Lignin and Isotope Signatures in Pollen: A Caveat of Lignin Phenol Biomarker for Reconstructing Paleovegetation

Abstract

Lignin phenol and stable isotope have been used as a biomarker to trace the sources of sedimentary organic matter (SOM), reconstruction of paleovegetation and climate changes without considering the possible occurrence of fossil pollen grain in sedimentary matrix. Lignin phenol analysis of modern pollen showed that both gymnosperm and angiosperm pollen yielded very high concentration of cinnamyl (C) phenols as compared to that of vanillyl (V) and syringyl (S) phenols (C/V=3.05–23.67) with variation in isotopic compositions (δ $^{13}$ =−20.2 to −28.3‰ and δ $^{15}$ N =−9.2 to 1.7‰). Therefore the isotopic and lignin phenol signatures in SOM might be distorted to some extent by fossil pollen. This was especially true in the sediments of low altitude and latitude continental lakes and coastal areas where significant amount of fossil pollen might be deposited. Therefore, before using lignin phenol as a biomarker, one should consider a possible distortion derived from lignin of fossil pollen in sedimentary matrix.