MURSYS - North Sea and Baltic Sea - Report 1 2003





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MURSYS - North Sea and Baltic Sea - Report 1 2003

   
 
 

Marine Environmental Reporting System - Abstract - Reporting Period: 1 January - 30 June 2003

 

North Sea

Weather

The monthly mean temperatures in January were 1 - 2 °C. Precipitation levels ranged between 50 and 70 mm. 30 to 35 hours of sunshine were recorded.
In February, monthly mean temperatures of 0.8 to -1.0 °C were recorded. Precipitation, at 13 - 22 mm, was 40 - 70 % below the mean values. The sun shone 100 to 125 hours.
Also March was too dry and warm, with an above-average duration of sunshine. The monthly mean temperatures were 4 - 6 °C. Precipitation was low, at 15 - 33 mm, and the duration of sunshine was 160 to 172 hours.
April was also too mild. The monthly mean temperatures ranged between 7.6 and 9.6 °C. Abundant rainfalls of 20 - 30 mm increased the amounts of precipitation in large areas to 40 - 50 mm, locally more than 60 mm. The 217 to 242 recorded hours of sunshine exceeded the long-term means by 30 to 40 %.
May, too, was slightly too warm, at mean temperatures of 11 - 12 °C, although the coastal region of North Germany did not come under anticyclonic influence until the end of the month, when summer temperatures rose to 25 °C. The cyclonic influence at the beginning of the month accounted for rainfalls of 52 - 118 mm, which exceeded the mean values by 25 - 120 %. The recorded 205 to 256 hours of sunshine corresponded to the average values.
June 2003 was the warmest June on record in the Federal Republic of Germany since 1901. Also the mean temperatures on the North Sea coast, at 16 - 18 °C, were too high by about 2 - 3 K, and the 5 - 7 summer days were also above average. Rainfalls, at 30 - 60 mm, were up to 40 % below the long-term means. At 240 to 280 hours of sunshine, the mean values were exceeded by 10 - 20 %.

Water temperatures

The water temperature in January was 6.8 °C and exceeded the reference value by 0.3 K. The surface water temperature in February was 6.1 °C, which was 0.4 K above the reference values. The water temperature in March was 6.2 °C, or 0.5 K above the reference values. The water temperature of 7.4  °C in April was 0.7 K above the reference values. The mean temperature of the surface water in May was 9.9 °C, or 0.9 K, above the reference values. In June, the reference values were exceeded by 1.7 K, at a mean water temperature of 13.7 °C.

Ice conditions

In the North Frisian Wadden Sea waters, local new ice or thin ice formed in January. Open to close ice and locally compact ice drifted in the area of the tidal flats. The harbour of Tönning was closed. Open ice occurred locally in the North Sea tributaries and Kiel Canal. Rather compact, 10 - 30 cm thick ice formed in the harbour of Hamburg. The situation changed in the third calendar week. Due to thawing temperatures, the North Sea was ice-free. In mid-February, thin drift ice occurred in large areas of the North Frisian coastal waters, and the formation of new ice was observed. At the end of February, some remaining ice was still observed locally along the North Frisian coast.

Nutrients

The annual trend monitoring for nutrients and heavy metals from the end of January to early February showed that nutrient levels both in the nearshore waters and German Bight were within the fluctuation range of the preceding years. Phosphate concentrations of 0.90 µmol/L ±0.17 µmol/L were measured in the nearshore waters, and 0.56 ±0.17 µmol/L in the German Bight. The silicate concentration in the nearshore waters was 27 ±4 µmol/L, and in the German Bight 11 ±4 µmol/L. The phosphate and silicate values did not differ significantly from those of the year 1936. Fixed nitrogen (nitrate + nitrite + ammonium) in the nearshore waters reached values of 48 ±10 µmol/L, and in the German Bight about 18 ±5 µmol/L.
The preceding year's flood events in the Elbe river in summer and autumn did not have any detectable effects in the German Bight.

Phytoplankton

Coastal waters of Lower Saxony
After a strong winter with ice coverage followed by a long and cold spring phase, cell numbers of the bioluminescent alga Noctiluca rose to unexpectedly high levels of 1139 cells/litre by 5 May near Norderney, at a water temperature of 12.9 °C; until mid-April, water temperatures had still been below 10 °C. On 9 May, seasparkle was observed during very calm weather. The first "red tides" were reported from the German Bight. At the same time, the abundance of Noctiluca near Norderney dropped steeply to 40 cells/litre.
The mucilage and foam producing spherical alga Phaeocystis had also exceeded its spring maximum by that time. On 22 April, colony numbers were about 107 per litre, which was far below the bloom level, and continued to decrease. Phaeocystis was almost non-existent.

Helgoland Roads
Phytoplankton growth began at about the same time as in 2002, in early April. The dominant species initially was Thalassiosira punctigera, later also Odontella aurita and, in mid-April, Thalassiosira nordenskioeldii. By late April, the cell concentrations and carbon values of phytoplankton had decreased again. The abundance of small flagellates was at about the same level as in March and April of the preceding year. Dinophysis acuminata was slightly more abundant in April 2003 than in 2002. In early to mid-May, the abundance of phytoplankton was low. In mid-May, many copepods, even phyllopods, larvae of many benthic organisms and pelagic fish eggs were found in plankton. Small and larger ciliates were surprisingly abundant, especially Myrionecta rubra toward the end of the month. Among diatoms, Cerataulina pelagica and Rhizosolenia shrubsolei had become more abundant. In June, phytoplankton continued to increase. The dominant diatoms initially were Nitzschia seriata s.l. and Cerataulina pelagica, followed by Rhizosolenia shrubsolei toward the end of the month. Flagellates became more abundant in the course of June, especially Noctiluca assemblages. Ceratium fusus was replaced by Ceratium longipes at the end of the month. Among ciliates, the abundance of Myrionecta rubra decreased markedly.

North Sylt Wadden Sea
The species diversity of phytoplankton was determined weekly. The method used was to enrich the phytoplankton from several cubic metres of water using plankton nets (20 and 80 µm). The unpreserved, living plankton was determined immediately by means of an immersion microscope.
This year's winter was the coldest winter since 1996. The mean water temperature between January and March was about 0.8 °C. Between late February and mid-April, temperatures rose from -0.6 °C to 5 - 6 °C. Salinity was about 28. The maximum nutrient levels of this winter were: Si: 25 - 35 µM; PO4: 1.2 µM; NO3: 50 µM; NO2: 1.2 µM; NO4: 10 µM.
In keeping with the low winter temperatures, this year's spring algal bloom was intensive and relatively early. On 20 March, a maximum chlorophyll concentration of about 50 µg/L was observed. In comparison: the year before (2002) was rather warm (3.4 °C), and the bloom was about 14 days later with maximum levels of some 28 µg chla/L.
Nutrient consumption by the algae during the bloom led to a strong decrease in concentrations. Si, PO4 and NH4 reached values of 0.2, 0.05, and 0.3 µM respectively. Data on NO3 and NO2 is not yet available.
The species spectrum was dominated by diatoms, as every winter. The number of species was about 40. The number of dinoflagellate species was 3 or 4, rising to 8 by April. Before and during the bloom, Odontella aurita and Porosira glacialis were the dominant species. During and after the spring bloom, also Skeletonema costatum was very frequent. Odontella and Thalassiosira were the diatom group with the highest species diversity in the last months.

Coastal waters of Schleswig-Holstein
At the end of May, the diversity of phytoplankton summer species in the coastal waters was low, with clearly different distributions. Diatoms prevailed, with increased cell concentrations west of Sylt. In June, with diatoms still dominant, the species spectrum of dinoflagellates increased. The bioluminescent Noctiluca scintillans and foam-forming alga Phaeocystis globosa were frequent until mid-June but declined toward the end of the month.

