Charcoal geothermometry continues to offer considerable potential in the study of palaeowildfires over decadal, centennial, millennial, and deep time scales – with substantial implications for the understanding of modern wildfire intensification. Recent developments in the application of Raman spectroscopy to carbonaceous organic material have indicated its capability to potentially reconstruct the palaeocharcoal formation temperature, and equivalent palaeowildfire pyrolysis intensity. Charcoal reflectance geothermometry (which also relies upon microstructural change with thermal maturation) has also been the subject of extensive modern evaluation, with multiple studies highlighting the key influence of energy flux on the resultant charcoal microstructure. The ability to accurately quantify modern wildfire temperatures based upon novel Raman-charcoal analyses has not yet been attempted. Using Raman band width-ratios (i.e., FWHMRa) and accompanying geothermometric trends to natural wildfire charcoals, our results identify differences between microstructurally-derived fire temperatures compared to those recorded during the fire event itself. Subsequent assessments of wildfire energy flux over time indicate no dominant influence for the observed differences, due to the inherent complexity of natural fire systems. Further analysis within this study, regarding the influence of reference pyrolysis methodology on microstructural change, also highlights the difficulty of creating accurate post-fire temperature reconstructions. The application of Raman spectroscopy, however, to the quantification of relative changes in fire temperature continues to prove effective and insightful.
Experimental pyrolysis, Raman spectroscopy and open access publication fees were all supported by funds from the University of Aberdeen School of Geosciences. Organization, generation, and collection of samples during prescribed heathland fire fieldwork was supported by the Macaulay Development Trust Studentship.
We would like to thank Abbie McLaughlin, Sacha Fop, and Struan Simpson (Department of Chemistry, University of Aberdeen) unreservedly for their provision and assistance in the application of Lenton tube furnace equipment. Our sincerest thanks to Donald Barrie (Farm Manager, James Hutton Institute Glensaugh Research Farm) for his help in organizing and managing the prescribed heathland fires. We would also like to thank Sarah Woodin, Louise Ross (School of Biological Sciences, University of Aberdeen) and Alison Hester
(James Hutton Institute) for providing guidance throughout this project, and to Robin Pakeman (James Hutton Institute) for guidance and editorial comments with regards to this article.
- raman spectroscopy
- organic carbon