Cruise report from R/V Aranda week 34, 2016

Type: Report
Author: Örjan Bäck


The temperature in the surface water was normal for the season and varied between 16 and 18 °C. The salinity in the surface waters on the west coast was normal, in the southwestern parts of the Baltic Proper it was slightly above normal and somewhat below normal in the northern parts of the Eastern Gotland Basin. There were salinity stratifications at around 10 to 20 meters in the Kattegat and near the coast in the Skagerrak, the thermocline varied in strength and depth but was usually found between 30 to 60 meters.
Nutrients, in the form of phosphate and inorganic nitrogen (nitrite, nitrate and ammonia) were depleted in the surface waters in the entire survey area. Not until below the halocline the nutrient concentrations increased. The concentration of silicate at the surface was normal or just above normal at a few stations. Acute hypoxia (dissolved O2 < 2 ml/l) was found from around 70 meters in the entire Baltic Proper. Hydrogen sulfide was only found close to the bottom, at 150 and 175 meters depth, at BY20 Fårö deep and at the bottom, 235 meters, at BY15 Gotland deep, and also from 80 meters and below in the Western Gotland Basin.