What happens to the nutrient cycle when typhoons churn the sea: Insights from the eye of the storm
In September 2018, an expedition as part of the German-Chinese project MEGAPOL was affected by the super typhoon “Mangkhut”. This resulted in the collection of unique data sets on the nutrient budget in the impacted part of the South China Sea. Enormous amounts of nutrients were mixed into the surface water from deeper layers, where they tripled the growth of phytoplankton in a few weeks.
As part of the DArgo2025 project, Germany’s Federal Maritime and Hydrographic Agency coordinated the successful validation and deployment of new sensors on automated drifting buoys, so-called Argo floats. These sensors can now be deployed worldwide. In this context, the IOW evaluated novel nutrient sensors that were tested in the Baltic Sea. The project, which ended in December 2021, was funded by the Federal Ministry of Education and Research.
What rivers carry into the Baltic Sea usually ends up in one of its deep basins. Geologists find so-called proxies in these deposits – evidence they use to reconstruct earlier environmental conditions. In a recently published study , Jérôme Kaiser from the IOW and Mathias Lerch from the Max Planck Institute for Demographic Research show that population development and wastewater history in the Baltic Sea region can also be reconstructed in this way – with the help of the remains of faeces!
The fact that sewage sludge from municipal waste water treatment plants contains a high proportion of microplastics has already been shown in earlier studies. It was suspected that the use of such sludge for fertilising fields could also promote the uncontrolled input of microplastics into the wider environment. Now, studies conducted as part of the project MicroCatch_Balt funded by the German Federal Ministry of Education and Research confirm this assumption.
Sea grass is no patent solution for climate change
Regenerating sea grass beds in coastal waters aims at removing carbon dioxide from the atmosphere to fight climate change. However, tropical sea grass beds can release more carbon dioxide than they absorb. This was shown in a study by an international research team led by biogeochemist Bryce Van Dam from the Helmholtz Centre Hereon, in which also scientists from the IOW participated.
A Threat to the Baltic Sea? Long-term development of pollution by polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs) are widespread, highly toxic and often carcinogenic environmental pollutants. Marion Kanwischer from the IOW and her team have studied the long-term development of PAH pollution in the Baltic Sea. Although the overall contamination has eased in recent years, PAHs still pose a toxicological threat to the Baltic Sea. Traffic emissions are a major contributor to the current PAH pollution.
Michael L. Zettler, senior scientist at the IOW, has been researching the occurrence and living conditions of the inhabitants of the seabed of the Baltic Sea and other seas – the so-called zoobenthos – for many years. Now he has contributed his profound expertise to a monograph on the marine bivalves of Germany, thus closing, together with co-author Axel Alf, a gap in the renowned series “Die Tierwelt Deutschlands”.
With detailed analyses of water and sediment samples from the Gotland Basin, geoscientists from the Leibniz Institute for Baltic Sea Research succeeded in tracing the geochemical processes, which followed the Major Baltic Inflow in 2014/2015. Their conclusion: even very large amounts of oxygenated waters cause only small and temporary improvements of the nutrient situation in the central Baltic Sea.
On June 2, 2021, a two-week ship expedition led by the IOW will set out to marine protected areas in the Fehmarnbelt and the Oderbank. The aim of the research cruise is to carry out a comprehensive survey of the seabed’s condition, which, in addition to geophysical and geochemical properties, for the first time also includes the entire near-bottom food web – ranging from bacteria to fishes. The cruise is part of the pilot missions of the German Marine Research Alliance to investigate the impact of bottom trawling on marine protected areas in the North and the Baltic Sea.
Vibrio bacteria, including species that are harmful to humans, are a natural component of Baltic Sea plankton. As a consequence of climate change, they may become more common due to rising water temperatures and thus an increasing health risk. The BaltVib project, coordinated by the IOW, is investigating whether certain plant and animal communities such as seagrass and mussel beds naturally reduce near shore Vibrio abundance and how this effect can be supported through actively shaping the marine environment.