklenburg-Vorpommern, oxygen levels in the surface and bottom water were good. In June, elevated saturation values were found in the surface water of the Unterwarnow and Kleiner Jasmunder Bodden.
Surveys in the area from the Kiel Bight to the northern Gotland Basin in February showed anoxic conditions with hydrogen sulphide formation only in the western Gotland Basin, at more than 90 m depth.
By March, the oxygen situation in the bottom water of Landsort Deep had improved following the major inflow of cold water in January 2003. The bottom water was free of H2S, which was only found in an intermediate layer at about 150 m depth. Karlsö Deep still had not returned to oxic conditions. The situation was largely unchanged in April/May.
Baltic coast of Schleswig-Holstein
At the beginning of monitoring in early June, an algal bloom of the naked stage of Dictyocha speculum was observed, with up to 9 million cells/liter. However, at the end of June/beginning of July, the development of the summer assemblage of plankton was still slow. Cool and windy weather delayed the normal succession of microalgal communities by several weeks. Small flagellate species with high cell concentrations were dominant, and medium to high cell concentrations of typical summer diatoms were observed only in a few areas. Dinoflagellates continued to be rare.
Monitoring station "Seebrücke Heiligendamm"
In January and February, the abundance of phytoplankton was low. During a short period in mid-February, a mass development of Teleaulax spp. (Cryptophyceae) and Heterocapsa rotundata (Dinophyceae) occurred. The maximum of the spring bloom was reached in the 11th week (9.03), with a (temporarily strong) dominance of Thalassiosira nordenskioeldii (biomass of 1473 mg/m³) and much smaller biomasses of Skeletonema costatum, Chaetoceros cf. debilis and Prosira glacialis. The bloom ended on 23.3.2004. In 2003, the bloom occurred earlier and was dominated by Skeletonema costatum. In 2004, the biomass of the photoautotrophic ciliate Mesodinium rubrum remained low, as in the preceding year.
In early April, the naked stage of the Chrysophycea Dictyocha speculum (429 mg/m³) developed and remained the dominant or sub-dominant species until the end of June. From 2.6, the large diatom Dactyliosolen fragilissimus developed very strongly (2757 mg/m³ on 22.6.) for about one month, followed by Cerataulina pelagica (316 mg/m³) from 20.7. to 3.8..
In early August, the typical seasonal cyanobacteria species Nodularia spumigena, Aphanizomenon sp., and Anabaena spp. developed but did not form blooms as in the preceding year.
Outer coastal waters of Mecklenburg-Vorpommern
January and February were without any special developments regarding the species spectrum of phytoplankton and concentrations of chlorophyll-a. Chl a values ranged between 0.6 µg/L (north of Warnemünde) and 4.6 µg/L in the Bay of Lübeck, where the onset of the springtime algal development was slow, starting with the diatom species Skeletonema costatum, Thalassionema nitzschioides, and species of the genera Thalassiosira, Melosira, and Chaetoceros. The total biovolumes in this area varied between 0.2 and 0.6 mm³/L, and remained below 0.1 mm³/L in many other areas. The cryptoflagellate Teleaulax acuta occurred along the entire outer coast.
In March, Chl a concentrations dropped from 1.6 – 6.5 µg/L at the beginning of the month to 1.0 – 1.7 µg/L at the end of the month, marking the end of the spring algal bloom in the western Baltic areas. In the eastern Baltic areas, peak chlorophyll-a levels were measured between Greifswalder Oie and the inner Pomeranian Bight at the end of March, where the measured value of 22.8 µg/L clearly exceeded the long-term means; Teleaulax acuta and diatoms of the genus Melosira dominated in this area.
In May, the chlorophyll-a levels ranged between 1.2 µg/L off Fischland and 7.0 µg/L east of Sassnitz, corresponding to 280 % of the long-term means. Farther east, values below the long-term means were measured, and slightly elevated values in the sea area extending north of Boltenhagen to the waters northwest of Hiddensee. The end of the spring algal growth was marked by biomass volumes ranging from 0.5 mm³/L north of Boltenhagen to 1.0 mm³/L in the Pomeranian Bight, where Diatoma elongatum was dominant; the dominant species between Boltenhagen and Warnemünde was Dictyocha speculum.
In June, chlorophyll-a concentrations varied between 1.1 µg/L northwest of Hiddensee and 4.7 µg/L in the Pomeranian Bight, with monthly mean values clearly exceeded between Boltenhagen and Fischland. Phytoplankton biovolumes ranged between 0.1 mm³/L northwest of Hiddensee and 1.1 mm³/L north of Boltenhagen.
Inner coastal waters of Mecklenburg-Vorpommern
In January and February, chlorophyll-a levels varied between 0.9 µg/L and 90.9 µg/L, which was normal for the season. Biovolumes mostly were below 0.1 mm³/L but reached 0.5 mm³/L in the brackish "Salzhaff" and Strelasund.
In March, Chl a values between 1.7 (Salzhaff) and 135 µg/L (Darss coastal lagoons) were measured. The values in some areas were markedly below the long-term means, while at some stations they were far above them. In the Greifswalder Bodden, for example, the Chl a values were 4 - 6 times higher than normal, which was due in part to massive growth of the diatoms Skeletonema costatum and Melosira arctica. In the waters of Stettiner Haff, diatoms of the genus Thalassiosira as well as Teleaulax acuta led to elevated Chl a values. By 24.3., chlorophyll-a levels and biovolumes had dropped sharply.
In the sea area of Strelasund/Greifswalder Bodden, strikingly low chlorophyll-a values between 3.0 and 7.4 µg/L were measured in April (the long-term means range from 16.5 to 20.0 µg/L). On the whole, the diversity of the phytoplankton community was low, and the transition
to the summer assemblage was dominated by Chrysophyceae. Small quantities of Heterocapsa rotundata and Teleaulax acuta were present in all areas.
The chlorophyll-a concentrations in May ranged between 2.4 µg/L in the Wismar Bight and 207 µg/L in the Unterwarnow and were mostly below the long-term means. However, the extreme value in the Unterwarnow was 4 time higher than normal, reflecting the dominance of the diatoms Stephanodiscus hantzschii and Melosira granulata. Phytoplankton in the inner coastal waters of the western Baltic was dominated by Dictyocha speculum and Skeletonema costatum. In the Greifswalder Bodden/Strelasund area, extremely high pico- and nanophytoplankton levels were found. In the waters of Stettiner Haff, an atypical phytoplankton community of small flagellates (130 million cells/litre, biovolume 4.3 mm³/L) and diatoms of the genus Coscinodiscus was found, the latter part of the summer assemblage. First Cyanophyceae of the genus Microcystis as well as Aphanizomenon flos-aquae were observed.
Also in June, the Chl a values were mostly below the long-term means. Values ranged from 1.5 µg/L in the brackish "Salzhaff" to 107 µg/L in the Stettiner Haff, with long-term means clearly exceeded; this was partly due to the typical early summer growth of the diatom species Coscinodiscus (biovolumes of 7.0 mm³/L at 237,000 cells/litre).
Cod average catches per hour in the Mecklenburg Bight and Arkona Sea were at the prior-year level, with an above-average proportion of the 2003 year class in the total cod stock. In the Bornholm Sea, cod catches again had declined markedly. The abundance of sprat in the Bornholm Basin in 2004 returned to the levels of 1999 to 2002, after a strong decline had been observed in 2003 due to the major inflow of cold water. A higher proportion of herring was found in the catches of the area investigated, i.e. Arkona Sea, Bornholm Sea, and western Gotland Sea.