Monitoring cruise with r/v Gunnar Thorson in the Sound, Kattegat, Belt Sea and Arkona Sea, 13-16 September 1999. Cruise no. 192.

 

Report: Gunni Ærtebjerg
Cruise leader: Dorete Jensen.
Participants: Hanne Ferdinand, Peter Kofoed, Lars Renvald, Ole Manscher (13-14/9), Lars Aagesen (trainee), Jesper Poulsen (trainee).

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 September the water temperature during this cruise was 0.5-2° C higher, except for lower bottom water temperature in the Belt Sea. The surface salinity was lower and the bottom water salinity was higher than long term mean, except for higher surface salinity in Aalborg Bight, western Kattegat, due to up welling.

Since the cruise in August the minimum oxygen concentrations had decreased significantly, except in the Aalborg Bight. The lowest oxygen concentrations of 0.2-0.85 ml/l (4-13%) were observed in the Arkona Sea and southern Belt Sea. In the Sound, southern Kattegat and Laesoe Rende the minimum oxygen concentrations were 1.9-2.8 ml/l (31-44%). In the Great Belt the minimum concentration decreased from 2.8 ml/l (45%) in the north to 1.8 ml/l (29%) in the south.

 

Compared to September last year the minimum oxygen concentrations this year were lower. Compared to mean for September in the 1980s, when oxygen depletion often occurred, the minimum oxygen concentrations this year were also generally lower, except in the Sound and south-western Kattegat.

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 observed in the northwestern Kattegat, southern Kattegat, Great Belt and the Sound, and serious oxygen depletion was observed in the Arkona Sea and southern Belt Sea including the Kiel Bight, Fehmarn Belt and Mecklenburg Bight.

In figure 9 are shown the stations visited by Danish counties and NERI within the first three weeks of September 1999, and where oxygen depletion or serious oxygen depletion was observed.