National Environmental Research Institute, Roskilde, Dänemark
Monitoring Cruise Report with r/v Gunnar Thorson; Cruise no.: 222 (9 - 18 February 2004))
Area: Sund, Kattegat, Skagerrak, Nordsee, Belt See and Arkona See
The Jutland Coastal Current (JCC) with lower salinity and temperature and high nutrient concentrations, especially nitrate, was as usual evident but rather narrow along the Danish North Sea and Skagerrak coasts. The JCC also influenced the northern Kattegat north of Læsø with nitrate concentrations up to 13 - 14 µmol/L at salinities of 32 - 33. The JCC could not be traced south of Læsø and had thus not entered the Kattegat bottom water. In the Arkona Sea the bottom water salinity was as high as 20.2 due to an inflow from the Sound prior to the cruise. In the Kattegat, the Sound and the Belt Sea the temperature was above long-term mean, the stratification was relatively weak for the season, and generally the bottom water salinity was lower than normal, except in the Belt Sea.
In the North Sea the nutrient concentrations, except nitrite, as usual varied inversely to the salinity. Due to this
the nutrient concentrations were generally highest in the south-eastern German Bight (nitrate up to
38 µmol/L), decreasing to the north and west. Close to Hanstholm and Hirtshals and in the northernmost Kattegat nitrate concentrations of 10 - 15 µmol/L were observed in JCC water. Except for the northernmost Kattegat, the nitrate and DIN concentrations were relatively low in the rest of the Kattegat, the Sound, the Belt Sea and the Arkona Sea, probably due to decreased washout from land, and in the Great Belt partly due to a beginning phytoplankton spring bloom. Phosphate and silicate concentrations were about normal.
The DIN/DIP ratio varied from 25 - 35 in the German Bight to <10 at the north-western North Sea
stations and central Skagerrak stations. In the Kattegat and the Belt Sea the DIN/DIP ratio was rather close to the
Redfield ratio of 16 for phytoplankton uptake, as it varied from about 8 in the Arkona Sea to 18 in the northern Kattegat.
The phytoplankton spring bloom had not yet started in the North Sea, the Skagerrak, the Kattegat, the Sound and
the Arkona Sea, and the chlorophyll concentrations were generally low. However, the bloom had just started in parts of
the Belt Sea, especially at the border to the south-western Kattegat where a chlorophyll maximum of 4.5 µg/L was observed in the surface.
The minimum oxygen concentrations were about saturation level at all stations in the North Sea. At the deepest
station in the central Skagerrak the lowest oxygen concentration of 5.2 ml/L was observed in 150 - 175 m depth. In the Kattegat, the Sound and the Belt Sea the lowest oxygen concentration of 5.7 ml/L was found in the Sound. Compared to February last year, the minimum oxygen concentrations this year were generally higher. Last year the concentrations were unusually low, while the concentrations this year were about normal for February.
The complete report is to be found at: