Oxygen depletion in the Baltic Sea is 10 times worse than a century ago

Space Daily via SPX: After several years of discussions, researchers from Aarhus University (Denmark), Lund University (Sweden) and Stockholm University (Sweden) have determined that nutrients from the land are the main cause of widespread areas of oxygen depletion. The results were published on 31 March in the prestigious American journal Proceedings of the National Academy of Sciences.

The deepest areas of the Baltic Sea have always had a low oxygen content. The inflow of fresh water is actually limited by low thresholds at the entrance to the Baltic Sea. At the same time, there is a relatively fresh layer above the denser and saltier water in the deep layer of the sea. This results in an effective stratification of the water column, which prevents the mixing of water masses necessary to transfer oxygen to the water at the bottom.

During the last century, the areas of oxygen depletion have increased drastically from approximately 5,000 km2 in around 1900 to the present day, where they extend to 60,000 km2 - or about one and a half times the total area of Denmark.

"We analysed data for the water temperature, oxygen content and salinity stretching back for 115 years. On the basis of this analysis, we can determine that the many nutrients from the land are the main cause of the widespread oxygen depletion," says Professor Jacob Carstensen, Department of Bioscience, Aarhus University.

...During the last twenty years, climate change has also played a role in the poor oxygen situation. Warmer conditions reduce the solubility of oxygen from the atmosphere and increase oxygen consumption because the biological respiration processes are boosted.

"The water temperature has risen and will continue to rise in the years ahead. It's therefore extra important that all the countries surrounding the Baltic Sea are committed to the Baltic Sea action plan they joined, and that they comply with the necessary efforts to reduce the release of nutrients into the Baltic," emphasises Professor Carstensen, who is also director of the Baltic Nest Institute in Denmark....

Belarus and Baltic countries on Carta Marina