National Environmental Research Institute, Roskilde
Monitoring Cruise Report with r/v Gunnar Thorson; Cruise no.: 221 (10 - 14 November 2003)
Area: The Sound, Kattegat, Belt Sea and Arkona Sea
Oxygen depletion (<2.8 ml/L) still occurred in the northern Great Belt, and also in the southern Great Belt; the minimum oxygen concentration was quite low (2.9 - 3.0 ml/L, 45 - 47 % saturation). In the Great Belt, the Fehmarn Belt and the Mecklenburg Bight the minimum oxygen concentrations were lower than at the same time last year, and in all areas except the Sound and the Arkona Sea lower than averages for November in the 1980's.
The surface temperature was about average for the season, while the bottom water temperature was 0.6 - 3.2 °C higher than normal. The surface salinity was much lower than average (2.5 - 6.1 psu), except in the Aalborg Bight, while the bottom water salinity was generally higher than normal. The southern Belt Sea bottom water deviated from this pattern with temperature and salinity lower than normal.
Generally, the stratification was relatively strong for the season, especially in the Great Belt.
The hydrography witnesses to dominating calm weather and southerly wind conditions, surface outflow from the Baltic Sea, and rather stagnant bottom water. The autumn renewal of the bottom water with oxygen rich Skagerrak water had not yet taken place.
In the surface layer the nitrate concentration was still quite low (0.1 - 1.0 µmol/L) in most areas, except in the western Kattegat. Ammonium concentrations of 0.2 - 1 µmol/L were observed in the surface in most areas. Phosphate concentrations of 0.1 - 0.6 µmol/L and silicate concentrations above 3 µmol/L and up to 11 µmol/L were present in the surface water in all areas.
In the bottom water the highest concentrations of nitrate (7 - 10 µmol/L), phosphate (1.0 - 2.0 µmol/L) and silicate (25 - 30 µmol/L) were observed in the Great Belt, that is in the area with the lowest oxygen concentration. The highest concentrations of ammonium (2.0 - 3.5 µmol/L) and nitrite (>0.8 µmol/L) were found in the southern Belt Sea and the Mecklenburg Bight, respectively.
The chlorophyll-a was quite evenly distributed in the surface layer where the concentrations in the uppermost 10 m varied between 1.2 and 2.8 µg/L with the lowest concentrations in the Sound and the Mecklenburg Bight.
The complete report is to be found at: