Stepped-combustion (super 14) C dating of bomb carbon in lake sediment.

Abstract

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 degrees C) and then at 900 degrees C. The CO (sub 2) was collected separately for both combustions and analyzed. The goal of this work was to develop a methodology to improve the accuracy of (super 14) C 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 (super 14) C fraction modern results for the low and high temperature fractions of these sediments were compared with well-defined (super 137) Cs determinations made on sediment taken from the same cores. Comparison of "bomb curves" for (super 14) C and (super 137) Cs indicate that low temperature combustion of sediment improved the accuracy of (super 14) C 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.