This report sets out to provide an improved estimate of the carbon (C) held within Scotland’s marine sedimentary environments across Scotland’s mapped extended Exclusive Economic Zone (i.e. 554,755 km2). Marine sediments accumulating on the ocean floor hold large quantities of carbon (C); these environments can also act to trap and store C over long periods of time (> 103 yrs). The surficial sediments (top 10 cm) of the mapped extended Scottish EEZ holds an estimated 1,515 ± 252 Mt C. The majority of this C is in the form of calcium carbonate (CaCO3), with an estimated 1,294 ± 161 Mt IC being held within the surficial sediments. A significantly lower quantity of C in these surface sediments is stored in the organic form, with an estimated 221 ± 92 Mt OC currently held within the top 10 cm of sediment within Scotland’s mapped extended EEZ.