Cruise report from R/V Svea week 16, 2020

Type: Report
Author: Johan Kronsell


Sea surface temperatures were above normal at all stations sampled in the Baltic Proper, and normal in the Sound, the Kattegat and the Skagerrak. The temperature varied from slightly below 5°C in the northern Baltic Proper up to 7.2°C in the Sound. In the Baltic Proper and the Sound the sea surface salinity was above normal.

Concentrations of dissolved inorganic nitrogen, DIN, at the surface were normal for the season at all stations except at N14 Falkenberg in the Kattegat where concentrations were normal. The silicate concentrations were above normal at most of the stations. Levels of dissolved inorganic phosphorus, DIP, were normal or above normal in the surface except in the Sound were levels were below normal.

Oxygen concentrations in the Arkona Basin were good, and measured minimum concentration in the bottom water was 5.2 ml/l. In the Bight of Hanö, the Bornholm Basin and in the southeastern part of the Baltic Proper, the oxygen concentration in the bottom water had continued to decrease. In March it was above 2 ml/l, which is the limit for acute hypoxia, and in April it was 1.4-1.7 ml/l. In the Eastern Gotland Basin acute hypoxia was found from about 65 meters depth, a little deeper in the northern part. In the Western Gotland Basin acute hypoxia was found from 75-80 meters.

Anoxic conditions, when when hydrogen sulphide can form, were found in the Eastern Gotland Basin from 125 meters depth, and in the Western Gotland Basin from 100 meters depth.