Influence of production variables and starting material on charcoal stable isotopic and molecular characteristics

We present a systematic study oil the effect of starting species, gas composition, temperature, particle size and duration of heating upon the molecular and stable isotope composition of high density (mangrove) and low density (pine) wood. In both pine and mangrove, charcoal was depleted in delta C-13 relative to the starting wood by up to 1.6 parts per thousand and 0.8 parts per thousand, respectively. This is attributed predominantly to the progressive loss of isotopically heavier polysaccharides, and kinetic effects of aromatization during heating. However, the pattern of delta C-13 Change was dependant upon both starting species and atmosphere, with different structural changes associated with chat-coal production from each wood type elucidated by Solid-State C-13 Nuclear Magnetic Resonance Spectroscopy. These are particularly evident at lower temperatures, where variation in the oxygen content of the production atmosphere results in differences in the thermal degradation of cellulose and lignin. It is concluded that production of charcoal from separate species in identical conditions, or from a single sample exposed to different production variables, can result in significantly different delta C-13 of the resulting material, relative to the initial wood. These results have implications for the use of charcoal isotope composition to infer past environmental change. (c) 2008 Elsevier Ltd. All rights reserved.