This dataset presents a harmonised collection of sediment carbon measurements from over 2,000 cores collected across the Southern Ocean and Southern Hemisphere (wider polar front), south of 49degrees. The dataset was compiled to enable quantitative assessments of sedimentary carbon stocks and identify regional hotspots and cold spots of blue carbon, as well as pinpointing trends and gaps in data collection. Drawing on published literature, data repositories, cruise archives, and correspondence with researchers, the compilation addresses longstanding fragmentation and inconsistency in sediment carbon reporting. The database includes measurements of total organic and inorganic carbon (TOC, TIC/CaCO3), and where possible some contextual biological information such as porosity, grain density and grain size. Additionally, where possible, data is georeferenced and cited (inclusive of access links) and further complimentary metadata is provided. The dataset may provide a key resource for future conservation planning, carbon accounting, and potentially climate modelling in polar marine ecosystems. This project was funded by the World Wildlife Fund (WWF) grant number GB096001.

Sediment particle size frequency distributions from the USNL (Unites States Naval Laboratory) box cores were determined optically using a Malvern Mastersizer 2000 He-Ne LASER diffraction sizer and were used to resolve mean particle size, sorting, skewness and kurtosis. Samples were collected on cruises JR16006 and JR17007. Funding was provided by 'The Changing Arctic Ocean Seafloor (ChAOS) - how changing sea ice conditions impact biological communities, biogeochemical processes and ecosystems' project (NE/N015894/1 and NE/P006426/1, 2017-2021), part of the NERC funded Changing Arctic Ocean programme.

Sediment organic material content obtained from replicate 0.1m2 USNL (Unites States Naval Laboratory) box cores are determined by loss on ignition. Samples were collected on cruises JR16006 and JR17007. Funding was provided by 'The Changing Arctic Ocean Seafloor (ChAOS) - how changing sea ice conditions impact biological communities, biogeochemical processes and ecosystems' project (NE/N015894/1 and NE/P006426/1, 2017-2021), part of the NERC funded Changing Arctic Ocean programme.

Sediment cores were collected from the 3 sites (approx. 6m from Moutonnee Valley, 2.5m from Ablation Valley and 5m from Citadel Bastion on Alexander Island). They were analysed for physical property data including: magnetic susceptibility, wet weight, loss on ignition, grain size, isotopic content, bulk carbon, CHN, diatom content, forams, Authigenic carbonate, radiocarbon ages, Strontium and Neodymium content, major, trace and rare earth elements of sediments and clasts and clast lithological analysis. Analyses were carried out at Durham and Edinburgh with isotopic analysis conducted at NIGL (NERC Isotopic Geoscience Laboratory).