Cruise report from R/V Svea week 6-7, 2023

Type: Report
Author: Lena Viktorsson


During the expedition, which is part of the Swedish pelagic monitoring program, the Skagerrak, Kattegat, the Sound and the Baltic Sea were visited. In the Baltic Proper, the annual mapping of nutrients was also carried out.

Due to severe weather during the first day of the expedition, two stations in the Skagerrak could not be sampled. After the expedition entered the Baltic Proper, the weather was mostly calm and all stations included in the nutrient mapping were sampled.

The concentration of nutrients in the surface water remained at high winter levels in all sea areas except in the Kattegat where the nutrients had begun to decrease and increased activity of phytoplankton was reflected in chlorophyll fluorescence. In the Baltic Proper, the concentration of phosphate and silicate in the surface water was normal, while the levels of dissolved inorganic nitrogen were below normal. In the deep water of the Baltic Proper, the concentrations of nutrients and hydrogen sulphide remained very high. In the Eastern and Western Gotland basins, it was anoxic from 70–80 m. In the Eastern Gotland basin, hydrogen sulphide concentrations increased rapidly below 125 m depth to record high levels. In the Northern Baltic Proper it was anoxic from 90–100 m and here and in the Western Gotland Basin the levels of hydrogen sulfide and nutrients were lower than in the Eastern Gotland Basin, but also here above normal. Above all, the levels of ammonium were well above normal in the deep water of the Baltic Proper.

SMHI’s next regular expedition with R/V Svea is planned for 9 – 15 March.