Cruise report from R/V Svea week 2-3, 2026

Summary

During the cruise, which is part of the Swedish pelagic monitoring programme, stations in the Skagerrak, Kattegat, Öresund and the Baltic Proper were visited. In the Kattegat, the yearly survey of the winter nutrient pool was conducted.

The temperature in the surface water was normal for the month in the Skagerrak, Kattegat, the Arkona Basin and the Hanö Bay, while it was warmer than normal int the rest of the Baltic Proper. The lowest surface water temperature was recorded in the Kattegat, ranging between 2–4 °C. In the Skagerrak, temperatures varied between 4–8 °C, and in the Baltic Proper they were around 5 °C. Surface water salinity was mostly normal for the month, slightly lower in the Öresund and slightly higher in the Eastern Gotland Basin.

The concentration of dissolved inorganic nitrogen (DIN) was below normal in most parts of the Kattegat, the Öresund, the Arkona Basin and the Western Gotland Basin. In contrast, phosphate and silicate concentrations were above normal in most parts of the Baltic Proper.

The oxygen conditions in the bottom waters were good in the Skagerrak and the Kattegat, with concentrations varying between 4–8 ml/l. In the Baltic Proper, severe hypoxia (< 2ml/l) was observed in all basins except the Arkona Basin. Hydrogen sulphide (H2S) was detected from 80 m in the Eastern Gotland Basin, except at station BY15, where it was first detected at 140 m. In the Western Gotland Basin H2S was measured from 90 m.

Upcoming cruises with R/V Svea include the International Bottom Trawl Survey (IBTS) from 18 January to 1 February, led by SLU Aqua. IBTS will depart from and return to Lysekil, with SMHI participating to collect CTD profiles at each trawl and to continue the winter nutrient pool survey. SMHI’s own expedition is scheduled from 4 to 11 February, departing from Lysekil and ending in Kalmar.