The water in the Baltic Sea has become warmer

Measurements at the Finnish research station Tvärminne show that the temperature has increased by two degrees in the coastal sea since the 1990s.

This is little more than the average temperature increase in what the researchers call the actual Baltic Sea, an area between Åland and the Sound. There, there has been an increase of about 1.5 degrees in surface water since the 1990s.

Temperature increases occur faster in the Baltic Sea than in the world oceans.

- The Baltic Sea is shallow. The average depth is 60 meters compared to the world oceans 3 kilometers. It is like a shallow bathtub and heats up much faster, says Alf Norkko, one of the authors of the study.

The measurements from Tvärminne show that during the heat wave last year it was over 20 degrees warm as far as 30 meters down into the sea, something that has never been measured before.

- It's a snapshot, says Alf Norkko, but it says something about what happens when we get extreme heat waves.

During the summer of 2018, greenhouse gas levels in the Baltic Sea were also measured.

- It has not been possible to measure gases in water very well in the past, but with our new measurement method we see that the methane sources emit more gases when it gets warmer.

This indicates that the greenhouse gases methane and carbon dioxide stored in the seabed are released as a result of the temperature increases, in the same way that they are released in tundra that melts or ants that are heated.

- We have over-fertilized coastal areas in both Sweden and Finland. Then a lot of organic material is collected on the bottoms. Hot temperatures release exhaust gases from this material.

When these gases reach the sea surface, they in turn contribute further to the warming in the atmosphere.

The study from Tvärminne is published in Frontiers in Marine Science.

Read more about the Baltic Sea temperature here.