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.

Soil temperature was monitored at 5 soil sampling times and ambient air temperature was monitored at each site throughout the field season. The sampling sites were: Bare soil at higher elevations, namely Observation Bluff, Factory Bluffs, Jane Col and lower parts of Spindrift Col; Soils from below mosses on the Backslope and on Moss Braes. Soils from below higher plant species at Bernsten Point, Factory Bluffs, Moss Braes and North Point. Orthinogenic soils from around penguin colonies at Gourlay Peninsula, Spindrift Rocks and North Point and disturbed soil from around Signy Base.

Field measurements were used to determine the availability of peptide nitrogen to photosynthetic organisms and soil microbes. In order to fully understand their significance in the Maritime Antarctic nitrogen cycle it was also necessary to examine the ability of organisms to utilise the available peptides. For this reason, isotopically-labelled (15N and 13C) nitrogen compounds, including various peptides, were used to determine their rate of uptake by soil microorganisms and plants. These experiments were carried out on Signy to minimise any changes to organisms during transit.