press release, 09. May 2018

The Baltic Sea as a Time Machine

A small sea as a model region for the global coastal ocean

Warming, acidification, eutrophication, and the loss of oxygen - these are just a few examples of major changes being observed or expected for the future in coastal zones of oceans around the world. These processes are occurring in the Baltic Sea at a much faster pace than in other regions. At the same time, the Baltic provides useful lessons for how negative trends can be reversed by protective measures. In the international journal Science Advances, an international team of researchers led by the GEOMAR Helmholtz Centre for Ocean Research Kiel and with the participation of UFZ scientists promotes the Baltic Sea as a time machine for coastal areas worldwide.

 Photo: Christoph Kersten, GEOMAR

Photo: Christoph Kersten, GEOMAR

At first glance, the Baltic Sea seems to be rather uninteresting for scientists working on global ocean topics. It is comparatively shallow, has a low salinity and only a very narrow connection to the North Atlantic. This impression is, however, deceiving. In the current issue of the international journal Science Advances, 26 authors from 21 scientific institutions in seven countries appeal to the greater scientific community and policy makers to use the Baltic Sea Region as a model for coming changes in the World Ocean. "This unique sea of brackish water can serve as a kind of time machine that allows us to better estimate future global changes," says Prof. Thorsten Reusch from the GEOMAR Helmholtz Center for Ocean Research Kiel, one of the lead authors of the article.

The scientists argue that changes that are only expected for the future in the global ocean can already be observed in the Baltic today. This is because the small volume of water and slow water exchange with the open ocean, behaves like an amplifier, allowing many processes and interactions to occur at a faster pace.

As examples, the oceans have warmed by an average of 0.5°C over the past 30 years, while in the same period, time-series measurements in the Baltic Sea have recorded warming of around 1.5°C. Likewise, there are large oxygen-free zones in the deep areas of the Baltic Sea, which have increased tenfold over the past century; and the pH - a measure of ocean acidification - of Baltic waters regularly reaches values that are expected in other ocean areas only in the next century.

On the one hand, these extremes are caused by the particular basin topography of the Baltic Sea. On the other hand, intensive use by humans continues to accelerate negative changes. Nine countries border on the Baltic Sea directly and all are highly industrialized, with densely populated coastal regions. Moreover, intensive agriculture in the interior ensures high nutrient runoff, while equally intensive fisheries puts pressure on the pelagic food-web.

Researcher from the Helmholtz Centre for Environmental Research (UFZ) found out that the Baltic Sea is one of the rare examples where successful combination of promoted systematic monitoring, data sharing, science-based management and awareness raising has led to a macro-regional trend reversal of nutrients loads. "The early implementation of cross-border environmental management in the Baltic Sea resulted in a 50% and 70% decrease in nitrogen and phosphorus loads, respectively, from coastal point sources between 1985 and 1995", says Dr. Seifeddine Jomaa who works as hydrologist at the UFZ.

But it’s not all doom and gloom. The Baltic Sea is one of the best-surveyed seas on Earth. Scientific observation and monitoring of physical and biological processes began around 1900. There is a strong tradition in scientific co-operation among many countries surrounding the Baltic, culminating in the implementation of the joint Baltic Sea research and development programme BONUS of the European Union, a dedicated macro-regional research agenda and funding scheme that also enabled the present study. These data provide a sound basis for science-based resource management "on a level accomplished in only a few regions of the world," emphasizes Professor Reusch. 

Among the management success stories: the bordering countries have managed to significantly reduce nutrient inputs since the 1980s, to reverse the decline of large predators, and to curb overfishing. This has been achieved through the binding agreements within the framework of the European Union, but also thanks to the ambitious goals of the Baltic Sea Action Plan (BSAP), which included Russia, even before the end of the Cold War. In fisheries, the protection of capture fisheries, marine mammals and bird populations among the perimeter countries have led to measurable improvements of existing stocks.

"Overfishing, warming, acidification, pollution, eutrophication, loss of oxygen, intensive use of coasts - all these are phenomena that we observe around the globe. Because they have been particularly drastic in the Baltic, but also because some key problems were successfully addressed, the region can, for good and for bad, tell us what to expect and how to respond to the challenges of the future," Prof. Reusch concludes, "The Baltic Sea, as a model region, can contribute to achieving the United Nation’s Sustainable Development Goal 14 - the conservation and sustainable use of the oceans, seas and marine resources."

Reusch, T. H. B., J. Dierking, H. C. Andersson, E. Bonsdorff, J. Carstensen, M. Casini, M. Czajkowski, B. Hasler, K. Hinsby, K. Hyytiäinen, K. Johannesson, S. Jomaa, V. Jormalainen, H. Kuosa, L. Laikre, C. E. Lee, B. R. MacKenzie, P. Margonski, D. Oesterwind, H. Ojaveer, J. C. Refsgaard, A. Sandström, G. Schwarz, K. Tonderski, M. Winder, M. Zandersen (2018): The Baltic Sea as a time machine for the future coastal ocean. Sci. Adv. 2018;4: eaar8195

Contributing institutions:
GEOMAR Helmholtz Centre for Ocean Research Kiel (German), Swedish Meteorological and Hydrological Institute (Sweden), Abo Akademi University, Turku (Finland), Aarhus University (Denmark), Swedish University of Agricultural Sciences, Uppsala (Sweden), University of Warsaw (Poland), Geological Survey of Denmark and Greenland, Copenhagen (Denmark), University of Helsinki (Finland), University of Gothenburg (Sweden), Helmholtz Centre for Environmental Research Magdeburg (Germany), University of Turku (Finland), Finnish Environmental Institute (SYKE, Finland), Stockholm University (Sweden), University of Wisconsin-Madison (USA), Technical University of Denmark, National Institute of Aquatic Resources, Kongens Lyngby, (Denmark), National Marine Fisheries Research Institute, Gdynia (Poland), Thünen Institute - Institute of Baltic Sea Fisheries, Rostock (Germany), Estonian Marine Institute, University of Tartu, (Estonia), Lulea University of Technology (Sweden), Thünen Institute, Braunschweig (Germany), Linköping University (Sweden)

At images are available for download.

Further information

Dr. Seifeddine Jomaa
UFZ-Department of Aquatic Ecosystem Analysis and Management

UFZ press office

Susanne Hufe
Phone: +49 341 235-1630

In the Helmholtz Centre for Environmental Research (UFZ), scientists conduct research into the causes and consequences of far-reaching environmental changes. Their areas of study cover water resources, ecosystems of the future, environmental technologies and biotechnologies, the effects of chemicals in the environment, modelling and social-scientific issues. The UFZ employs more than 1,100 staff at its sites in Leipzig, Halle and Magdeburg. It is funded by the Federal Government, Saxony and Saxony-Anhalt.

The Helmholtz Association contributes to solving major challenges facing society, science and the economy with top scientific achievements in six research fields: Energy; Earth and Environment; Health; Key Technologies; Matter; and Aeronautics, Space and Transport. With some 39,000 employees in 19 research centres, the Helmholtz Association is Germany’s largest scientific organisation.
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