Cruise report from R/V Aranda week 11, 2019

Type: Report
Author: Örjan Bäck


The entire water column was generally well mixed in the Skagerrak area, which resulted in higher than normal salinity and temperature in the surface waters. At Å17 a weak stratification could be seen at around 30 meters, with somewhat colder and less salty water in the surface layer. The nutrient concentrations were, similar to temperature and salinity, well distributed over the entire water column. Compared to normal this meant lower or much lower concentrations in the deep waters. Also in the Kattegat nutrient concentrations below normal could be seen below the halocline.

In the Baltic Proper, both in the Eastern and Western Gotland Basin, temperature and salinity values higher than normal were found below the stratification.

No hypoxia (<2 ml O2/l) was found in the Arkona Basin, however in the Bight of Hanö and in the Bornholm Basin hypoxia appeared from 70 meters and below, no samples with hydrogen sulphide (formed in anoxic conditions) were found in this area. Also further east, in the Eastern and Western Gotland Basin, hypoxia started from 70 meters depth. Hydrogen sulphide was first observed at BY10 closest to the bottom at 144 meters depth and at BY15 from 150 meters and below. Even though no hydrogen sulphide was found until around 150 meters the oxygen concentrations between 80 and 150 meters were very low, close to 0 ml/l. Further north at BY20, and west into the Western Gotland Basin at BY32 and BY38, hydrogen sulphide was observed from 80 meters depth and below.