CPH Post

Sci/Tech

Baltic Sea bed dying fast, claims study

New Aarhus study shows unprecedented extent of oxygen depletion in the Baltic Sea


Soon only bacteria will be able to survive here (Photo: Wiki Commons) N

April 3, 2014
07:00

by Alina Shron


Oxygen depletion in the Baltic Sea has increased more than tenfold in the past century, according to a new Aarhus University study published on 31 March in the prestigious American journal Proceedings of the National Academy of Sciences.

The depleted areas have grown in size from approximately 5,000 sq km in around 1900 to 60,000 sq km – or one and a half times the total area of Denmark – today.

While the deepest parts of the Baltic Sea have always been low on oxygen, the drastic changes cited in the study are believed to be of man-made origin.

“On the basis of this analysis, we can determine that the many nutrients from the land (i.e fertilizer) are the main cause of the widespread oxygen depletion," explained Professor Jacob Carstensen from the university's Department of Bioscience to Science News Site EurekAlert.

Climate change a factor
Over the last 20 years, claimed the report, climate change has also played a role in the poor oxygen situation. The water temperature in the Baltic Sea has increased by two degrees. Warmer conditions both reduce the solubility of oxygen from the atmosphere and increase oxygen consumption.

Carstensen, who is also director of the Baltic Nest Institute in Denmark, stressed that “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.”

Oxygen depletion takes place when the oxygen uptake at the bottom exceeds the amount of oxygen brought to the deeper water layers through currents and mixing by wind.

Decades of recovery necessary
The depletion of oxygen on the seabed has adverse consequences for the entire ecosystem. It makes the survival of any life form but bacteria impossible on the seabed and makes it more likely that bacterial processes can kill fish higher up in the water.

A dead seabed can be revived if the oxygen conditions improve, but it takes decades before the fauna returns.




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