Cruise report from R/V Aranda week 42, 2015

Type: Report
Author: Karin Wesslander


The surface water in Skagerrak and Kattegat was somewhat cooler, around 11°C, than the surface water in the Baltic Proper where there was about 13°C. Inorganic nitrogen (NO2+NO3) in surface waters were close to the detection limit in all regions. The concentrations of phosphate were low throughout the region except in the Southern Baltic, where they were somewhat higher than normal. The effect of the large inflow event in December 2014 could not be seen farther north than the station BY20 in the Eastern Gotland Basin. The inflow event contributed to more oxygen in the Baltic Proper deep water but oxygen levels are now declining and the oxygen concentration in the Gotland Deep had now been reduced to 0.5 ml/l. The concentration of hydrogen sulphide has decreased which probably is an effect of the inflow. In Western- and Northern Gotland Basins the oxygen situation remains severe. In the Western Gotland Basin, completely oxygen-free conditions were found from 80-90 meters while acute hypoxia occurred from 80 meters. The northern part was completely oxygen-free from 70-80 meters and acute hypoxia occurred from 70 meters. Oxygen levels in the bottom water in the Bornholm Basin and Hanö Bight had decreased by a further 0.5 ml/l since the previous survey in September and acute hypoxia was also noted. During the entire expedition an outflow from the Baltic to the Kattegat was ongoing and there was a strong two-layer stratification in the Sound.