Preservation of biomolecules in sub-fossil plants from raised peat bogs — a potential paleoenvironmental proxy

The relationship between changes of peat bog hydrology and the mechanisms of decomposition suggests that the chemical modification of biopolymers of peat macrofossils might be used in paleoenvironmental reconstructions. A series of sedge (Eriophorum vaginatum) macrofossils from an Upper Holocene peat profile has been studied by analytical pyrolysis (Py-GC/MS). The major diagenetic changes of biopolymers included loss of ester-bound ferulic and coumaric acids, an increase of oxidation (particularly due to Cα ketones) and shortening of alkyl side-chains, demethylation of methoxy groups of the lignin/polyphenol fraction, loss of pentosan polysaccharides and modification of cellulose (relative increase in the pyrolytic yield of anhydroglucose). The yield of oxidized methoxy-moieties (particularly of Cα ketones) and shortening of alkyl side-chains of methoxyphenols were suggested as the best indicators of oxidative degradation. Statistically significant differences in chemical composition between samples from individual depth increments occur, in part in agreement with a sequence of wet and dry phases determined by paleobotanical analysis. The paleoenvironmental significance of the chemical record of degradation and relationship of paleohydrology reconstructed by the present technique and by means of botanical analysis is discussed. The former was proposed to respond primarily to the frequency of seasonal droughts.