Cruise report from R/V Svea week 24-25, 2026

Summary

This expedition, conducted within the Swedish pelagic monitoring programme, covered the Skagerrak, the Kattegat, the Sound and the Baltic Proper.

Sea surface temperatures were close to the seasonal norm in the Skagerrak, the Kattegat and the Sound, and above the norm in the Baltic proper, ranging between 13.2 and 16.2°C, with the highest temperatures recorded in the Kattegat. The sea surface salinity was within the seasonal norm in the Skagerrak, the Kattegat and the Sound, and above the norm in the Baltic Proper.

Concentrations of dissolved inorganic nitrogen (DIN) and phosphate in surface waters were low, which is typical for this time of year. Surface-water silicate concentrations were low in Skagerrak, which is normal for the season, and slightly above the seasonal norm at a majority of the stations in the Baltic Proper.

Oxygen conditions in the Baltic Proper remain poor. Good oxygen conditions were only observed in the southern areas, including the Arkona Basin, the Bornholm Basin and at station BY39. Acute oxygen deficiency, defined as oxygen concentrations below 2 ml/l, was observed from depths of 60–80 m in both the Western and Eastern Gotland Basins, except at the shallow station BY39. Hydrogen sulphide was detected from 70–80 m depth in the Western Gotland Basin and from 80–145 m depth in the Eastern Gotland Basin.

Several stations in the Baltic Proper exhibited pronounced chlorophyll fluorescence maxima between 15–20 m depth. In the Kattegat, elevated fluorescence peaks were observed between 20 and 30 m depth. Surface accumulations of cyanobacteria were observed east of Gotland. Further information on the phytoplankton situation is available in the June Algaware report.

https://www.smhi.se/publikationer/publikationer/algrapporter External link.

The next regular monitoring cruise is scheduled to commence in Lysekil on 10 July and conclude in Lysekil on 16 July.