Assessing the sedimentary carbon sink for climate change mitigation - the need for transdisciplinary cooperation

Shelf sediments represent one of the largest natural carbon sinks on earth. At the same time, shelf regions are increasingly affected by human activity, disturbing sediment reservoirs directly by bottom trawling and offshore construction, or altering the carbon supply by changing river discharge, sediment management and the trophic status and food web of the sea. As global warming progresses, the sedimentary carbon sinks are becoming increasingly important in climate change mitigation measures. Thus, there is a need for in-depth knowledge of both, the dynamics and vulnerabilities of the sedimentary carbon sinks, as well as the legal and political options to protect their sequestration efficiency from human disturbances. Here we report on the transdisciplinary research project APOC, which addresses the Anthropogenic impacts on the cycling of Particulate Organic Carbon in the North Sea. Important results of the project include the quantification of sedimentation rates in the accumulation areas of the German Bight and the Skagerrak, assessing the factors that enhance organic carbon storage and the determination of the sources of deposited carbon. As major anthropogenic disturbances, the effects of bottom trawling and wind farm construction on benthic carbon storage were investigated and assessed. Bottom trawling in particular was significantly decreasing the benthic carbon storage due to a multitude of coupled physical and ecological effects. However, at the environmental policy level, it became clear that sedimentary deposits are not sufficiently recognized as valuable carbon sinks, although their storage capacity is believed to be much higher than that of blue carbon ecosystems at similar latitudes. While the project was staffed mainly with natural scientists, important expertise in environmental policies was provided by the marine protection office of the BUND, one of the largest environmental NGOs in Germany. As a fully-fledged project partner, BUND made it possible to recognize the relevance of the various project focal points for the environmental policy arena throughout the entire project. In turn, the policy experts were able to distribute the latest scientific findings to the relevant political decision makers. In effect, the transdisciplinary cooperation within the project not only produced valuable scientific results, but also numerous expert briefings for environmental policy at all levels, from local authorities to the EU Parliament, emphasizing the importance of protecting sedimentary carbon sinks for climate change mitigation measures. Key to this outcome was the continuous exchange of scientific findings and practical environmental policy knowledge, which kept all participants focused on the societal relevant objectives that were originally pursued with the project funding.