n-Alkane distribution and carbon stable isotope composition in leaf waxes of C3 and C4 plants from Angola

Palaeoenvironmental assessment of past C-3 and C-4 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 C-3 plants and 11 C-4 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 C-3 and C-4 plants and an increasingly enriched carbon stable isotope composition for the C-3 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 %C-4 plant cover. Applying end member values for ACL and delta C-13 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. (C) 2015 Elsevier Ltd. All rights reserved.