Baltic Sea

Weather

The mean temperature in January was about 0 - 1 °C. Precipitation was 25 - 40 mm, and the duration of sunshine was only 20 - 30 hours. February was too cold, much too dry, and unusually sunny. The monthly mean temperatures were about -1 °C. Precipitation was 3 - 9 mm, and 88 to 114 sunshine hours were recorded. Average temperatures in March ranged between 2.8 and 4.3 °C, with 9 - 18 mm precipitation. The sun shone on 160 to 205 hours.
April was too mild and mostly too dry, with an above-average duration of sunshine. The monthly mean temperatures ranged between 5.6 and 8.1 °C. Monthly precipitation was between 30 and 50 mm. At 230 to 255 hours of sunshine, the long-term mean was exceeded by 30 - 40 %. At mean temperatures between 12 and 14 °C, May was also too warm. Rainfalls differed considerably, ranging between 33 mm and 80 mm. At 250 - 291 hours of sunshine, the reference values were exceeded by up to 12 %. The highest June temperatures since 1901 were recorded in 2003. Also along the western and southern Baltic, temperatures were 2 - 3 K above normal, at 16 - 18 °C. The number of summer days, at 1 - 8, was twice as high as usual. Precipitation, at 30 - 50 mm, was up to 40 % below the mean values. 250 to 300 hours of sunshine were recorded, which was about 10 % above the reference values.

Water temperatures

Water temperatures in January, at 0.7 °C, were about 1 K below the reference values. In February, water temperatures of 0.4 °C were recorded, which was 1 K below the reference values. Water temperatures in March ranged between 1.8 and 2.4 °C on average. Water temperatures in April ranged between 4.8 and 5.5 °C on average. In May, the mean water temperature of 11 °C corresponded to the reference values. The mean water temperatures in June, at 15.8 to 16.9 °C, were about 1 K above the values of the reference series.

Water levels

The lowest water level in January, 402 cm, was recorded in Flensburg on 12 January. The highest flood level, recorded in Wismar, was 622 cm. The lowest water level in February was 438 cm, measured in Wismar on 3 February. In Warnemünde and Wismar, max. 34 cm above normal was recorded on 5 February. The monthly mean values were 18 cmbelow the reference values. In March, the highest water level of 559 cm was measured in Flensburg on 20 March, and the lowest water level of 430 cm in Wismar on 6 March. The mean water levels were 2 - 3 decimeters below normal. The highest April water level was measured on 4 April in Wismar, at 611 cm. The lowest water level was measured on 4 April in Flensburg, at 444 cm. The monthly mean values at all stations exceeded the reference values. In May, the monthly mean water levels were below the reference values at all stations. In June, the lowest water level was measured in Kiel-Holtenau, at 416 cm. The monthly mean values were 5 - 9 cm above the values of the reference series.

Ice situation

An early beginning of the ice season and long periods of strong frost led to an extreme ice cover in early January. As early as the end of the first week of January, the Gulfs of Bothnia, Finland and Riga had an almost complete ice cover.
In mid-February, the formation of new ice continued, with a complete ice cover in the inner harbour of Kiel, thin ice and new ice formation on the river Schlei and in the coastal waters of Mecklenburg-Vorpommern. Complete ice cover in the harbours and inner fairways.
In March, the ice winter ended at the German Baltic Sea coast. On the whole, this year's ice season in the German waters, with ice thicknesses of max. 30 cm, was rather moderate. It lasted about ten weeks and was limited mostly to the inner fairways. In the northern Baltic region, the ice cover decreased slightly, and there were wind-induced changes in the ice situation.
Wind-induced changes in the ice situation occurred also in April. In the northern Baltic, major ice ridging occurred temporarily at sea and along the windward coasts. Rising air temperatures in mid-April led to an accelerated seasonal ice decline. Rainfalls in the southern regions were another factor contributing to ice decay. The last ice in the eastern Gulf of Finland and northern Bay of Bothnia melted in mid to late May. The dates at which the last ice melted ranged among the latest ones observed in the past decades.

Major inflow of highly saline water

From 16 to 25 January, for the first time since 1993, a major inflow of high-salinity, cold North Sea water with an extremely high oxygen content was recorded at Darss Sill and in the Arkona Basin. The cause of this rare and unusual occurrence was the extraordinarily low water level of the Baltic Sea in early January.

Nutrients

In the outer coastal waters of Mecklenburg-Vorpommern, phosphate concentrations from March to June were very low, close to the detection limit almost in the entire sea area, and could not be measured. Also the nitrate levels during this period were very low or close to the detection limit.
The same situation was found in the inner coastal waters of Mecklenburg-Vorpommern, where phosphate levels were very low or below the detection limit from March to June. Also the nitrate levels were very low in March, and were markedly lower than usual especially in the Lower Warnow waters. Slightly higher concentrations were only observed in the inner Wismar Bight. This situation continued in April, with concentrations corresponding to 10 % of the long-term monthly mean (LMM). From May to June, nutrient levels continued to fall, and nitrate was only present in traces or the levels were below the detection limit.

Oxygen

Oxygen levels in the surface water of the outer coastal waters of Mecklenburg-Vorpommern were very good until April/May, with minor local oversaturation. Good oxygen concentrations were found in the bottom water, with a beginning trend toward decreasing levels only apparent in the western Mecklenburg Bight. The oxygen situation in the surface water continued to be very balanced in all areas in June. Between Warnemünde and Ahlbeck, also the bottom water showed good oxygen levels, whereas in the western Mecklenburg Bight, the saturation had dropped to 57 - 72 %.
In all inner coastal waters of Mecklenburg-Vorpommern, oxygen supply in the surface water was very good from March to May, with local oversaturation in some places. Also in June, the oxygen situation of the surface water was very balanced. A minor deficit of 20 - 30 % was only measured in the Salzhaff and southern Lower Warnow in the bottom water, while a slight oversaturation was found in the Wismar Bight.

Phytoplankton

Baltic coast of Schleswig-Holstein
When sampling started in early June, diatoms in the Flensburg and Kiel Fjords had already increased strongly and were forming first algal blooms. In the other areas off Heiligenhafen and in the Bay of Lübeck, relatively little plankton was observed. Filamentous blue-green algae occurred only in the outer Bay of Lübeck. The situation continued largely unchanged until the end of June.

Monitoring station "Seebrücke Heiligendamm"
The phytoplankton biomass was small until mid-February. At the end of February, there was an explosive growth of diatoms, with the Skeletonema costatum bloom continuing until mid-March. This was followed by the development of Cryptophyceae (especially Teleaulax sp.). The usual replacement of diatoms by large, athecate dinoflagellates was very weak in 2003. In late April, mainly Dictyocha speculumand Pseudopedinella sp. were found. A phase of very low phytoplankton biomass dominated by Cryptophyceae (Hemiselmis, Teleaulax, Plagioselmis) continued until the end of May. After a moderate increase in biomass in mid-June, Ceratium tripos for the first time became clearly noticeable. The typical summer bloom of diatoms began in late June, represented by Guinardia flaccida.

Outer coastal waters of Mecklenburg-Vorpommern
In January and February, chlorophyll-a values between 1.2 mg/m³ and 4.8 mg/m³ were measured between Warnemünde and Darßer Ort. Off Warnemünde, concentrations were up to five times higher than the long-term monthly mean (LMM). In the winter months, cryptoflagellates of the genera Plagioselmis and Teleaulax were present, as expected. Besides Skeletonema costatum, unspecified centric diatoms of the genus Thalassiosira continued to be found (0.4 mm³/L).
In March, chlorophyll-a levels in the waters between Boltenhagen and Darßer Ort were far below the LMM levels. However, between NW Hiddensee and E Saßnitz, measured values clearly exceeded the LMM values (3.5 mg/m³). A Skeletonema bloom was observed in this sea area. The biovolumes reached up to 1.8 mm³/L at about 8 million cells per liter, which explains the elevated chlorophyll-a values in this sea area.
In April, chlorophyll-a levels along the entire outer coast generally reached only 30 - 40 % of LMM. An exception was the Pomeranian Bight, where the measured value of 23.1 mg/m³ was 2.5 times higher than LMM. Also the phytoplankton biovolumes were clearly below the long-term monthly means. Besides Heterocapsa rotundata, small Cryptophyceae of the genera Teleaulax and Plagioselmis prevailed. Diatoma elongatum and Achnanthes taeniata occurred in the Pomeranian Bight.
Chlorophyll-a levels in May were, sometimes markedly, below the long-term monthly mean (LMM). In the Pomeranian Bight, just under 20 % of LMM was reached. The biovolumes in May were very low. The highest value, at 0.6 mm³/L, was measured in the Pomeranian Bight, where the dominant genus was Chaetoceros.
In June, chlorophyll-a concentrations in the waters between Boltenhagen and north-west Hiddensee were largely within the range of the long-term means for June, although the value of 6.0 mg/m³ found in the Pomeranian Bight was only 35 % of LMM. The biovolumes were clearly below LMM. Potentially toxic Cyanophyceae such as Nodularia spumigena and Aphanizomenon "balticum" occurred only sporadically in negligible quantities. In the Pomeranian Bight, the non-toxic species Pseudanabaena limnetica was observed at a concentration of 0.1 mm³/L.

Inner coastal waters of Mecklenburg-Vorpommern
Chlorophyll-a levels at the stations Lower Warnow, Strelasund, and Darß Lagoons, the only ones that could be sampled in winter, were rather low.
In the Strelasund waters, cryptoflagellates of the genera Plagioselmis and Teleaulax prevailed, besides the diatom Skeletonema costatum. They reached a biovolume of 0.2 mm³/L.
Also in March, chlorophyll-a levels in the Wismar Bight and at the stations in the Darß Lagoons were clearly below LMM. In the Salzhaff area, the chlorophyll-a value was 2.3 mg/m³. Heterocapsa rotundata reached a biovolume of 0.3 mm³/L. Chlorophyll-a levels in the Lower Warnow reached approximately 50 - 60 % of LMM. Small, unspecified centric diatoms (0.4 mm³/L) were the dominant algae. A lower chlorophyll-a level was also found in the Kubitzer Lagoon. The other stations of the monitoring network in the inner coastal waters could not be checked, mainly because of the long period of ice cover.
Also in April, the chlorophyll-a concentrations were below LMM. Chlorophyll-a levels in the Lower Warnow, Wismar Bight, and Darß Lagoons reached only 25 - 36 % of LMM.
The phytoplankton biovolumes ranged between 0.1 mm³/L in the Wismar Bight and Salzhaff, and 0.6 mm³/L in the Strelasund waters. In all inner coastal waters with an open connection to the Baltic Sea, Heterocapsa rotundata was found together with Cryptophyceae of the genera Plagioselmis and Teleaulax. In the Greifswald Lagoon and Strelasund, phytoplankton was dominated by Achnanthes taeniata (0.4 mm³/L and about 850,000 cells).
In May, chlorophyll-a concentrations in the Wismar Bight and Darß Lagoons were mostly below the long-term levels, as in the outer coastal waters. At the Lower Warnow monitoring stations, only 15 % and 23 % of the long-term mean for May was reached.
Phytoplankton was dominated by unspecified Chrysophyceae. Also small Cryptophyceae and the extremely small dinoflagellate Heterocapsa rotundata were found, although at very small biovolumes. Total biovolumes ranged between <0.1 and 0.7 mm³/L.
In June, chlorophyll-a in the waters between Lower Warnow and Peenestrom mostly reached normal levels. Locally, however, major deviations were found, e.g. in the Lower Warnow (10 times higher), Darß Lagoons (14 times), and Wismar Bight (4 times).
Biovolumes ranged between <0.1 mm³/L and 1.0 mm³/L. Large masses of microalgae in the Greifswald Lagoon, with an abundance of about 314 million cells/liter, produced a biovolume of as much as 0.9 mm³/L.
Above-average biomass was also observed in the Wismar Bight, at 0.9 mm³/L due to a mass development of flagellates (6.6 million cells/L) which probably belonged to the genus Chrysochromulina. Also in the inner coastal waters, blue-green algae were without significance.

Fish stocks

Observations made in the southern Mecklenburg Bight in January indicate that the number of cod in an active reproductive phase has decreased, continuing the downward trend.
Studies of spawning stocks in March showed that, for the first time in ten years, the conditions for cod spawning are expected to be very good, at least in the Arkona Sea and Bornholm Sea.
To protect cod stocks, the European Commission adopted emergency measures in April providing for a 1.5-month extension of the existing summer ban for all types of cod trawling, now covering the period from 15 April to 31 August.
At the end of April, investigations in the main cod spawning grounds in the western Baltic (Kiel Bight, Fehmarnbelt, Mecklenburg Bight, and Arkona Basin) showed extraordinarily favourable conditions for the development of cod eggs.

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