Cruise report from R/V Aranda week 20-21, 2017

Type: Report
Author: Örjan Bäck


Oxygen concentrations close to zero were found in many parts of the Baltic Proper. Anoxic conditions, when hydrogen sulfide forms, were measured in the Western Gotland Basin from about 80 metres depth and in the Eastern Gotland Basin but only at BY15 Gotland Deep close to the bottom. Areas with acute hypoxia (dissolved O2 < 2 ml/l) were found from the Bornholm Basin to the Eastern Gotland Basin starting at around 70-80 metres and below, in the Western Gotland Basin already at 60 metres. Silicate concentrations were higher or much higher than the season mean in all areas. Dissolved inorganic nitrogen was more or less consumed in the upper water layers in the entire survey area, which is normal for the season. Concentrations of phosphate were also at normal levels; very low concentrations in the Kattegat and Skagerrak at around 0.1 μmol/l or below, a bit higher in the Baltic Proper, 0.15-0.5 μmol/l, where the highest values were found in the Western Gotland Basin. Surface water temperatures were normal in the entire survey area and varied between 10 to 11°C on the west coast and between 6 and 9 °C in the Baltic Proper. Surface salinity levels were slightly above normal in the Skagerrak and the Western Gotland Basin, normal levels were measured the remaining areas. A strong surface current was observed on the west coast at Å15 and at the stations to the east, also at the station Släggö, inside the archipelago, there was a strong surface current.