Cruise report from R/V Aranda week 24, 2019

Type: Report
Author: Anna-Kerstin Thell


The cruise in June, which is part of the Swedish national marine monitoring program, covered the Skagerrak, the Kattegat, the Sound and the Baltic Proper. The sea surface temperatures and salinities were normal in all sea areas. The spring bloom had consumed the majority of the nutrients in the surface water but elevated amounts of silicate were still present in the Baltic Proper. CTD measurements showed high chlorophyll fluorescence in the whole area between 5 and 25 meters with peaks in the Baltic Proper at about 20 meters depth. Acute hypoxia (< 2ml/l) were noted from 65 - 75 meters depth in the whole area. Oxygen was found intermediate at BY15 between 105 and 145 meters depth and at BY10 between 75 and 125 meters depth. Hydrogen sulphide, which is formed during oxygen free conditions, was found in the Eastern and Western Gotland Basins. In the Eastern Gotland Basin, the water was totally depleted from oxygen from 145 meters at the Gotland depth (BY15) and from 125 meters in the Fårödjupet (BY20) and BY10 and down to the bottom. In the Western Gotland Basin, oxygenwas absent from 80 meters and downwards and the levels of hydrogen sulphide in the deep water were much higher than normal.

Next regular cruise is scheduled to 14th – 21th of July.