Stepped-combustion C-14 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 degreesC) and then at 900 degreesC. 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 C-14 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 C-14 fraction modem results for the low and high temperature fractions of these sediments were compared with well-defined Cs-137 determinations made on sediment taken from the same cores. Comparison of bomb curves for C-14 and Cs-137 indicate that low temperature combustion of sediment improved the accuracy of C-14 dating of the sediment. However, fraction modem 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.