Cruise report from R/V Svea week 15-16, 2024

Type: Report
Author: Örjan Bäck


The Kattegat, Öresund, the Baltic Proper and a coastal station in Skagerrak were visited during this cruise, which is part of the Swedish environmental monitoring program area coast and sea.

The surface water temperature was normal for the month, around 7 °C on the west coast and varied between 3 to 5 °C in the Baltic Sea. In the Southern Baltic Sea and Öresund, the salinity in the surface water was slightly below the monthly average, while in the Northern Baltic Sea, it was slightly above average.

The concentrations of nutrients were low both in the Kattegat and the Southern Baltic Sea but within the normal range. Inorganic nitrogen was largely depleted after the spring bloom. In the Eastern and Western Gotland Basins, the levels of both inorganic nitrogen and phosphorus were higher than normal near the surface. Below the halocline, values were also higher than normal at several stations, especially near the bottom. Silicate levels were somewhat higher than normal throughout the Baltic Sea.

The oxygen situation in the bottom water was good (>4 ml/l) at all stations in the Skagerrak, the Kattegat, Öresund and the Arkona Basin west of Bornholm, no oxygen deficiency was noted. In Hanö Bay and the Bornholm Basin east of Bornholm, the oxygen levels in the bottom water varied between 2 to 3 ml/l, just above the threshold for acute oxygen deficiency (<2 ml/l). In the Eastern and Western Gotland Basins, hydrogen sulphide was noted from about 80 metres depth, and the concentration increased towards the bottom. At all stations with hydrogen sulphide in the deep water, concentrations were higher than the monthly average for the reference period and have been so at these stations for the past few years.