Cruise report from M/V Aura week 21-22, 2018

Type: Report
Author: Johan Kronsell


The warm and sunny weather in May, in combination with calm winds, had warmed the surface water, and the surface water temperature was above normal at all visited stations. High phytoplankton activity was found mainly at the stations in the Baltic Proper, indicating ongoing spring bloom. Large peaks of fluorescence were found at 10-20 meters depth.

In large areas of the Baltic Proper, oxygen concentration in the deep water was close to zero. Anoxic conditions, when hydrogen sulfide can form, were found in the Bornholm Basin and the Bay of Gdansk at about 90 meters depth, in Bight of Hanö at 77 meters, and in Western and Eastern Gotland Basin at about 70 and 140 meters depth respectively. Acute hypoxia (oxygen < 2ml/l) was found from about 70 meters depth at the stations in the Baltic Proper, but also at the bottom at about 45 meters depth in one of the stations in the Arkona Basin.

Dissolved inorganic nitrogen was below detection level at the entire survey area, which is normal for the season. Concentration of phosphate was below normal in the Eastern, Western and Northern Gotland Basin. Silicate concentration in the surface was above normal levels in the southern part of the Eastern and Western Gotland Basin and in the Bay of Gdansk. The other investigated areas showed values normal for the season.