Cruise report from R/V Aranda week 19-20, 2019

Type: Report
Author: Martin Hansson


The sea surface temperature and salinity was normal in all sea areas, except the surface salinity that was above normal in parts of the Skagerrak, in the Eastern Gotland Basin and in the Hanö Bight. The deep water in parts of the Baltic Proper showed temperature and salinity above or high above normal values. The spring bloom had consumed the majority of the nutrients in the surface water but elevated amounts of silicate were still present in the Skagerrak, the Kattegat and in large parts of the Baltic Proper. Some plankton activity occurred in both the Skagerrak and the Kattegat as distinct fluorescence maxima, but in the Baltic Proper the plankton activity was more evenly distributed in the surface layer down to 20 meters depth.

In the Western Gotland Basin unusual high concentrations of hydrogen sulphide, which is formed during oxygen free conditions, was found in the deep water. Oxygen free conditions, with hydrogen sulphide present, were also found in the Eastern Gotland Basin from 130 meters depth and in the Western and Northern Gotland Basins and in the Gulf of Finland from depth exceeding 80-90 meters. In the whole Baltic Proper and the Gulf of Finland oxygen deficiency (oxygen < 2ml/l) was found from 65 - 75 meters depth.