Accumulation rates of salt-marsh blue carbon at Lindisfarne, northern England, and their relationship with sea-level change

Salt marshes sequester carbon at rates significantly exceeding those found in terrestrial environments. This ability arises from the in-situ production of plant biomass and the effective trapping and storage of both autochthonous and allochthonous organic carbon. The importance of this blue carbon store for mitigating increasing atmospheric carbon dioxide depends on both the rate at which carbon is buried within sediments and the rapidity with which that carbon is remineralised. It has been hypothesized that carbon burial rates, in turn, depend on the local rate of sea-level rise, with faster sea-level rise providing more accommodation space for carbon storage. This study addresses these three key aspects in a salt-marsh sediment study from Lindisfarne, northern England. We quantify rates of carbon accumulation by combining a Bayesian age-depth model based on ²¹⁰Pb and ¹³⁷Cs activities with centimetre-resolution organic carbon density measurements. A Bayesian isotope mixing model pinpoints terrestrial sources as providing the majority of stored carbon. We compare two approaches for assessing the relative proportions of labile and recalcitrant carbon based on a two-pool modelling approach and thermogravimetric analysis. Preliminary results indicate that during the 20^th century more carbon was stored at Lindisfarne salt marsh during decades with relatively high rates of sea-level rise.