Cruise report from R/V Svea week 37-38, 2023

Type: Report
Author: Örjan Bäck


The Skagerrak, the Kattegat, Öresund and the Baltic Proper were visited during this cruise, which is part of the national marine monitoring programme of Sweden.

The warm weather in September had caused the water temperature in the surface water to rise since August in all areas except in the Western Gotland Basin, where the temperature had dropped by around 1 degree. The temperature varied between 16.5 to 18.5 °C, in the Western Gotland basin from 14 to 16 °C.

The nutrient concentrations in the surface water were generally low in all areas, which is normal for the season, slightly higher phosphate levels occurred in the Western Gotland basin. In the deep water there were higher levels but within the normal range, however, higher concentrations of nutrients were observed in the deep water in the Eastern Gotland basin, also higher than normal levels of phosphate were found at the bottom in the southern Kattegat and in Öresund.

In the Arkona Basin, west of Bornholm, there was acute oxygen deficiency (O2 < 2 ml/l) closest to the bottom with concentrations between 0 and 1 ml/l, likewise the oxygen concentration at the bottom in Hanö Bay was close to 0 ml/l. In the Bornholm basin, east of Bornholm, it was completely oxygen-free at the bottom and instead concentrations of hydrogen sulphide were measured. In the Gotland basins, the oxygen ran out at a depth of around 70 to 80 metres. At the majority of stations in the Gotland basins, there are now record high levels of hydrogen sulphide closest to the bottom.

SMHI's next cruise with R/V Svea is planned to start the 19th of October, starting in Kalmar and ending in Lysekil.