Cruise report from R/V Aranda week 28-29, 2017

Type: Report
Author: Karin Wesslander


Oxygen concentrations close to zero were observed in the deep water everywhere in the Baltic Proper except for in the Arkona Basin. Anoxic conditions, when hydrogen sulphide forms, were measured in the Western Gotland Basin from about 80 metres depth, in the Eastern Gotland Basin nearest the bottom at BY20 and at BY15 Gotlandsdjupet from 220 meters. At the previous expedition in June, hydrogen sulphide was present at the bottom at 4-CTRY-BP but now it was again oxygenated. Areas with acute hypoxia (dissolved O2 < 2 ml/l) were found in the Bornholm Basin at 80 meters and in the Eastern Gotland Basin and the Western Gotland Basin starting at around 70 metres. The nutrients DIN and DIP were generally depleted in the surface water which is normal at this time of year. In the southwestern Baltic Proper small amounts of phosphate was measured. Surface concentrations of silicate were still above normal in the Baltic Proper. The surface water temperature was normal for the season except from the Eastern Gotland Basin where it was colder than normal; the variations were 14.8-17.6 °C on the west coast of Sweden and between 12.9 and 16.5 °C in the Baltic Proper. The salinity in the surface water was normal except from the Skagerak where it was higher than normal. Salinity variations were 14.2-32 psu on the west coast and 6.4-8.0 psu in the Baltic Proper.