Compound-specific carbon isotope analysis of short-chain fatty acids from Pine tissues: characterizing paleo-fire residues and plant exudates

Abstract

Different types of plant tissues and resin can account for the wax lipids found in sedimentary contexts and archaeological samples. Consequently, there is increasing research to characterize the fatty acid carbon isotope ratios of different plant anatomical parts and their plant exudates (resin). With the aim to explore isotopic differences between plant tissues, state of the fine organic matter, effect of thermal degradation, and to identify plant residues we measured the δ¹³C values of short-chain fatty acids (δ¹³C_16:0 and δ¹³C_18:0) in: i) dead and fresh (collected and immediately dried) pine needles and branches (Pinus canariensis) and pine resin from laboratory-controlled heating experiments and ii) sediment and charred pine tissue samples from a wild pine forest fire. Our results are compared to previously published experimental open-air fire experiments and pine-fuelled archaeological combustion features. We found that for both fatty acid types, there are differences in δ¹³C signatures among anatomical parts and initial moisture content. These data allow us to characterize the isotopic signature of pine tissue and the effect of degradation on isotopic biomarkers, as well as to estimate combustion temperatures in pine-fuelled anthropogenic fires.

Supplementary information: The online version contains supplementary material available at 10.1007/s12520-023-01815-3.

Keywords: Anthropogenic combustion; Black layers; Degradation of wood; Lipid biomarkers; Organic geochemistry; Organic residue analysis; Pine biomarkers; Pine resin.

Fig. 1

Sedimentary profile (M1) from the pine forest wildfire

Fig. 2

Effect of thermal degradation on δ¹³C_16:0 (A_1-3) and δ¹³C_18:0 (B_1-3) values for fresh and dead Pinus canariensis tissue (1: needles, 2: branches, 3: resin)

Fig. 3

δ¹³C_16:0 and δ¹³C_18:0 values of plant tissues from laboratory-controlled heating experiments in fresh and dead needles (A), fresh and dead branches (B) and resin (C)

Fig. 4

Plots of the δ¹³C_16:0 and δ¹³C_18:0 values of pine tissue from open fire experiments by Buonasera et al. (2019) (A) and pine wildfire (this study) (B). Detailed temperature data of reference samples is given in Fig. 3

Fig. 5

Plots of the δ¹³C_16:0 and δ¹³C_18:0 values of charred organic matter from combustion zone tramples (MFU8 and MFU19, Roques de García Rockshelter, Tomé et al (A) and hearth residues from El Salt (H50) and Crvena Stijena (SU XXIV: BL8,10,11) (Jambrina-Enríquez et al. 2019) (B). These are compared with modern fresh and dead pine reference samples (this study). The modern δ¹³C values were corrected by + 1.9‰ to match archaeological values. WL: white layer; BL: black layer, CT: Combustion residue Trample. Detailed temperature data for reference samples is given in Fig. 3