n-Alkane distribution and carbon stable isotope composition in leaf waxes of C3 and C4 plants from Angola
2015
Badewien, Tanja | Vogts, Angela | Rullkötter, J.
Palaeoenvironmental assessment of past C3 and C4 vegetation distributions relies on end member data from plant analyses. In southwestern Africa, end member data of the carbon number distribution of n-alkanes from leaf waxes and their carbon isotopic composition were available for the rainforest and the savannah. To complement this, we analysed the n-alkane parameters of 41 C3 plants and 11 C4 plants from the transition region, i.e., the wood- and shrubland of Angola. The combined results for the rainforest, the wood- and shrubland and the savannah show an increase in the average chain length (ACL) of C3 and C4 plants and an increasingly enriched carbon stable isotope composition for the C3 plants from the equator towards southern Africa. The enlarged database was applied to the data of a north–south transect of deep-sea surface sediments already used in a previous study, which resulted in the proxies showing a good reflection of the vegetation on the adjacent southwest African continent in terms of %C4 plant cover. Applying end member values for ACL and δ¹³C obtained from the enlarged database by two different averaging methods (arithmetic average and median) to the n-alkane data from the sediment transect yielded similar vegetation reconstructions. In addition, a correlation between ACL and growth height of the plants is discussed, indicating that the ACL may be useful as a tree abundance parameter. Thus, the enlarged end member database strengthens the n-alkane parameters as tools for palaeoenvironmental studies.
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