Cruise report from R/V Svea week 32-33, 2022

Type: Report
Author: Karin Wesslander


The Skagerrak, the Kattegat, The Sound and the Baltic Proper was visited during this cruise, which is part of the national marine monitoring programme of Sweden.

The temperature in the surface water was normal in the Skagerak and Kattegat, where it varied between 17 and 20 degrees. In the Baltic Sea, it was warmer than normal in the Western and Eastern Gotland basins, and the temperature there reached up to 21 degrees. The surface salinity was normal in the Skagerak and Kattegat, but in the Baltic Sea it was above normal at several stations.

Dissolved inorganic nitrogen was depleted in all sea areas down to the pycnocline. There were also low levels of phosphate in the surface water, although it was not completely exhausted. These low levels of nutrients are normal for the season. There were also mostly normal levels of silicate, highest in the Baltic Sea and significantly lower levels in the Skagerak and Kattegat.

There is now acute oxygen deficiency, < 2 ml/l, at all visited stations in the Baltic Proper except at the southern tip of Öland and it is a deterioration from last month. In the Arkona Basin, the oxygen concentration decreased rapidly from 40 m and there was acute oxygen deficiency closest to the bottom. In the Bornholm Basin, acute oxygen deficiency was noted from 70 m and hydrogen sulphide was observed from 80 m. In Hanö Bay, hydrogen sulfide was already noted from 70 m. In the Western and Eastern Gotland basins, there was acute oxygen deficiency from 60 – 70 m and hydrogen sulfide was measured from 70 – 80 m. Below 125 m at the Gotland Deep in the Eastern Gotland Basin, the hydrogen sulfide concentration increased rapidly to very high levels.

Closest to the bottom in the Skagerrak, there was oxygen deficiency at Släggö (3.1 ml/l), in the Kattegatt there was oxygen deficiency at Fladen (3.6 ml/l) and Anholt E (3.1 ml/l) and in Öresund it was also oxygen deficiency (3.7 ml/l).