Scotland's sedimentary blue carbon : new spatial tools for seabed management

Abstract

Marine sediments are significant long-term stores of carbon. Carbon burial within sediments has provided a climate regulation service over geological timescales. Despite marine sediments holding vast quantities of carbon, the spatial distribution of this carbon store is not well constrained. This information is critical to assessing and monitoring the seabed and in identifying carbon hotspots that may be vulnerable to disturbance and loss. This study focuses on marine sediments within Scotland’s seas. Scotland has a marine area six times its land area making it an exemplar nation to investigate novel methods to improve the spatial understanding of significant sedimentary carbon stores. Here, a novel methodology has been developed that uses multibeam acoustic backscatter data to map surficial sedimentary organic carbon and quantify surface stocks within a model fjordic system. In the proof-of-concept study, a strong correlation between sediment type, backscatter intensity, and organic carbon was found. The heterogeneous nature of the seabed within fjords was highlighted with implications for carbon storage, supporting the need for a greater spatial understanding of marine sediments in carbon accounting. A further study tested the opportunities and limitations of the wider application of backscatter to map sedimentary organic carbon in different coastal settings, potentially providing a cost-effective mapping tool. Results from this project also highlighted the role of estuaries on the east coast of Scotland in delivering significant amounts of terrestrial carbon to inshore sediments. Quality assessments of this organic carbon within shelf sediments indicated that remineralisation losses due to disturbance may be minimal, however anthropogenic pressures on the seabed can affect the burial potential of sediments, thereby limiting the ability of the seabed to provide climate benefits. The findings from this research can be used to provide tools to decision-makers to identify vulnerable carbon stores on the seabed, address evidence gaps relating to the transfer of carbon between ecosystems and implement targeted spatial interventions for their protection.