A toolbox approach to measuring carbon stocks and sequestration in the North Sea

Understanding the capacity of marine sediments to store and sequester atmospheric carbon is an essential first step in assessing the possibilities for the management of these stores, including management of pressure such as bottom contacting fisheries, and addressing policy questions such as their potential as nature-based solutions to climate change. Using a toolbox of complimentary techniques for determining carbon abundance, provenance and reactivity, accumulation rates and vulnerability we have analysed a total of 18 sediment cores taken from sites across the North Sea during February and December 2021. Additionally, we have preliminary results from an additional 40 cores taken from a range of sites across the North Sea in June 2023, including across trawling gradients. We present results from our toolbox approach, measuring the carbon stock and sequestration for the cores using a suite of complimentary analyses: from novel techniques such as alkane biomarkers and thermogravimetric analysis (TGA), to radiometric determination of sedimentation rates by lead-210 and stable carbon isotopes (δ13C) in bulk organic carbon, to the more routine techniques such as particle size distribution (PSA), organic & inorganic carbon and nitrogen, porosity, chlorophyll/phaeopigment, and black carbon. We show how viewing the results together can increase the understanding of how carbon is processed in the seabed at a regional scale, and how this can inform where management measures would be most appropriately applied.