The burial efficiency of organic carbon (OC BE) was calculated as the ratio
between OC burial and OC gross sedimentation. Gross sedimentation was calculated as the sum of OC burial and OC mineralization. OC mineralization was calculated from porewater profiles of oxygen and methane using Fick’s first law of diffusion. Oxygen fluxes were converted to carbon dioxide fluxesby using a respiratory quotient of 0.9 (Granéli, 1979), and total OC mineralization was then calculated as the sum of CO2and CH4 flux at sediment-water interface. Oxygen exposure time was calculated by dividing the mean oxygen penetration depth by the sedimentation rate.