Determination of the abundance and carbon isotope composition of elemental carbon in sediments.

Abstract

We report measurements of the susceptibility of a variety of elemental and organic carbon samples to oxidative degradation using both acid dichromate and basic peroxide reagents. Organic carbon is rapidly oxidized using either reagent, or both reagents sequentially. Elemental carbon exhibits a wide range of susceptibilities to oxidation related both to the degree to which the precursor plant material was carbonized during pyrolysis and to the surface area available for oxidation. Despite a range of susceptibilities, a component of oxidation-resistant elemental carbon has been identified which can be reproducibly separated from organic contaminants. The carbon isotope composition (δ13C value) of the precursor plant materials underwent a 0–1.6‰ decrease during the production of the elemental carbon by pyrolysis, while the subsequent oxidative degradation of the samples resulted in only small (generally < 0.5%o) changes in the δ13C value of the remaining elemental carbon. The results suggest that the technique can be used to obtain records of elemental carbon abundance in marine sediment cores, and thus a record of the intensity of biomass burning on adjacent continental land masses in the geologic past. In addition, the δ13C value of the elemental carbon can provide an indication of the type of vegetation being burnt.