Comparison of the paleoclimatic significance of higher land plant biomarker concentrations and pollen data: A case study of lake sediments from the Holsteinian interglacial

Abstract

A sediment core from the Dethlingen paleolake (Holsteinian interglacial, northern Germany) was subjected to integrated organic geochemical and palynological/paleobotanical analyses in order to reconstruct past environmental conditions. The fractionated lipid extracts were investigated using gas chromatography–mass spectrometry (GC–MS) and GC–combustion–isotopic ratio-MS. Ring A aromatized pentacyclic triterpenoids, most likely glutinane derivatives, were the only higher-plant-derived pentacyclic triterpenoids found. The saturated ring A degraded triterpenoid des-A-lupane was the most abundant aliphatic hydrocarbon throughout the core. Based on published pollen data, which imply the strong presence of Betula and Alnus around the paleolake, the des-A-lupane would be expected to originate mainly from lupane-type precursors synthesized by Betulaceae. The carbon isotopic composition of des-A-lupane varied from −28.2‰ to −30.6‰ and no significant trend or isotopic shift was observed. However, the discrepancy between the variation in pollen data and biomarker concentration (i.e. quasi-absence of diterpenoids) in the core argues for a scenario in which the two proxies represent different components of the vegetation in the catchment area of the paleolake.