Sediment core dating to estimate carbon burial rates below seaweed farms

Sediment cores were collected below seaweed farms between October 2020 and October 2021, in order to estimate the carbon burial rates and to compare them to reference sediments beyond the farm and/or prior to the farm operation. Sampling sites represented a total of 20 farms located in 11 different countries distributed globally, including the Americas, Europe, Africa and Asia. The majority of cores were taken manually by divers in shallow waters at <10 m depth. The sampling strategy consisted in collecting 3 cores within the farm area and 2 cores beyond it, as reference sites, which yielded a total of 108 cores. Cores were sliced at 0.5 cm, 1 cm and 2 cm thickness and analyzed for Pb-210, Ra-226, organic carbon and delta C-13. Pb-210 and Ra-226 were used to estimate the excess lead and to model the sedimentation rates over a time period of up to 100 years. Combined with the measurements of organic carbon concentration, carbon burial rates could be calculated at both farm and reference sites.