Cruise report from R/V Svea week 19, 2024

Type: Report
Author: Madeleine Nilsson


During the expedition, which is part of the Swedish pelagic monitoring program, the Skagerrak, the Kattegat, the Öresund and the Baltic Proper were visited. The expedition was combined with bottom fauna sampling in the Baltic Proper performed by Stockholm University (SU).

The temperature in the surface water was normal for the month and varied between 5 – 8 °C in the Baltic Sea and 9 – 11 °C in the Skagerrak and the Kattegat. In the Skagerrak and the Kattegat and further into the southern Baltic (the Arkona and Bornholm Basins) the salinity of the surface water was below normal, while it was higher than normal in the Eastern Gotland Basin.

The concentration of dissolved inorganic nutrients in the surface water has continued to decrease since March and April, but the concentrations of dissolved inorganic nitrogen (DIN) and silicate remained high and above normal at several stations in the Skagerrak and the Kattegat with levels up to 3.5 µmol/l and 6.2 µmol/ l respectively. In the Baltic Sea, the concentration of DIN was at low levels around 0.1 µmol/l, while the phosphate concentration was between 0.2 – 0.3 µmol/l, which was slightly elevated for the area around the Eastern- and Western Gotland Basins. The phosphate concentration was around 0.1 µmol/l in the Skagerrak and the Kattegat. In the Eastern Gotland Basin, the levels of silicate were slightly elevated and were between 10 – 16 µmol/l.

The oxygen situation in the bottom water was good (>4 ml/l) at all stations in the Skagerrak, the Kattegat and the Öresund, no lack of oxygen was observed.

In the Arkona Basin, the oxygen situation was good with concentrations around 4 ml/l in the bottom water. In the Bornholm Basin and the Hanö Bay, there is once again a severe lack of oxygen (<2 ml/l) in the deep water. In the Eastern Gotland Basin, severe oxygen deficiency occurred from about 70 m depth, while hydrogen sulphide was measured first at 125 m and deeper. Hydrogen sulphide occurred from 80 m in the Western Gotland Basin, but the levels are lower than in the Eastern Gotland Basin.

The next expedition with R/V Svea is planned for 2 – 8 June, starting in Kalmar and ending in Lysekil.