Report: Gunni Ærtebjerg
Cruise leader: Gunni Ærtebjerg/Martin Larsen
Participants: 7-15/8: Gunni Ærtebjerg, Lars Renvald, Jan Damgaard, Susanne
Hemmingsen;
7-18/8: Dorete Jensen, Hanne Ferdinand, Peter Kofoed;
7-8/8: Ole Lund Jensen, Tommy Nielsen (DFU); 15-18/8: Martin Larsen.
This report is based on preliminary data, which might later be corrected. Citation permitted only when quoting is evident. This file contains the summary only. To get the full report, click here. This file is in Adobe Acrobat ™ format. If you do not have a a Adobe Acrobat ™ Reader, click here, to download
Low saline water was spread out on the surface in the Skagerrak and eastern North Sea. In the North Sea a pycnocline was present only at the westernmost and northernmost stations. At these stations the minimum oxygen concentration was 4-5 ml/l. Generally, nutrients in the surface water were only observed in the German Bight. However, traces of nitrate, nitrite and silicate were also present along the Danish North Sea coast. Blooms of Noctiluca miliaris were observed in the German Bight as deep orange coloured stripes on the surface.
In the Kattegat, Sound and Belt Sea the stratification was strong, except in shallow areas. An upwelling was indicated in the western Kattegat, where traces of nitrate were observed in the surface water. Cold and unusually salty bottom water (34.1-34.5 psu) was present in the eastern Kattegat. In the surface water ammonium was observed in the Sound and Great Belt. Phosphate and silicate were present in the western Kattegat, Sound, Belt Sea and Arkona Sea. The chlorophyll was relatively homogeneously distributed in the uppermost 15 m of the water column, and no pronounced subsurface maximum was observed.
The lowest oxygen concentration of 0.6 ml/l (9%) was observed in the Fehmarn Belt, increasing to 1.6 ml/l (23%) at Gedser Rev and 1.8 ml/l (25%) in the deeper part of the Arkona Sea. In the Sound 1.7 ml/l (25-27%) was observed in the whole water column from 30 m depth to the bottom in 51 m depth. In the southern Kattegat the minimum concentrations varied between 2.5 and 3.3 ml/l (39-49%), lowest at the entrances to the Sound and Belt Sea. In the Great Belt the minimum oxygen concentration decreased from 2.5 ml/l (39%) in the north to 2.3 (36%) in Langelands Belt.
Compared to August last year and to mean for August in the 1980’s the minimum oxygen concentrations this year are lower in the Sound, Great Belt, Fehmarn Belt, western Kattegat and east of Anholt. The minimum oxygen concentrations in the Arkona Sea were lower than in the 1980’s. Thus, low oxygen concentrations occur this year earlier than usual.
In Denmark oxygen depletion is defined as minimum oxygen concentrations below 2.8 ml/l (4 mg/l), and serious oxygen depletion as below 1.4 ml/l (2 mg/l). From these definitions serious oxygen depletion occurred in the Fehmarn Belt, and oxygen depletion occurred in the south-western Kattegat, the Sound, Great Belt, Mecklenburg Bight, Gedser Rev area and Arkona Sea. In figure 20 is shown the stations where oxygen depletion and serious oxygen depletion was observed by Danish counties and NERI within the first 3 weeks of August 2000.