National Environmental Research Institute, Roskilde
Monitoring Cruise Report with r/v Gunnar Thorson; Cruise no.: 218 (15 - 19 September 2003)
Area: The Sound, Kattegat, Belt Sea and Arkona Sea
Since August the minimum oxygen concentrations had decreased, except in the northern Kattegat, but the concentrations this year are still significantly higher than at the same time last year. However, widespread oxygen deficiency (<2.8 ml/L) was observed in the southern Kattegat, the Sound, the Great Belt, the Mecklenburg Bight and the Arkona Sea, while severe oxygen deficiency (<1.4 ml/L) at the cruise was only observed in the Fehmarn Belt (1.1 ml/L). However, measurements made by Danish counties and German authorities showed widespread severe oxygen deficiency in the sea north of Funen, the southern Little Belt with associated coastal waters, western Kiel Bight, Lübeck Bight and Mecklenburg Bight. A report on oxygen deficiency in September 2003 is available at: http://iltrapport.dmu.dk (in Danish with an English summary).
At the cruise the temperature generally was higher than normal in the whole water column due to the warm summer. The salinity generally was lower than normal in the surface waters due to outflow from the Baltic Sea, but higher than normal in the bottom waters.
In the surface layer generally no inorganic nitrogen nutrients were present, while at least traces of phosphate were present in most areas. Silicate concentrations of 1 - 10 µmol/L were present in the surface water in all areas, except in the northern and central Kattegat.
In the bottom water nitrate concentrations above 6 µmol/L were observed only in the south-eastern Kattegat. In the Belt Sea the nitrate concentration in the bottom water was relatively low. Very high ammonium concentrations (4.0 - 9.5 µmol/L) were observed in the bottom water in the central Sound, the southern Great Belt and especially in the Mecklenburg Bight. High silicate and phosphate concentrations were observed in the bottom water east of Anholt, in the southern Great Belt and the Arkona Sea. High phosphate concentrations were also observed at the bottom in the Fehmarn Belt and Mecklenburg Bight.
The chlorophyll-a concentration in the surface water was relatively low (0.9 - 2.0 µg/L) in all areas, except in the Fehmarn Belt. However, in the western Kattegat and Great Belt a pronounced subsurface maximum of 3.9 - 8.4 µg/L was present in 10 - 15 m depth. In the eastern and southern Kattegat the highest concentrations (1.5 - 2.2 µg/L) were found in 15 - 20 m depth. In the Fehmarn Belt the highest concentrations (3.0 - 3.6 µg/L) were observed in the surface layer.
The complete report is to be found at: