Cruise report from R/V Svea week 42, 2022

Type: Report
Author: Johan Kronsell


During the expedition, which is part of the Swedish national marine monitoring programme, the Skagerrak, the Kattegat, the Sound and the Baltic Proper were visited.

Cooling of the surface water had continued in all sea areas visited, and the sea surface temperature was 3-4 degrees lower compared to the previous expedition. At most stations the surface temperature was normal for the season. The salinity in the surface water of the Kattegat and the Skagerrak was normal for the season, but at several stations in the Baltic Proper sea surface salinity was slightly above normal.

Concentrations of nutrients in the surface water were generally normal for the season above the halocline. However, in the Kattegat, levels of both phosphate and silicate were slightly below normal at several stations.

The oxygen situation continues to be very bad in most parts of the Baltic Proper, only in the Arkona Basin was the bottom water well oxygenated. In the Hanö Bight and at the station in the south-eastern Baltic Sea, there was acute oxygen deficiency (< 2ml O2/l) from depths of 70 and 80 metres, respectively, but no hydrogen sulphide was found. In the Bornholm Basin, there was acute oxygen deficiency from a depth of 70 meters, and hydrogen sulphide was found at 80 meters at BY5.

In the Western Gotland Basin, hydrogen sulphide was found at a depth of 70 meters at one of the stations. And in the Eastern Gotland Basin, oxygen-free conditions were measured at a depth of 80 meters, and hydrogen sulphide was detected at 90 meters depth. At the stations in both the Eastern and the Western Gotland Basin, levels of hydrogen sulphide were higher than normal in the deep water.

Fluorescence measurements from the CTD indicated low plankton activity down to the thermocline in all visited sea areas.