Stepped-combustion ¹⁴C dating of bomb carbon in lake sediment

In this study, we applied a stepped-combustion approach to dating post-bomb lake sediment from north-central Mississippi. Samples were combusted at a low temperature (400 °C) and then at 900 °C. The CO₂ was collected separately for both combustions and analyzed. The goal of this work was to develop a methodology to improve the accuracy of ¹⁴C dating of sediment by combusting at a lower temperature and reducing the amount of reworked carbon bound to clay minerals in the sample material. The ¹⁴C fraction modern results for the low and high temperature fractions of these sediments were compared with well-defined ¹³⁷Cs determinations made on sediment taken from the same cores. Comparison of "bomb curves" for ¹⁴C and ¹³⁷Cs indicate that low temperature combustion of sediment improved the accuracy of ¹⁴C dating of the sediment. However, fraction modern results for the low temperature fractions were depressed compared to atmospheric values for the same time frame, possibly the result of carbon mixing and the low sedimentation rate in the lake system.