Cruise report from R/V Svea week 15, 2025

Summary

During the expedition, which is part of the Swedish pelagic monitoring program, the Skagerrak, Kattegat, Öresund, and the Baltic Proper were visited. In addition to regular sampling, several special tasks were carried out, such as deployment of a bouy and changing of sensors at a mooring by Östergarnsholm, deployment of a bottom measurement system by L9 Laholmsbukten and sediment samplings carried out in the Baltic.

Due to high winds and rough seas, two stations in the northern Baltic (Huvudskär and BY29) could not be sampled, as well as a station in the Eastern Baltic (BY10).

Surface water temperatures were within normal range, or slightly above, in all sampled areas.
Additionally, a decrease of nutrients could be observed since the cruise in March, following the spring bloom now occurring in the marine areas.

The oxygen situation was generally good in Skagerrak, Kattegatt and Öresund, with no signs of oxygen deficiency noted. In the Baltic Proper it was only in the Arkona basin that good conditions in the bottom waters could be found.
In Hanö bay and BY5, acute oxygen deficiency (< 2 ml/l) was measured from 70 meters and below, with bottom waters showing nearly a complete lack of oxygen, anoxia. At station BY4 the oxygen levels had increased somewhat since March, with levels of around 3 ml/l.

In both of the basins in the Baltic Proper, acute oxygen deficiency occurred from a depth pf 60 – 80 meters and hydrogen sulphide was measured from a depth of 80 meters in the Western Gotland Basin, and 90 meters in the Eastern Gotland Basin.

Next cruise with R/V Svea is planned to start May 5th from Lysekil and conclude in Kalmar around May 12th.