EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Spatially calibrating polycyclic aromatic hydrocarbons (PAHs) as proxies of area burned by vegetation fires

Richard S. Vachula1, Allison Karp2, Elizabeth Denis3, Nicholas Balascio4, Elizabeth Canuel5, and Yongsong Huang6
Richard S. Vachula et al.
  • 1Department of Geosciences, Auburn University, Auburn, USA
  • 2Department of Ecology and Evolutionary Biology, Yale University, New Haven, USA
  • 3Signature Science and Technology Division, Pacific Northwest National Laboratory, Richland, USA
  • 4Department of Geology, College of William and Mary, Williamsburg, USA
  • 5Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, USA
  • 6Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, USA

Many regions worldwide have experienced increasing wildfire activity in recent years and climate changes are predicted to result in more frequent and severe fires. Reconstruction of past fire activity offers paleoenvironmental context for modern and future burning. Pyrogenic polycyclic aromatic hydrocarbons (PAHs) have been increasingly used as a molecular biomarker for fire occurrence in the paleorecord and offer opportunity for nuanced reconstructions of fire characteristics. A suite of PAHs is produced during combustion, and the emission amount and assemblage is influenced by many variables including fuel type, fire temperature, and oxygen availability. Despite recent advances in understanding the controls and taphonomy of these biomass burning markers, the spatial scale of this proxy is unknown. Measurements of PAH fluxes preserved in a lake sediment archive from the Sierra Nevada, California were compared with a historical geographic information system dataset of area burned up to 150 km distance from the lake to determine the spatial scales for which these biomarkers are reliable proxies of burning. The PAH fluxes in the Swamp Lake sediments record a change in the relative anthropogenic and pyrogenic sourcing of PAHs. Anthropogenic pollution sources could explain why some PAHs (fluoranthene (Fl), pyrene (Py), benz[a]anthracene (BaA), retene (Ret), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DA) and ideno[1,2,3-cd]pyrene (IP)) did not correlate with area burned within 150 km. This indicates that individual PAHs may have different efficacies in recording area burned and be more susceptible to masking of fire signals by pollution sources. Despite these complications, we find that the PAHs naphthalene (Na), acenaphthene (Ace), fluorene (F), and anthracene (An) are reliable local proxies of area burned (within 40 km), whereas the PAHs phenanthrene (Phe), chrysene (Ch), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), and benzo[g,h,i]perylene (Bghi) are both reliable local (within 36 km) as well as more regional (as much as 75 km for phenanthrene (Phe), chrysene (Ch), and benzo[g,h,i]perylene (Bghi) or 150 km for benzo[b]fluoranthene (BbF) and benzo[k]fluoranthene (BkF)) area burned proxies. Comparisons of PAH fluxes with charcoal accumulation rates in the same sediments suggest that pyrogenic particulate transport modulates low to mid-molecular weight PAHs via adsorption. Overall, the results indicate that PAH records integrate a combination of spatial signals of area burned and measurement of individual PAHs may enable cross-scale paleofire reconstructions.

How to cite: Vachula, R. S., Karp, A., Denis, E., Balascio, N., Canuel, E., and Huang, Y.: Spatially calibrating polycyclic aromatic hydrocarbons (PAHs) as proxies of area burned by vegetation fires, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6232,, 2022.