Ocean pH value decreasing

A research project into ocean acidification has increased knowledge about conditions in the Baltic Sea and Kattegat-Skagerrak. When the pH value falls, the whole marine ecosystem is affected. A newly developed measurement technique provides information about natural variations in the oceans, which results in improved environmental monitoring.

Since 1850 the pH value of the world’s oceans has fallen by 0.1 units, and it is expected to fall a further 0.2 units or so by the year 2100. The pH value is affected by the fact that one-third of the world’s carbon dioxide emissions into the atmosphere are absorbed by the oceans. This is positive because the increase in carbon dioxide levels in the atmosphere is slowed – the greenhouse effect is reduced somewhat. At the same time, however, the oceans are acidified when they absorb carbon dioxide.

Consequences for the marine ecosystem

The change in ocean pH value affects the whole marine ecosystem. Many marine plants and animals, such as corals, mussels, molluscs and crustaceans, form skeletons from chalk. When the pH value falls, forming chalk shells and skeletons requires more energy.

Growing mussels. Photo Pia Norling.
Foto Pia Norling

“Animals and plants with chalk shells and skeletons play an important role both in the marine food web and by forming habitats such as coral reefs. It is not, however, only organisms with chalk shells or skeletons that are affected. A decreasing pH value will probably lead to a sharp decrease in biological diversity,” says Bengt Karlson, marine biologist and scientist at SMHI.

Researchers at Gothenburg University have conducted experiments with animals and plants from the Baltic Sea and Kattegat-Skagerrak. The results show, for example, that larval stages can be particularly sensitive to acidification. In addition to impact on the marine ecosystem, some fundamental processes that occur in many organisms are affected, such as photosynthesis.

New measurement technique and continuous measurements

In the research project entitled Ocean acidification – the state of the Baltic Sea and the Kattegat-Skagerrak, SMHI and Gothenburg University have examined the present conditions in the Baltic and Kattegat-Skagerrak. The project has also developed a new high-precision chemical measurement technique.

In addition to the standard monthly measurements using research vessels, continuous measurements are now also carried out using a cargo ship which sails a route from Gothenburg to northern Finland and back every week.

“Continuous and more accurate measurement provides us with information about natural variations in the oceans. Along with the monthly measurements, this provides us with a basis that leads to improved environmental monitoring,” says Karlson.

About the project

The three-year research project is funded by the Swedish Environmental Protection Agency/the Swedish Agency for Marine and Water Management and has been conducted by SMHI and Gothenburg University. Thanks to a collaboration with Transatlantic AB, continuous measurements can be carried out with the cargo ship TransPaper.

Measurements with FerryBox on the TransPaper

SMHI runs a FerryBox system on the TransPaper which sails the Gothenburg-Kemi-Oulu-Lübeck-Gothenburg route. This makes it possible to take measurements close to the surface in the Gulf of Bothnia, the Baltic Sea proper, the Belt Sea and the Kattegat twice a week. Automatic measurements are taken every 20 seconds and water samples every other week. The parameters measured include the amount of plankton, salt levels, temperature, oxygen content, the water’s transparency and brownness, and pH. Carbon dioxide is measured in both the air and water. Insolation and temperature are also measured in the air. Water samples are taken for plankton analysis and other laboratory analyses.

Fartyget TransPaper som trafikerar haven nonstop.