Abstract
Although pyrolysis combined with gas chromatography and mass spectrometry (Py-GC–MS) is widely used for the molecular characterisation of wood, its capabilities to determine the taxonomy (species), provenance, and the nature and intensity of degradation of archaeological woods have been scarcely explored. We performed principal component analysis (PCA) on Py-GC–MS data of sound woods and shipwreck woods of Pinus sp. and Quercus sp., to identify the impact of diagenesis on pyrolysis fingerprints. It was found that the proportion of most polysaccharide products decreased significantly upon diagenesis, with the exception of 3-hydroxy-2-methyl-2-cyclopenten-1-one, which remains relatively well preserved. Furthermore, the guaiacyl lignin products were generally well preserved, except for 4-propylguaiacol, the relative contribution of which decreased considerably. New indices are proposed to establish the preservation state of shipwreck wood (shipwreck wood preservation index; SWPI) based on polysaccharides (SWPIPS) and guaiacyl lignin (SWPILG) and syringyl lignin (SWPILS) fingerprints. Stepwise multiple linear regression analyses applied to FTIR data of the same samples indicate the consistency of both techniques and the potential to identify changes in wood chemistry as a result of degradation. Other factors influencing wood composition, such as the differences between softwood and hardwood lignin and sapwood and heartwood, were also recognised.
