Blue forests, such as rockweed beds and seagrass meadows, are considered important natural sinks for carbon and thereby play a vital role in climate regulation, mitigation and adaptation. Kelp forests grow on rocky bed substrates and have therefore no local sedimentation of produced biomass. Kelp has therefore not yet been considered to contribute significantly to carbon sequestration and has been left out from the IPCC methodology for blue carbon. However, there is evidence that kelp biomass is transported to deeper seafloor locations where it is sequestered in sediments. The advent of eDNA methods for tracking animal or vegetal organisms in water or sediment matrices, has enabled not only geographical detection without collection of the organism but also temporal study of their presence in dated sediment cores. The eDNA methodology presented here enables sediment species-specific identification of biomass demonstrating the presence of kelp species that were transported and stored away from where they were produced. This technique will make it possible to assess the capacity of atmospheric CO2 draw-down in kelp forests and inform about their potential for carbon sequestration and climate mitigation. The method was initially developed as part of the Nordic Blue Carbon Project (2017–2020).