The Baltic Sea emits more carbon dioxide than it can bind¹. Local variations have increased the exposure of the Bay of Bothnia. These are the results from a study of how carbon dioxide flows between the water of the Baltic Sea and the atmosphere, carried out by scientists at the University of Gothenburg, Sweden. "The capacity of the Baltic Sea to absorb carbon dioxide without major changes to the acidity² of the water has changed in recent centuries. In the Bay of Bothnia, the ability to resist change has fallen, while it has increased in the south-eastern parts of the Baltic Sea," says Karin Wesslander of the Department of Earth Sciences at the University of Gothenburg.

The concentration of carbon dioxide in the atmosphere is rising steadily³ as a result of human activities, but global climate models remain inaccurate⁴. The coastal⁵ seas are rarely included in large-scale climate models. Karin Wesslander has investigated the carbon dioxide system of the surface water of the Baltic Sea, in order to increase understanding of how the concentration of carbon dioxide affects seas.

Carbon dioxide is an important component⁶ of photosynthesis⁷（光合作用） , which converts the energy from sunlight, and it is phytoplankton（浮游植物） that carry out photosynthesis in the seas. The carbon dioxide in the sea is consumed during the algal blooms that take place during the spring and summer.

This means that the fraction of carbon dioxide in the water is lower than it is in the atmosphere, and carbon dioxide flows into the sea. The sea is thus a sink for atmospheric⁹ carbon dioxide. When the plankton⁸（浮游生物） subsequently die, they are broken down and the carbon dioxide reappears in the water. The windy weather that occurs during the autumn and winter causes water mixing, and the carbon dioxide returns to the surface. This is the reason that the sea is most often a source of carbon dioxide during these seasons.