Summary
During the expedition, which is part of the Swedish pelagic monitoring program, the Skagerrak, the Kattegat, the Sound, the Baltic Proper and the Gulf of Bothnia were visited.
During the expedition, which is part of Sweden's pelagic monitoring program, the Skagerrak, Kattegat, Öresund, Baltic Proper, and the Gulf of Bothnia were visited. In the Gulf of Bothnia, SMHI and the Umeå Marine Research Center (UMF) jointly conducted a mapping of, among other things, nutrients.
Surface water cooling continued in December and was within the normal range at most stations in all marine areas. Surface water temperatures ranged between 6-7 °C in the Skagerrak, 7-8 °C in the Baltic Proper, and 3-5 °C in the Gulf of Bothnia.
Nutrient concentrations increased in both the Kattegat and the Baltic Proper compared to November. At some stations, phosphate and silicate concentrations exceeded normal levels, while dissolved inorganic nitrogen concentrations were below normal. However, at most stations, concentrations were within normal ranges.
In the Gulf of Bothnia, a north-south gradient in nutrient concentrations was observed. Silicate and dissolved inorganic nitrogen decreased towards the south, while phosphate concentrations increased. Additionally, there was an east-west gradient, where the concentration of dissolved inorganic nitrogen was notably lower at stations in the eastern parts. Phosphate concentrations were above normal in the Bothnian Sea but not in the Bothnian Bay. Dissolved inorganic nitrogen concentrations were mostly within the normal range.
Oxygen concentrations in bottom waters were normal in the Kattegat (5.0-5.6 ml/l) and Öresund (4.1 ml/l). In the Arkona Basin, bottom water oxygen levels were favorable, with concentrations around 5 ml/l. In the Bornholm Basin, acute oxygen deficiency (<2 ml/l) persisted, while Hanö Bay experienced an inflow of new water that increased oxygen concentrations to just above 2 ml/l in bottom waters. Increased oxygen concentrations were also observed around 60-70 meters in the Bornholm Basin. At station BY39, oxygen concentrations were 2.0 ml/l, indicating acute oxygen deficiency at a depth of only 50 meters. In the rest of the Baltivc Proper, oxygen conditions remained unchanged since November. In the Eastern Gotland Basin, hydrogen sulfide was detected from 90 meters and acute oxygen deficiency from 75 meters. In the Western Gotland Basin, hydrogen sulfide was detected from 60-80 meters, with acute oxygen deficiency from 55-65 meters.
The next expedition with R/V Svea is scheduled to start on 9 January in Gothenburg, during which nutrient mapping in the Kattegat will also be conducted.