A comparison of equations commonly used to calculate organic carbon content and marine palaeoproductivity from sediment data

• Tested TOC and productivity equations yield different ranges, up to 100% difference.
• Not all equations are able to reproduce measured data, some give unrealistic values.
• Very few equations can be used for both TOC and productivity calculations.

A comparison is made of different methods for calculating total organic carbon (TOC) in deposits and marine primary productivity using sediment data. The calculation methods include both equations derived by pure regression analysis, and equations that include descriptions of processes such as carbon flux and burial efficiency. The results are compared with present-day measured values of total organic carbon and marine primary productivity, using measured sedimentation rate, dry bulk density and water depth. These measurements cover a large range of marine depositional environments, i.e. shallow to deep water, oxic to anoxic conditions, etc. Both TOC and productivity calculations show some consistent over- or under-prediction of computed values compared with the measured values, while some equations lead to unrealistic results. TOC calculations using process descriptions are influenced more by the choice of burial efficiency equation than by the choice of carbon flux equation. Productivity calculations are influenced by the choice of carbon flux equation. Calculations using measured values from a core show that productivity estimates vary by a factor of two.