Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5161493 | Organic Geochemistry | 2016 | 35 Pages |
Abstract
We studied the high-resolution and well-dated 25,000 year sedimentary record of Lake Challa, a deep tropical crater lake in equatorial East Africa, to explore new proxies for paleoenvironmental and paleohydrological change. Sedimentary biomarker analysis revealed the presence of des-A-triterpenoids with oleanane, ursane and lupane carbon skeletons, microbial degradation products of angiosperm plant triterpenoids. Their increased influx from 16,000 years ago corresponds with previously documented changes in the terrestrial vegetation of the Lake Challa basin during postglacial warming, in particular the relative increase in C3/C4 plant ratio inferred from the stable carbon isotopic signature (δ13C) of sedimentary n-alkanes derived from plant leaf waxes. In contrast to this n-alkane δ13C signature, the δ13C of des-A-lupane maintains a constant value of â27.4 ± 1.1â° across the glacial-interglacial transition. Since des-A-lupane is derived from C3 plants, its δ13C signature is here proposed to represent a novel and independent proxy for the time-variable carbon isotopic composition of local terrestrial C3 plants, which can improve estimates of the C3/C4 plant ratio based on two-end member mixing models of n-alkane δ13C values.
Related Topics
Physical Sciences and Engineering
Chemistry
Organic Chemistry
Authors
L.G.J. van Bree, W.I.C. Rijpstra, N.A. Al-Dhabi, D. Verschuren, J.S. Sinninghe Damsté, J.W. de Leeuw,