Abstract

RATIONALE Pyrogenic carbon (C-P) is an important component of the global carbon budget. Accurate determination of the abundance and stable isotope composition of C-P in soils and sediments is crucial for understanding the dynamics of the C-P cycle and interpreting records of biomass burning, climate and vegetation change in the past. Here we test hydrogen pyrolysis (hypy) as a new technique potentially capable of eliminating labile organic carbon (C-L) from total organic carbon (C-T) in a range of matrices in order to enable reliable quantification of both the C-P component of C-T and the stable carbon isotope composition of C-P (delta C-13(P)). METHODS We mixed C-P at a range of concentrations with common C-P-free matrices (C-L = cellulose, chitin, keratin, decomposed wood, leaf litter, grass and algae) and determined the amount of residual carbon not removed by hydrogen pyrolysis (C-R) as a ratio of C-T (C-R/C-T). Mixing C-P with a unique delta C-13 value provided a natural abundance isotope label from which to precisely determine the ratio of C-P to residual C-L remaining after hypy. RESULTS All CP-free matrices contained trace carbon after hypy, indicating that hypy does not remove all the C-L. However, there was a strong correlation between C-R/C-T and C-P/C-T, viz. C-R/C-T=1.02(C-P/C-T)+4.0x10(-3), r(2)=0.99, p 0.001, suggesting that only a small and reasonably constant fraction of C-L remains after hypy. Uncertainties associated with the correction for contamination of C-R by residual C-L are minimal allowing for reliable determinations of both C-P and delta C-13(P) in many cases. CONCLUSIONS Hydrogen pyrolysis appears to be a robust technique for estimating C-P abundance and delta C-13(P) across a range of materials. Nevertheless, caution is required in interpreting delta C-13(P) values when C-P/C-T is low, with C-P/C-T >4% being required for the determination of the delta C-13(P) values within an interpretable error under our experimental conditions. Copyright (C) 2012 John Wiley Sons, Ltd.