Cruise report from R/V Svea week 6-7, 2026

Summary

During the expedition, which is part of the Swedish pelagic monitoring programme, the Skagerrak, the Kattegat, the Sound and the Baltic Proper were visited. In the Baltic Proper, nutrient mapping was carried out.

Surface water temperatures were below normal in the Skagerrak and the Kattegat, ranging from -0.5 to 1°C, whereas in the Baltic Proper they were within the seasonal norm, ranging from 1 to 3.5°C.

In the Skagerrak, the salinity was decreased to approximately 22 psu, due to a longer period of persistent strong easterly winds. Concentrations of dissolved inorganic nutrients in the surface layer had declined and were below the monthly average. In the Kattegat, concentrations of dissolved inorganic nitrogen (DIN) were also below normal and had decreased since January, while silicate and phosphate concentrations remained largely unchanged.

Oxygen conditions were good at all stations in the Skagerrak, the Kattegat and the Sound, and no hypoxia was observed.

In the Baltic Proper, nutrient concentrations had increased at most stations since January. DIN concentrations were within the normal range, whereas phosphate and silicate concentrations were above normal throughout the Baltic Proper.

In the Arkona Basin, bottom-water oxygen conditions were good and concentrations had increased slightly since January. In the Bornholm Basin, acute hypoxia was recorded, with concentrations below 1 ml/l. In the Eastern Gotland Basin, anoxic conditions prevailed, with hydrogen sulphide detected from 90 m depth and acute hypoxia occurring from 75 m. In the northern Baltic Proper, anoxia was observed from 80–90 m and acute hypoxia from 75 m. In the Western Gotland Basin, the depth of anoxia and acute hypoxia varied from 80 m and 70 m, respectively, at BY31 to 100 m and 90 m, respectively, at BY38.

SMHI’s next regular expedition with R/V Svea is scheduled for 8–14 March, departing from Kalmar and concluding in Gothenburg.