Tallinn University of Technology

On 5 October, Estonian marine researchers will head to the expedition on TalTech’s exploration vessel “Salme” to analyse oxygen concentrations in the Baltic Sea and the spread of the dead zones from the Gulf of Finland to Denmark Strait, in the season where marine oxygen levels are the lowest and geographically the most wide-spread.

The expedition is attended by researchers from TalTech and the universities of Tartu and Tallinn, and the Estonian University of Life Sciences will provide them with the measuring instruments needed.

According to TalTech marine researcher Urmas Raudsepp, the purpose of the research is to identify the potential size of the area where the oxygen deficiency may spread in the Baltic Sea and what this would entail for the marine ecosystem.

Professor Raudsepp of the Department of Marine Systems said: “Dead zones are low-oxygen areas in the sea, which have severe effects on the survivability of living organisms in the sea. Previous studies have shown that dead zones take up 60,000–80,000 square kilometres of the Baltic Sea. Very broadly speaking, it can be said that in the Baltic Sea, areas deeper than 80 metres are dead zones. Of course, this does not concern the Gulf of Bothnia. At the same time, the size of the geographic area where the oxygen deficiency may spread to is not clear. High stratification 60–80 metres deep prevents oxygen access from the upper strata of the water.”

Raudsepp added: “Also, oxygen starvation is further contributed to by the bacteria in deeper layers of water, which, by decomposing the organic matter, use up the already little oxygen there is in the water. Out hypothesis is that the area of year-round dead zones in the Baltic Sea is not increasing, but areas of seasonal and episodic hypoxia may increase. This research will give important input for decision-makers by showing which measures could prevent the further spreading of the dead zones in the Baltic Sea and what, regrettably, only depends on natural factors.”

The researchers are planning to measure salinity, temperature and oxygen levels, take water samples and analyse the spread of marine flora and fauna and richness of species, based on the bottom sediment.

They intend to focus on the part of the Baltic Sea deeper than 60 metres, with constant and seasonal low-oxygen areas.

TalTech researchers will be analysing the links between water stratification and dead zones, and the chemical composition of sediments.

Researchers from the University of Tartu plan to identify the variation of nutrients due to spatial changes in oxygen conditions and answer the question of whether there is any marine biota and what it is like in the border zones of oxygen deficiency.

Researchers from Tallinn University aim to map the bacterioplankton communities in constantly oxygen-deprived conditions and, based on the DNA analysis, establish the phylogenetic composition of these bacterioplankton communities, and the spatial dynamics of these communities.

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