The Baltic Seafloor in the Anthropocene: from societal pressures to sustainability transformations

The Baltic Sea has a long history of anthropogenic disturbance, that started earlier than in most other coastal oceans and marginal seas. Especially in regions where shallow depths and limited space constrain the area that is available for anthropogenic use, conflicts of interest arise from the rising demand of multiple socio-economic players such as offshore wind, nature conservation, shipping, coastal protection, fishing, military, tourism and many more. The intensive use over many centuries has left long-lasting and partly irreversible traces on the seafloor and the benthic ecosystem. We aim to make the traces of different seafloor modulating processes such as bottom trawling, ship anchoring, propeller wake erosion, seabed constructions or material dumping visible using marine geophysical data of different resolution and spatial coverage. From this data, we can derive the spatial distribution and intensity of anthropogenic disturbances in the Baltic Sea and subsequently evaluate the pressures that they exert in certain areas. This approach is exemplified for propeller wakes that are generated by commercial ships, and that are not yet included in cumulative impact assessments. The results outline how single processes can exert pressures on the entire vertical sea, from the ocean-atmosphere boundary down to the seafloor and below, with likely impacts on ecosystem functioning and marine biodiversity. For propeller wakes, the broad spectrum of direct consequences suggests that the challenges associated with this anthropogenic stressor can only be met and moderated through intensive interdisciplinary research.