Climate Change and Warmer Water Deprives the Baltic Sea of Oxygen

Climate change may just counteract the decline in eutrophication in the Baltic Sea. Scientists have conducted the first comprehensive analysis over time and have found that general climate change has counteracted measures to protect the Baltic.

A natural phenomenon of the Baltic Sea is the lack of oxygen in the deeper layers of water. This stratification of the Baltic Sea water is stable, with fresh saline and oxygen-rich water only reaching its inner regions from the North Sea through the Danish islands. Yet in the second half of the 20^th century, countries bordering the Baltic Sea dumped large amounts of agricultural fertilizers and sewage into the waters. This actually augmented the lack of oxygen.

"Algae were able to proliferate, and as soon as they die and sink to the bottom, microorganisms decompose the biomass and consume a lot of oxygen," said Sinikka Lennartz, lead author of the new study, in a news release. "This resulted in large oxygen-free zones at the bottom of the Baltic Sea to be formed."

In the mid-1980s, the countries surrounding the Baltic Sea agreed to improve protections of the sea. Sewage treatment plants were built to filter water, and the use of fertilizers in agriculture declined. The hope was this would restore more oxygen to the lower layers. Yet according to data, this isn't the case.

"The oxygen trend is still down significantly," said Lennartz. "We see more and more events at Boknis Eck when no oxygen is measured below 20 meters depth."

So why are these steps not working? One possible explanation could be due to changes in water temperature due to climate change. In fact, the scientists found that in later summers, the temperature on the seafloor has risen by an average of .4 degrees per decade. This means that there's a more efficient degradation of biomass and more consumption of oxygen.

The findings reveal that it's important to continue steps to reduce waste. With increasing temperatures, it's more important than ever to develop policies to protect this region.

The findings are published in the journal Biogeosciences.

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).