Century‐scale resilience of stored seagrass blue carbon

Blue carbon sequestration in coastal ecosystems is only relevant to climate change mitigation and carbon offset crediting if the carbon is taken out of circulation for at least a century. Here, we examined sediment cores, up to 2.2 m deep, collected in modern Zostera marina seagrass meadows in Mid‐Atlantic lagoons in Virginia, USA. Seagrass was widely abundant here until disease caused regional extinction in 1933. In 1998, 65 yr later, a small naturally seeded seagrass patch was found and spurred a large‐scale seagrass restoration project, now covering more than 40 km2. Integrated data on 210Pb and 14C dating, sediment organic matter and carbon content, and stable isotopic and DNA analysis revealed that a large part of the seagrass organic carbon persisted for centuries despite the absence of seagrass for many decades. In some cases, this legacy blue carbon was double the amount buried in sediments of the restored seagrass meadows.