Cruise report from R/V Svea week 49-50, 2019

Type: Report
Author: Martin Hansson


Surface water temperature had dropped further since last month. The warmest surface water was found in the Skagerrak and the Baltic Proper Sea with 8°C and coldest water was found in the Gulf of Bothnia with around 2 °C. The levels of nutrients in the surface water (0-10 m) had generally increased since the last measurement. In Skagerrak and Kattegat, the concentration of phosphate and inorganic nitrogen was normal for the season, while the silicate content was lower than normal. In the Baltic Proper, the levels of phosphate were normal but for inorganic nitrogen both levels were higher and lower than normal. Silicate levels were above normal at most stations in the Baltic Proper. In the Gulf of Bothnia the levels of inorganic nitrogen were lower than normal and in the Bothnian Sea normal levels were measured. The concentration of phosphate was elevated throughout the area studied, while the silicate content was normal in the Gulf of Bothnia and above normal in the Bothnian Sea.

In the Arkona basin no oxygen deficiency was measured in the bottom water. Here the oxygen situation was good as a result of an ongoing inflow. In the Hanö Bight and in the Bornholm Basin, oxygen deficiency (hypoxia) were found from 60-70 meters and closer to the bottom, from 70-80 meters depth, completely oxygen-free conditions (anoxia) were observed. In the Eastern Gotland Basin, hypoxia were found at 70 meters depth with anoxia just below. However, at about 100-125 meters depth, low levels of oxygen were found and from 150 meters depth it was completely oxygen free again. The oxygen found here is likely to stem from inflows that occurred earlier this year and that was stored in at intermediate depths. In the Northern and Western Gotland Basin, there was a lack of oxygen at 60 - 70 meters and completely oxygen free from 70 - 90 meters. In the Gulf of Bothnia no oxygen deficiency was measured, but the levels of oxygen in the deep water were in some places lower than normal.