Radiocarbon dating of lake sediment using low-temperature combustion

The bulk organic-matter content of near-surface sediment is widely used for radiocarbon (¹⁴C) dating, despite often containing organic carbon (OC) older than the depositional age. Low-temperature combustion can mitigate the influence of old OC, producing ages closer to the depositional age. We developed a simple method to determine the ¹⁴C age of the low-temperature (<250°C) component of bulk sediment. Sediment samples from five Arctic lakes were heated up to 400°C, revealing that at 250°C, about half of the OC combusts, leaving behind the more recalcitrant fraction. We applied this method to 64 samples from late glacial and Holocene sediment cores, analyzing ¹⁴C and % OC in two aliquots: one heated at 250°C and one unheated. The low-temperature ¹⁴C age was calculated by difference using a two-component mixing model. Accuracy was assessed by comparing ages with macrofossils from 48 samples, and reproducibility was tested using a standard reference material. Results show that low-temperature combustion yields ¹⁴C ages with an interquartile range of 115 years, and with reproducibility on par with that of macrofossil dating. On average, the ages differ by 932 years from macrofossils, compared to a 2425-year difference for conventional bulk-sediment ages analyzed in this study. Accuracy improves for samples where the proportion of residual OC after heating is low. This practical and efficient method complements macrofossil dating, supports analysis of a large number of samples, and provides insights into sedimentary carbon cycling.