Cruise report from R/V Aranda week 42, 2018

Type: Report
Author: Örjan Bäck


Initial problems with our CTD caused some delays since a thorough troubleshooting had to be performed. The problem turned out to be the computer and probably a malfunctioning serial port. The computer could temporarily be replaced until we reached Lysekil, there a permanent replacement computer was installed. The delay forced us to skip the second visit at Anholt E. Despite the initial problems we managed to get CTD profiles from all visited stations.

Oxygen concentrations close to zero were observed at many places in the deep water in the Baltic Proper. Anoxic conditions, when hydrogen sulphide forms, were found in the Western Gotland Basin from 60 metres depth. In the Eastern Gotland Basin from around 80 metres and at Hanöbukten closest to the bottom, at 80 metre there was no hydrogen sulphide but the oxygen concentration was very low, <0.1 ml/l. At BCS III-10 in the southeast no hydrogen sulphide was found but the oxygen concentration was <0.1 ml/l at the bottom. Also in the Bornholm Basin very low concentrations of oxygen were found at 80 metres, almost zero, then somewhat higher at the bottom. Oxygen concentrations in the Arkona Basin were lowest at the bottom with 3.41 ml/l.

Nutrient concentrations in the surface layer were at normal low levels for the season, higher values were found below the halocline which is normal. Silicate concentrations in the surface layer in the Baltic Proper continued to be somewhat higher than normal, however not as high as earlier this year or last year.

Surface water temperatures in the entire survey area were normal for the season, on the west coast around 13 °C and in the Baltic Proper between 11-14 °C, warmest in the southern parts. Somewhat colder water, 8-9 °C, were found in the north at BY32 and at the coastal station REF M1V1. Salinity in the surface layer was somewhat higher than normal at several stations in all areas.