Cruise report from R/V Svea week 20-21, 2022

Type: Report
Author: Johan Kronsell


During the expedition, which is part of the Swedish national marine monitoring programme, the Skagerrak, the Kattegat, the Sound and the Baltic Proper were visited.

Warming of the surface water had continued since last expedition in all the visited sea areas. In the Skagerrak, the Kattegat and in the southern basins of the Baltic Proper, the surface water temperature was higher than normal for the season. Salinity in in the surface water was higher than normal in large parts of the Baltic Proper while normal values were measured in the Kattegat and the Skagerrak.

Concentrations of nutrients in the surface water were generally low above the halocline where biological production had consumed available nutrients. The silicate concentrations were above normal in several of the Baltic Proper basins and generally normal in the Kattegat and the Skagerrak.

The oxygen situation continues to be bad in most of the Baltic Proper, only in the Arkona Basin was the bottom water well oxygenated. In the Hanö Bay and the Bornholm Basin, hydrogen sulphide was again present in the bottom water. The station in the southeastern Baltic Proper could not be visited in May.

In the Western and Eastern Gotland Basins, oxygen-free conditions were found from depths exceeding 70-90 metres and concentrations of hydrogen sulphide remained at record high levels at several stations. Acute oxygen deficiency (< 2ml O2/l) was found from 80 metres depth in the Eastern Gotland Basin and in the Western Gotland Basin oxygen concentration at 60 metres was good but already at 70 metres depth, hydrogen sulphide was detected.

Chlorophyll fluorescence measurements done with the CTD showed low plankton activity in all sea areas, only a few stations had fluorescence peaks indicating a bit higher plankton activity.