Influence of Different Acid Treatments on the Radiocarbon Content Spectrum of Sedimentary Organic Matter Determined by RPO/Accelerator Mass Spectrometry.

In practice, obtaining radiocarbon (¹⁴C) composition of organic matter (OM) in sediments requires first removing inorganic carbon (IC) by acid-treatment. Two common treatments are acid rinsing and fumigation. Resulting ¹⁴C content obtained by different methods can differ, but underlying causes of these differences remain elusive. To assess the influence of different acid-treatments on ¹⁴C content of sedimentary OM, we examine the variability in ¹⁴C content for a range of marine and river sediments. By comparing results for unacidified and acidified sediments [HCl rinsing (Rinse _HCl ) and HCl fumigation (Fume _HCl )], we demonstrate that the two acid-treatments can affect ¹⁴C content differentially. Our findings suggest that, for low-carbonate samples, Rinse _HCl affects the Fm values due to loss of young labile organic carbon (OC). Fume _HCl makes the Fm values for labile OC decrease, leaving the residual OC older. High-carbonate samples can lose relatively old organic components during Rinse _HCl , causing the Fm values of remaining OC to increase. Fume _HCl can remove thermally labile, usually young, OC and reduce the Fm values. We suggest three factors should be taken into account when using acid to remove carbonate from sediments: IC abundance, proportions of labile and refractory OC, and environmental matrix. [ABSTRACT FROM AUTHOR]