Cruise report from R/V Svea week 19-20, 2026

Summary

During the cruise, which is part of the Swedish pelagic monitoring programme, the Skagerrak, Kattegat, the Sound, and the Baltic Proper were visited. During the cruise, Stockholm University conducted sediment and benthic fauna sampling in the Baltic Sea.

Surface water temperature was generally close to normal in all sea areas and had increased slightly since the April cruise. Salinity in surface waters was generally higher than normal in all areas.

Phosphate concentrations in surface waters were higher than normal in large parts of the Baltic Proper, as well as in the central Kattegat and parts of the Skagerrak. Dissolved inorganic nitrogen in surface waters was largely depleted, although stations with higher-than-normal concentrations occurred in all sea areas. Silicate concentrations in surface waters were generally higher than normal in all areas.

Oxygen conditions were good at all stations in the Skagerrak, Kattegat, and the Sound, and no oxygen deficiency was observed in these areas. The pulse of oxygen-rich water that reached the Hanö Bight and the Bornholm Basin in March/April had begun to be consumed, and oxygen concentrations had generally decreased in bottom waters compared to measurements in April. The inflow could be observed very weakly at intermediate depths in the Eastern Gotland Basin.

In deeper parts of the Baltic Proper, oxygen deficiency or anoxic conditions persisted, with the presence of hydrogen sulphide from approximately 80–100 m depth.

Chlorophyll fluorescence was relatively high in association with the stratification. Sharp and pronounced fluorescence peaks were observed at several stations in the Skagerrak and Kattegat. Biological activity in the form of fluorescence was also observed in the Baltic Proper in the surface layer down to the thermocline. High fluorescence peaks were also observed deeper in the water column, around the depth of the oxycline. This is likely caused by different types of hydrogen sulphide bacteria living at the interface between oxygenated and anoxic water, which can fluoresce.

SMHI’s next regular cruise with R/V Svea is planned for 12–17 June, starting in Lysekil and ending in Kalmar.