Cruise report from R/V Aranda week 7-8, 2019

Type: Report
Author: Lena Viktorsson


The February cruise, which is part of the Swedish national marine monitoring program, covered the Skagerrak, the Kattegat, the Sound and the Baltic Proper. In the Baltic Proper winter mapping of nutrients was performed.

In the northern and westerns parts of the Baltic Proper there was hydrogen sulfide from 80 m depth to the bottom. In the Eastern Gotland Basin from BY15 and to the south there were traces of a smaller inflow with warmer water than the ambient water and low concentrations of oxygen (<0.5 ml/l) at around 100-115 m. From the station BY9 Klaipeda and south of this there was no hydrogen sulphide. At BCS III-10 in the south-east there was no hydrogen sulfide but the oxygen was below the reporting limit (<0.1ml/l). In the Bornholm basin and Hanö bay it was oxic down to the bottom but with concentrations <2ml/l from 80 m depth. There was no oxygen deficiency in the Arkona basin where the oxygen concentration was >4ml/l in the whole profile.

In Kattegat the nutrient concentrations were unusually low, as they were already in January. The concentrations were not as low in Skagerrak, but in both sea areas the phytoplankton production seemed to have started, which is earlier than normal. The winter mapping of nutrients in the Baltic Proper showed that the concentration of silica in the surface water (0-10 m) was above normal in almost the whole sea area. The concentrations of dissolved inorganic nitrogen and phosphorus were lower than normal in the southern parts of the Baltic Proper, similarly to the Kattegat.

The sea surface water temperature was between 2-5℃, coldest in the northern parts of the Baltic Proper and warmest in the Skagerrak, The sea surface temperature was slightly above normal at the stations in the Eastern Gotland Basin, the Sound and at P2 in Skagerrak, The sea surface salinity was slightly higher than normal in parts of the Eastern Gotland Basin, the Sound and the Skagerrak. In the Skagerrak and the Kattegat the halocline was at around 10-20 m depth with colder winter water on the surface. In the Baltic Proper the halocline was at 60 m, as normal.