Mediaeval Baltic Sea severely affected by oxygen depletion

 15 Feb 2011

Go back a thousand years, and you would find the sea surface temperature of the Baltic Sea slightly warmer and the oxygen depletion much wider spread than it is today. These are some of the preliminary findings of the international INFLOW research project within BONUS, the joint Baltic Sea Research and Development Programme. The Academy of Finland is the Finnish funding agency participating in BONUS.

By examining marine sediments of the Baltic Sea and using a modelling approach, the INFLOW researchers will gain new knowledge of the state of the sea through different centuries. This new information sheds light on sea surface temperature, sea ice cover and eutrophication levels at different times. Led by the Geological Survey of Finland and funded by the Academy of Finland, the INFLOW research project will produce model simulations to provide selected scenarios of the impact of natural and human-induced climate change on the Baltic Sea ecosystem.

“The extent of oxygen depletion was already a big problem in the Baltic Sea a thousand years ago, despite minimum interference from human activities. Then the climate cooled and the rate of oxygen depletion decreased. However, the climate got warmer again in the 20th century, which in turn increased oxygen depletion,” says INFLOW Coordinator Aarno Kotilainen, Research Professor at the Geological Survey of Finland.

According to Kotilainen, the findings translate into a discouraging forecast for the future, as the external load on the Baltic Sea continues to increase in the wake of growing human activity. Climate change, rapid population growth and increased use of marine and coastal areas are, in fact, real threats to marine environments the world over.

“Some estimates suggest that climate change in the Baltic Sea area causes sea surface temperatures to rise, increases winds and shortens the ice-cover season. Changes in the hydrography and biogeochemical processes of the Baltic Sea may influence the entire ecosystem. The complex cause-and-effect relationships make it very difficult to assess the scope and trends of these impacts,” says Kotilainen.

The INFLOW project is creating a model for natural variability in marine ecosystems, which will help in understanding long-term changes in the Baltic Sea and the contributing factors. The model will also allow for better forecasting of future variations. This knowledge is crucial in drafting plans for the sustainable use of marine areas and in preparing for the impacts of climate change.

INFLOW is one of 16 BONUS+ projects that generate new knowledge in support of decision-making in the Baltic Sea region. The project includes leading researchers from seven Baltic Sea countries: Finland, Sweden, Norway, Denmark, Germany, Poland and Russia. This ensures the best possible knowledge base in Baltic Sea sediments and modelling.

The multidisciplinary BONUS programme is funded by the EU and research funding agencies from eight EU Member States: Finland, Sweden, Denmark, Germany, Poland, Latvia, Lithuania and Estonia. Russia participates through individual projects. The Academy of Finland is the participating Finnish funding agency.

More information:

  • Research Professor Aarno Kotilainen, Geological Survey of Finland (GTK), tel. +358 20 550 2576, firstname.lastname(at)
  • Communications Manager Maija Sirola, BONUS Secretariat, tel. +358 40 352 0076, firstname.lastname(at)

Academy of Finland Communications
Riitta Tirronen
Communications Manager
tel. +358 9 7748 8369, +358 40 828 1724



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