Summary
During the cruise, which is part of the Swedish pelagic surveillance program, the Skagerrak, the Kattegat, the Sound and the southern parts of the Baltic Proper were visited. In the Baltic Proper, nutrient mapping was carried out.
The warming of the surface water continued in all sea areas and was within the normal range at most stations, the temperature in the surface water varied between 13–16 degrees, it was warmest in the Kattegat and coldest in the Baltic Proper. The salinity of the surface water was above normal at several stations in the Skagerrak and Kattegat but only at a few stations in the Baltic Proper.
The concentrations of nutrients in the surface water were generally low, as biological production assimilate most of the nutrients into organic material during the summer. At the vast majority of stations, the concentrations were within the normal range and for dissolved inorganic nitrogen, the concentration was below the reporting limit at all but three stations. Phosphate concentrations were highest in the southern Baltic Proper and lowest in the Skagerrak.
In the deep water in the Eastern and Western Gotland Basins, very high concentrations of ammonium were measured, approximately twice as high as the average value for the period 1991–2020.
The oxygen situation The Baltic Proper remains poor. Hydrogen sulphide was measured from 70–80 m in the Eastern and Western Gotland Basins, in Bornholm Basin and Hanö Bight acute oxygen deficiency was measured from 70 m. In the Eastern Gotland Basin there is a layer with low or immeasurable levels of hydrogen sulphide between 80–130 m while in the Western Gotland Basin it increases to high levels of hydrogen sulphide directly at 70 m.