Cruise report from R/V Aranda week 24-25, 2017

Type: Report
Author: Örjan Bäck, Martin Hansson


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, but only at BY15 Gotlandsdjupet close to the bottom and at 70 metres depth at 4-CTRY-BP, below 70 metres the oxygen concentration increased towards the bottom. Areas with acute hypoxia (dissolved O2 < 2 ml/l) were found in the Bornholm Basin, the Eastern Gotland Basin and the Western Gotland Basin starting at around 70 metres. Concentrations of Silicate above the halocline in the entire Baltic Proper continues to be higher than normal, with values between 12-17 μmol/l. In the remaining areas normal concentrations were observed. The nutrients (dissolved inorganic nitrogen, DIN, and phosphorous, DIP) were generally depleted in the surface waters which is normal for the season, some available phosphate were measured in the south western Baltic Proper. Nutrient concentrations in deeper water were at normal levels, an exception was the bottom water at Fladen were unusually high values of both DIN and DIP were found, together with low oxygen concentrations this indicates degradation of organic material which consumes oxygen and releases nutrients. The surface water was normal for the season in the entire survey area and varied between 15 and 17 °C on the west coast of Sweden and between 11 and 16 °C in the Baltic proper. The salinity in the surface water was higher than normal in the Sound with 18 psu and normal in all other areas, 20-31 psu on the west coast and around 7 psu in the Baltic.