Hotspots and coldspots of seabed organic carbon on the Norwegian continental margin

Continental margin sediments are important sinks for organic carbon, thus providing valuable climate regulating functions. Human activities such as mobile bottom fishing might, however, compromise the effectiveness of the seabed in accumulating and storing organic carbon through a net increase of organic carbon remineralisation. While there currently is no consensus on the magnitude of this effect, it can be postulated that seabed areas characterised by high rates of organic carbon accumulation, high organic carbon stocks and a large fraction of labile organic matter might be most vulnerable to mobile bottom fishing. Conversely, areas characterised by low or no organic carbon accumulation, low stocks and a small fraction of labile organic matter might be of least concern. Based on reactivity measurements we spatially predict the thermal reactivity of sedimentary organic matter on the Norwegian continental margin. Surface sediments contain between 13% and 34% labile organic matter, with the highest values attained in the central Barents Sea. Using these results and previously developed maps of organic carbon stocks and accumulation rates, we then carry out a regionalisation using unsupervised classification with the aim to identify distinct seabed areas. We identify hotspots with regard to accumulation, storage and lability in the Skagerrak and the central Barents Sea and coldspots on the North Sea plateau, shelf banks in the Norwegian and southern Barents Seas and along the continental shelf break. Our results have the potential to be used in the ecosystem-based management of marine areas in Norway, and our methodology provides a template for similar analyses in other sea areas.