Summary
The cruise was initially delayed for some hours, and there were some problems with the generators resulting in inability to maintain full speed of the vessel during the cruise. Shortly before arriving Lysekil, information was given stating that other bookings of R/V Aranda had priority, and the remaining stations were cancelled. Due to this, large parts of the Baltic Proper were not sampled during the cruise, which was SMHI’s first on board R/V Aranda since July 2017.
The sea surface temperature in the areas monitored was normal or below normal for the season. At most stations the temperature was between 14 and 16°C. At the coastal station Ref M1V1 in the southern part of Kalmarsund the temperature was only slightly above 11°C. The salinity in the surface water was normal for the season in the Skagerrak and at BY29 in the Northern Gotland Basin, but above normal at all other stations. In the Western Gotland Basin also the salinity in the deep water was above normal levels.
Anoxic conditions, when hydrogen sulphide can form, were found in the Western Gotland Basin from about 70-80 meters depth. In the Bight of Hanö hydrogen sulphide was found from 70 meters depth. In the Arkona Basin, no hydrogen sulphide was found, but at the station BY2 the oxygen concentration at the bottom was almost zero.
Nutrients in the form of dissolved inorganic nitrogen, DIN, in the sea surface were below reporting limit at most stations in the Baltic Proper and the Kattegat. Concentrations of dissolved inorganic phosphorus, DIP, in the surface water were normal for the season at almost all stations. Silicate concentrations in the Baltic Proper were slightly above normal for the season at most stations, in the Kattegat concentrations were normal and in the Skagerrak concentrations were normal or below normal for the season at sea. At Släggö the concentrations were above normal for the season.