Cruise report from R/V Svea week 10-11, 2026

Summary

During the cruise, which is part of the Swedish pelagic monitoring programme, stations were visited in the Skagerrak, Kattegat, the Sound, and the Baltic Proper.

Surface water temperatures were generally close to normal in all sea areas and ranged between 1.8 and 4.1 °C. Salinity was generally higher than normal in the Baltic Proper and normal in the Kattegat. In the Skagerrak, variability was large, with observations of normal, lower-than-normal, and higher-than-normal salinity.

Concentrations of dissolved inorganic nitrogen were generally normal for the season in all basins. Phosphate concentrations were higher than normal in the northern Kattegat and southern Skagerrak, in the Sound, and in large parts of the Baltic Proper. Silicate concentrations were above normal throughout the Baltic Proper and in the southern Skagerrak. In the central Kattegat, concentrations were lower than normal, likely due to high biological production.

The oxygen situation was good at all stations in the Skagerrak, Kattegat, and the Sound, with no oxygen deficiency observed in these areas.

In the Arkona Basin, bottom waters were well oxygenated, indicating inflow from the Kattegat via the Sound and the Danish Straits. In the Bornholm basin, at BY4 and BY5, an inflow had reached the bottom water and increased oxygen concentrations near the seabed, although the inflowing water was only observed within the deepest 5–10 metres above the bottom. In the deeper parts of the Baltic Proper, oxygen deficiency or anoxic conditions persisted, with hydrogen sulphide present from approximately 80–100 m depth.

Fluorescence measurements generally indicated low biological activity, except in the Arkona Basin where several layers of plankton activity were observed.

SMHI’s next regular cruise with R/V Svea is planned for 7–12 April, starting in Kalmar and ending in Gothenburg.