The concentrations of microplastics in the surface layer of the oceans are lower than expected. Researchers at the GEOMAR Helmholtz Centre for Ocean Research Kiel, the Kiel Cluster of Excellence “The Future Ocean” and the Helmholtz-Zentrum Geesthacht experimentally demonstrated that microplastics interact with natural particles and form aggregates in seawater. This aggregate formation could explain how microplastics sink into deeper water layers.