Cruise report from R/V Svea vecka 11-12, 2020

Type: Report
Author: Martin Hansson


The surface water temperature was well above normal and ranged between 4 - 6°C which is about 2-3°C above normal for the season. The deep waters in the Baltic Proper were also warmer than normal. In the Baltic Proper, the salinity was higher than usual. The concentrations of dissolved inorganic nitrogen were elevated in parts of the Skagerrak as well as in the Western Gotland Basin. Phosphate and silicate concentrations were elevated in large parts of the Baltic Proper.

The oxygen situation in the Arkona Basin was good with concentrations above 6 ml/l. In Hanö Bight, the Bornholm Basin and in the southeastern Baltic Proper oxygen levels in the bottom water had decreased since the last measurement in February and was now just over 2 ml/l, which is the limit for acute oxygen deficiency. Acute oxygen deficiency was observed from 55-70 meters depth in these areas. In the southern and central parts of the Eastern Gotland Basin, acute oxygen deficiency was noted from 55-65 meters, in the northern parts from 70 meters depth. In the Western Gotland Basin a little deeper, from 70-80 meters depth. Anoxic waters, oxygen-free conditions where toxic hydrogen sulphide is formed, were found in the Eastern Gotland Basin at depths exceeding 125 meters. In the Western Gotland Basin from 90 meters depth.