Monitoring cruise with r/v Gunnar Thorson in the Sound, Kattegat, Belt Sea and Arkona Sea, 8-11 November 1999. Cruise no. 194

 

Report: Gunni Ærtebjerg
Cruise leader: Jan Damgaard.
Participants: Dorete Jensen, Hanne Ferdinand, Peter Kofoed, Britta Pedersen (8-9/11), Ole Jensen (8/11)

 

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

Summary

Compared to long term monthly mean (1931-1960) for November the temperature during this cruise was 0-2° C higher, both in the surface and the bottom water. The surface salinity was in the Kattegat and Fehmarn Belt generally lower, while the bottom water salinity all over was higher than long term mean.

Nitrate was present (>0.2 m M) in the surface layer only in the Sound and Great Belt. Except in the eastern Kattegat traces of phosphate (>0.05 m M) were observed all over in the surface layer. Also silicon (>1 m M) was found in the surface water, except in the northern and eastern Kattegat.

The mean chlorophyll-a concentration in the uppermost 15 m was relatively high and ranged from 2.0 m g/l in the Sound to 10.4 m g/l in the south-western Kattegat. The highest concentration of 20.2 m g/l was found in a narrow sub-surface layer at 10 m depth in the south-western Kattegat. Otherwise, the chlorophyll was fairly evenly distributed in the uppermost 10 m and lower at 15 and 20 m depth.

Since the cruise in October the minimum oxygen concentrations had increased, except in the northern and western Kattegat, Great Belt and the Gedser Rev area. The lowest oxygen concentration of 2.5 ml/l (42% saturation) was observed in the Sound. In the southern-most Kattegat and the Great Belt the minimum concentrations were 3.1-3.9 ml/l (52-61%). Also at Gedser Rev the minimum oxygen concentration was still relatively low (3.4 ml/l, 52%).

Compared to November last year the minimum oxygen concentrations this year were lower in the Sound, southern-most Kattegat and Fehmarn Belt. Compared to mean for November in the 1980s, except for the Arkona Sea, the minimum oxygen concentrations this year were generally lower, especially in the Belt Sea.

Oxygen depletion is in Denmark defined as below 2.8 ml/l (4 mg/l) and serious oxygen depletion as below 1.4 ml/l (2 mg/l). From these definitions oxygen depletion was during the cruise still present in the Sound.