Cruise report from R/V Svea week 23, 2020

Type: Report
Author: Karin Wesslander


The surface water temperature varied between 10-16 °C, which is normal for the season. At most stations in the Baltic Proper, the temperature in the entire depth profile was above normal. The cooling that normally occurs during winter was 2019/2020 very weak. The salinity in the Baltic Proper was above normal at all stations visited, both in the surface and in the deep water.  

Dissolved inorganic nitrogen in the surface water was below detection limit from the surface to 2040 m in all sea areas, which is normal after the spring bloom. Phosphate levels were higher than normal in the Baltic Proper except from the Western Gotland Basin. The silicate levels were above normal at most stations visited in the Kattegat and the Baltic Proper and also at some stations in Skagerrak.  

The oxygen situation in the Baltic Sea continues to be severe. Completely oxygen-free conditions, when toxic hydrogen sulphide is formed, were found in the Western and Eastern Gotland Basin from 80-90 meters deep. Acute oxygen deficiency (<2 ml/l) was found from 70-80 meters depth throughout the area. In Hanö Bight and in the Bornholm Basin, oxygen levels in the bottom water have continued to decline. In March they were above 2 ml / l, which is the limit for acute oxygen deficiency, and during this expedition in June about 0.4 ml / l. The oxygen situation was good in the Skagerrak and Kattegat.
The inflow that occurred in November/December 2019 was still visible at the southeastern Baltic Proper. Oxygen levels just above 1.0 ml/l were observed close to the bottom at BCSIII-10 and at intermediate depth, 80-125 meters, at BY10.