Cruise report from R/V Svea week 6-7, 2024

Type: Report
Author: Karin Wesslander


During the expedition, as part of the Swedish pelagic monitoring program, the Skagerrak, the Kattegat, the Sound and the Baltic Proper were visited. In the Baltic Proper extra stations were visited for the mapping of winter nutrients.

The temperature in the surface water was normal to slightly above normal and ranged from 2–3 °C in the Baltic Sea to 3–6 °C in the Skagerrak and Kattegat.

In Skagerrak, the concentration of dissolved inorganic nutrients had increased in the surface water and were normal for the month. Similarly, in Kattegat, nutrient levels were normal, but the concentration of DIN (dissolved inorganic nitrogen) had increased since January, while silicate had decreased and phosphate levels remained roughly the same. In the Baltic Proper, the concentration of nutrients had increased at most stations since January. The concentration of DIN was normal, and silicate was above normal throughout the Baltic Proper. The concentration of phosphate was normal in the Arkona, Bornholm, and Western Gotland Basins and above normal in the Eastern Gotland Basin and northern Baltic Proper.

The oxygen situation was good at all stations in Skagerrak, Kattegat, and the Sound; no oxygen deficiency was noted.

In the Arkona Basin, the oxygen situation was good in the bottom water, and the oxygen concentration had increased slightly since January. The inflow that occurred at the end of December 2023 could now be seen on its way through the Bornholm Basin; at stations BY4 and Hanö Bay, the oxygen concentration had decreased since January, but at BY5, there was instead a significant increase in oxygen in the bottom water compared to January. At BY5, the oxygen concentration just above the bottom was just below the oxygen deficiency limit (<4 ml/l), but above that, there was still a layer of acute oxygen deficiency (<2 ml/l). In the Eastern Gotland Basin there were anoxic conditions, hydrogen sulphide was measured from 70 m, with acute oxygen deficiency from 60 m. In the northern Baltic Proper, there were anoxic conditions from 90 m and acute oxygen deficiency from 80 m. In the Western Gotland Basin, the depth levels for anoxic conditions and acute oxygen deficiency varied from 125 and 90 m at BY31 to 70 and 60 m at BY38, respectively.

SMHI’s next regular expedition with R/V Svea is scheduled for March 8th to 13th, starting in Kalmar and ending in Lysekil.