This dataset contains measurements of the top 50cm of sediment collected between 2021 and 2023 as part of the project sea4soCiety. Sampling took place in three locations each on the North Sea and Baltic Sea coast of Germany, the coasts of peninsular Malaysia and the Caribbean coast of Colombia. To quantify the storage capacity of blue carbon in coastal vegetated ecosystems (mangrove forests, saltmarsh, and seagrass meadows) and unvegetated marine sediments in each location and ecosystem five to nine 50 cm deep sediment cores were collected using a peat sampler (5.2 cm diameter, 50 cm length, Royal Eijkelkamp). Sediment cores were split visually according to visible physicochemical layers and each layer was thoroughly homogenized. Sub-samples for organic matter analyses were frozen at -20°C prior to freeze-drying. Freeze-dried material was pulverized with a ball mill (LLC Planetary Micro Mill PULVERISETTE 7 premium line, FRITSCH) at 500 rpm for 3 min. To determine the organic matter content (containing organic carbon) 3 g freeze-dried and pulverized sediment was stepwise combusted for 4h at 180°C, 300°C, 400°C and 500°C in a muffle oven (M110, Heraeus).

Collections along the German Baltic Sea coast near Massholm, Wendtorf, and Heiligenhafen were made under the permits issued by the Schleswig-Flensburg District Department for Environment Section for Nature Conservation, the Plön District Administrator, Lower Nature Conservation Authority, Office for the Environment (Ref.no.: 3106-3/127/0161), and the District Administrator Department Nature and Soil (Ref.no.: 6.20.2-3117-IV-22-Fr) respectively.Collections along the German North Sea coast in Lower Saxony and Schleswig-Holstein were made under the permit issued by the Lower Saxony Wadden Sea National Park Authority (Ref.no.: 01.2-22249-1-1.1 (60-8) / 2022) and the National Park Administration of the State Agency for Coastal Protection, National Park and Marine Conservation Schleswig-Holstein (Ref.no.: 3141-537.46) respectively.Collections from Colombia along the peninsula of Barú were made under the permit from the Sub-Directorate for Management and Administration of Protected Areas (Ref.no.: 20222000120371).Collections from Malaysia were made under permit from the Ministry of Natural Resources, Environment and Climate Change (Access and benefit-sharing, Ref 974126). The permission to carry out research in Kilim Geoforest Park (Forest Reserve) in Kedah, Malaysia was obtained and approved by the Director-General of the Forestry Department of Peninsular Malaysia (Reference No.: JH/ 100 Jld. 33 (75)). The permit to enter Kilim Geoforest Park (Forest Reserve) in Kedah, Malaysia was obtained from the Langkawi District Forest Office (Permit No.: KL 72.2022).