Cruise report from R/V Aranda week 30, 2015

Type: Report
Author: Martin Hansson


The water temperature in the surface layer was essentially normal or somewhat lower than normal for the season. In the southern and southeastern Baltic Proper very high concentrations of phosphate and silicate were measured. The large inflow that occurred in December 2014 had now reached the northern parts of the eastern Gotland basin, but the oxygen levels in the inflowing water had now declined to below 2 ml/l. In the northern and western Gotland basin and in the western part of the Gulf of Finland the oxygen situation remains severe as completely oxygen free conditions are found at depths exceeding 70-90 metres. Acute hypoxia was found from 55 metres in the western Gotland basin. In the bottom water in the Arkona and Bornholm basins, and in the Hanö Bight, oxygen levels had declined compared to the previous sampling in June and acute hypoxia was experienced. Phytoplankton analysis showed relatively large amounts of cyanobacteria in the Baltic Proper, which could also be clearly seen in the surface water in the northern parts, as well as in the Bornholm basin. Surface accumulations were only observed in a small area in the eastern Arkona Basin. For a more detailed analysis of the phytoplankton situation, please see the separate report.