The potential use of sedimentary pyrogenic biomarkers to quantitatively reconstruct wildfires occurrence and extension

We have developed and applied new analytical methodologies to study the drivers of the spatial distribution of pyrogenic biomarkers throughout the Iberian Peninsula. The goal of the study is to develop a multiproxy pyrogenic biomarker approach to quantitatively reconstruct the paleo-occurrence and extension of biomass wildfires from sediments. For this purpose, we have compiled an extensive collection of lacustrine sediments throughout Spain. The sample suite is representative of a wide range of climates and ecosystems. We have quantified the abundance of different types of pyrogenic biomarkers such as BPCAs (benzene polycarboxylic acids derived from the chemical oxydation of pyrogenic carbon), MAS (monosaccharide anhydrides, namely levoglucosan) and PAHs (polyaromatic hydrocarbons namely with 4 or more rings). The data obtained, as concentrations or ratios, has been mapped and compared to the documented occurrence and extension of wildfires in Spain over the last 5 decades. Specifically, we have calculated the burned area within different radius around the lake, and correlated them against the biomarker data. 

The regional distribution of fires in Spain is the primary driver of the spatial distribution of pyrogenic biomarkers in lakes sediments. Thus, the sedimentary concentration of pyrogenic biomarkers, generally, correlates with the area of burned forest land within a radius of 10-20km. Work is still under way to decipher the meaning between the correlations of different types of pyrogenic biomarkers, and the relation between biomarker ratios and fire regimes and vegetation types. Our study shows that pyrogenic biomarkers in lakes can be used as paleoproxies to study regional fires, as opposed to those occurring at larger spatial scales. It remains to be seen, how our findings  from Spanish lakes can be extrapolated  to other continental regions.  Nonetheless, our study validates their use to quantify the area of forest burned in the region surrounding the lake, in addition to the frequency of fires in the past.