Tallinn University of Technology

The initial data of the study, which started at the beginning of October, indicates that the oxygen deficient zone in the Gulf of Finland has extended eastward, but outside of the dead zone the benthic fauna is rich.

The Estonian marine researchers started marine expedition onboard the Tallinn University of Technology’s (TalTech) research vessel “Salme” from the Gulf of Finland to the Bornholm Basin on the 5th of October. The aim was to analyse the oxygen level of the Baltic Sea and the locations of so called dead zones. So far, a very preliminary analysis of the measurements in the Gulf of Finland has been completed.

Participants in the research cruise were researchers from TalTech, University of Tartu and Tallinn University. The Estonian University of Life Sciences provided additional measurement equipment. The study was conducted in the period, when the oxygen level in the Baltic Sea is at the lowest and geographically most extensive.

The marine researcher Urmas Raudsepp from TalTech commented the initial results as follows: “Hypoxic area has spread far east into the Gulf of Finland in this autumn. The oxygen deficiency is also accompanied by a lack of benthic fauna. At the edge of the oxygen deficient area, the benthic fauna is relatively rich. It can be confirmed based on the initial data that the oxygen concentration is very low in the areas that are deeper than 80 metres in the Gulf of Finland. We cannot exclude that there might be low oxygen concentration in shallower parts of the sea also. We anticipate that natural conditions should be the reason for the poor oxygen conditions in the Gulf of Finland. This autumn the deep layers of the Gulf of Finland have water with a very high salinity – 20-25% saltier than usual, which should have transported here from the open parts of the Baltic Sea.”

Finnish researchers  published a few years ago a thorough study finding that the dead zone located in the middle of the Baltic Sea, is the largest of its kind in the world.

Professor Raudsepp added: “The current measurements in the central Baltic Sea and further analysis of water samples should show whether the oxygen poor water has been transported to the Gulf of Finland from the open parts of the Baltic Sea or is intensive oxygen consumption taking place within the gulf. It is very important to know, if this oxygen poor area is permanently in the Gulf of Finland or will it recede by the spring. The oxygen poor area in the Baltic Sea is geographically the smallest in the spring.”

Researchers measure the salinity, temperature and oxygen of the Baltic Sea, take water and bottom sediment samples.

The researchers of the TalTech analyse the relationships between the stratification of the water column and oxygen concentrations, as well as the chemical composition of the sediments.

The contribution of the scientists from the University of Tartu is to determine the variability of nutrients in the spatially changing oxygen conditions, as well as to study the species composition and abundance of benthic fauna in the border areas of oxygen deficiency.

The task of the researchers from Tallinn University is to map the ecological community of bacterioplankton in the hypoxic conditions and based on the DNA analysis to determine the phylogenetic composition of bacterioplankton communities and their spatial dynamics.

Joonis hapniku kihistumisest Soome lahes
Dissolved oxygen distribution in the Gulf of Finland on 5-6 October, 2020. The hatched part is a dead zone. The dotted line shows the course of the TalTech research vessel “Salme”.

Additional information:
Professor Urmas Raudsepp, TalTech Institute of Marine Systems, urmas.raudsepp@taltech.ee