Cruise report from R/V Svea week 42-43, 2023

Type: Report
Author: Martin Hansson


During the cruise, which is part of the national marine monitoring programme of Sweden, oceanographic environmental monitoring was performed in the Skagerrak, the Kattegat, the Sound and the Baltic Proper.

The conditions in the sea areas around Sweden were largely influenced by the storm that passed over the region before and during the cruise. The strong easterly wind led to significant mixing of the surface water, resulting in a cooling effect and lower temperatures than normal were recorded. The salinity of the surface water was also higher than usual in many areas, indicating strong wind-induced mixing. Nutrient levels also showed higher concentrations than normal in large areas of the Baltic Proper. A similar situation was observed in the Skagerrak.

In the deep basins around Gotland, nutrient concentrations remained much higher than normal, reflecting the poor oxygen conditions and record-high concentrations of hydrogen sulphide in the deep areas. In the Western Gotland Basin, oxygen-free conditions were noted from a depth of 70 meters, and in the Eastern Gotland Basin, the corresponding depth was about 80 meters.

In the southeastern Baltic Proper, no hydrogen sulphide was noted at the bottom, but a weak pulse of oxygenated water (~1.5 ml/l) was observed at around 80 meters depth. In the Bornholm Basin and Hanö Bay, oxygen conditions near the bottom were oxygen-free, with oxygen deficiency noted from a depth of 60-70 meters.

During September, the oxygen conditions near the bottom in the Arkona Basin were very poor, with oxygen levels near zero. By October, the conditions had improved considerably, although oxygen deficiency was still noted in the eastern parts.

Technical problems during the cruise prevented the use of the regular CTD rosette throughout the entire expedition. Backup equipment had to be used, leading to the absence of certain depths and analyses in the southern Baltic Proper, as well as in the Skagerrak and Kattegat.

The next regular cruise is scheduled to start on 10th November and will start in Falkenberg and end in Kalmar.