Cruise report from R/V Aranda week 37-38, 2019

Type: Report
Author: Örjan Bäck


The surface temperature was normal for the season and varied between 14.5 - 17.5 ° C in the upper water mass. In the Baltic, there was a strong thermocline throughout the area, usually at about 30 meters depth with cold underlying water, in the Kattegat the temperature in the underlying water was not as cold. The salinity was slightly higher than normal in the surface of the Kattegat and the southwestern Baltic, while in the Gotland basins it was at normal values with slightly higher levels in the deep water.
The levels of nutrients in the surface water were low, which is normal just after summer. Dissolved inorganic nitrogen was depleted down to the halocline both in the North Sea and in the Baltic, while phosphate was still present in small amounts in surface water.
In the Baltic Proper, acute oxygen deficiency (<2ml/l) prevailed at the bottom of the Arkona Basin and oxygen-free conditions with hydrogen sulphide closest to the bottom of the Hanö Bay and Bornholm Basin. In the Gotland basins, oxygen was close to 0 ml/l from about 70 meters depth and hydrogen sulphide was found at all stations, at BY38 already at 60 meters. At BCSIII-10 in the south-east, no hydrogen sulphide was found and the oxygen content never dropped below 2ml/l.