Abstract
Abstract. Long-chain n-alkanes originate from leaf waxes of higher terrestrial plants, they are relatively resistant against physical and chemical degradation and are preserved in sediment archives for at least millennial timescales. Since their homologue patterns discriminate between vegetation forms, they were increasingly used for paleovegetation reconstructions during the last years. However, before any robust interpretation of the long-chain n-alkane patterns in sediment archives, reference samples from modern vegetation and topsoil material should be investigated at a regional scale. Apart from some temperate and tropical regions, such systematic regional studies on modern plant and topsoil material are still largely lacking.To test the potential of leaf wax-derived n-alkane patterns for paleoenvironmental studies in the semi-humid to semi-arid central southern Caucasus region, we investigated the influence of different vegetation forms on the leaf wax n-alkane signal in modern plants and topsoil material (0–5 cm) from eastern Georgia. We sampled (i) sites with grassland/herbs that included steppe, cultivated grassland and meadows, and (ii) sites that are dominated by deciduous hornbeam forests.The results show that long-chain n-alkanes originate from leaf waxes of higher terrestrial plants and that their homologue pattern allow to discriminate between different vegetation forms: n-Alkanes derived from sites with grassland/herbs are mainly dominated by C31, while n-alkanes derived from sites with deciduous trees/shrubs show high abundances of C29. Thus, long-chain n-alkanes have a great potential when used for regional paleovegetation reconstructions. Moreover, the n-alkane distributions of the topsoils do not show correlations with mean annual temperatures and precipitation along the investigated transect. As degradation of organic matter can affect the leaf wax n-alkane distribution, we further present an updated end-member model that includes our results, accounts for degradation effects and enables semi-quantitative reconstructions of past vegetation changes in the central southern Caucasus region.
Highlights
Long-chain n-alkanes (C25-C35) are produced as part of the epicuticular leaf waxes by terrestrial plants and can serve as valuable biomarkers (Eglinton et al, 1962; Eglinton and Hamilton, 1967; Kolattukudy and Walton, 1973)
The results show that long-chain n-alkanes originate from leaf waxes of higher terrestrial plants and that their homologue pattern allow to discriminate between different vegetation forms: n-Alkanes derived from sites with grassland/herbs are mainly dominated by C31, while n-alkanes derived from sites with deciduous trees/shrubs show high abundances of C29
Leaf wax n-alkanes show a distinct odd-over-even predominance (OEP) (Eglinton and Hamilton, 1967), and their relative odd homologue distribution might be used to differentiate between different vegetation forms: the chain-lengths C27 and C29 are mainly produced by deciduous trees and shrubs, while C31 and C33 mainly derive from grasses and herbs (Marseille et al, 1999; Zech et al, 2010; Schwark et al, 2002)
Summary
Long-chain n-alkanes (C25-C35) are produced as part of the epicuticular leaf waxes by terrestrial plants and can serve as valuable biomarkers (Eglinton et al, 1962; Eglinton and Hamilton, 1967; Kolattukudy and Walton, 1973). Leaf wax n-alkanes show a distinct odd-over-even predominance (OEP) (Eglinton and Hamilton, 1967), and their relative odd homologue distribution might be used to differentiate between different vegetation forms: the chain-lengths C27 and C29 are mainly produced by deciduous trees and shrubs, while C31 and C33 mainly derive from grasses and herbs (Marseille et al, 1999; Zech et al, 2010; Schwark et al, 2002) Because of their low water-solubility and relative persistence against physical and chemical degradation, they stay well preserved in soils and sedimentary archives, over millennial timescales at least (Eglinton and Eglinton, 2008). Bliedtner et al.: Leaf wax n-alkanes from eastern Georgia (Caucasus) plied to various paleoenvironmental archives such as lacustrine and marine sediments and loess–paleosol sequences to reconstruct paleovegetation (Schwark et al, 2002; Schefuß et al, 2003; Zhang et al, 2006; Liu and Huang, 2005; Schatz et al, 2011; Zech et al, 2010; Schäfer et al, 2016a)
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