Monitoring cruise with r/v Gunnar Thorson in the Sound, Kattegat, Belt Sea and Arkona Sea, March 13th-17th, 1995.


Cruise leader: Jan Damgaard

Participants: Dorete Jensen, Hanne Ferdinand, Susanne Hemmingsen, Kjeld Sauerberg, Christina Hansen; Monique Hedderson and Jonathan Pundsack (guests from USA)

General

The route, time schedule and stations of the cruise are shown in figure 1. Besides the pelagic monitoring measurements, macrozoobenthos was sampled at the stations 939, 952 and 444, and sediment for chlorophyll determination was sampled at station 413. Yellow substance was measured spectrophotometrically at all water samples.

The monthly mean temperature in February was in Denmark 3.7 oC above mean for the period 1961-90 and the precipitation was 86% above normal. The wind was relatively strong, mostly from southwest and west (Danish Meteorological Institute). The precipitation during the winter December 1994-February 1995 have in Denmark been about 80% above normal.

Hydrography

The surface temperature ranged from 2.9 oC in the Arkona Sea to 3.5 oC in the southern Kattegat (Fig. 3, 5). The surface salinity had decreased significantly since mid February, in the Great Belt with more than 9 psu. The bottom water salinity ranged from 9.2-12.2 psu in the Arkona Sea to 34.68 psu in the northeastern Kattegat. The bottom water salinity had increased since mid February in the eastern and northern Kattegat and in the central Great Belt, but decreased in the western Kattegat, southern Belt Sea and in the Arkona Sea. The salinity stratification was relatively strong for the season, except for a nearly homogenous water column at station 443 in the southern Great Belt. The strongest salinity stratification was 19-22 psu in the Sound and 16 psu in the central Great Belt.

Compared to long term monthly means (1931-60) for February both the surface and bottom water temperatures during this cruise were generally higher, except in the bottom water in the southern Kattegat. The salinities were both in the surface and the bottom water much lower than normal, except in the north-western Kattegat (St. 403).

Oxygen

The minimum oxygen concentrations were generally high and with a few exceptions above 90% saturation. The lowest saturation (79%, 6.8 ml/l) was found at the bottom in the Arkona Sea (St.444). In the Fehmarn Belt 83% (6.9 ml/l) was found, and in the Sound (St. 431) and southern Kattegat (St. 922) the minimum oxygen concentrations were 85-86% (6.2-6.4 ml/l).

Compared to mean for February in the 1980's the minimum oxygen concentrations this year are generally a little higher, except in the Fehmarn Belt and the Arkona Sea.

Nutrients

In the bottom water the nitrate concentrations were below 10 mol/l only in the southwestern and western Kattegat, the southern Belt Sea and the Arkona Sea ( 7, 9). In the northern and eastern Kattegat and into the Sound the Jutland Coastal Current had added nitrate rich water of 30-34 psu salinity with up to 18 mol/l (Fig. 11).

The concentrations of nitrite, ammonium and silicate along a transect from the northern Kattegat through the Great Belt and Fehmarn Belt to the Arkona Sea are shown in the 13andBack to Department of Marine Ecology and Microbiology