<jats:title>Abstract</jats:title><jats:p>Organic carbon (OC) burial is an important process influencing atmospheric CO<jats:sub>2</jats:sub> concentration and global climate change; therefore it is essential to obtain information on the factors determining its preservation. The Southern Ocean (SO) is believed to play an important role in sequestering CO<jats:sub>2</jats:sub> from the atmosphere via burial of OC. Here we investigate the degradation of organic-walled dinoflagellate cysts (dinocysts) in two short cores from the SO to obtain information on the factors influencing OC preservation. On the basis of the calculated degradation index <jats:italic>kt</jats:italic>, we conclude that both cores are affected by species-selective aerobic degradation of dinocysts. Further, we calculate a degradation constant <jats:italic>k</jats:italic> using oxygen exposure time derived from the ages of our cores. The constant <jats:italic>k</jats:italic> displays a strong relationship with pore-water O<jats:sub>2</jats:sub>, suggesting that decomposition of OC is dependent on both the bottom- and pore-water O<jats:sub>2</jats:sub> concentrations.</jats:p>