Carbon isotopic composition of alkenes in paleosol with PY-GC-IRMS: Implications for paleovegetation changes on the Loess Plateau, China

Abstract

Weiguo LIU, Yongsong HUANG State Key Lab. of Loess and Quaternary Geology, Institute of Earth and Environment, Chinese Academy of Sciences, Xi'an710075, China," Department of Geological Sciences, Brown University, providence, R102906, USA The carbon isotopic composition of alkenes from loess-paleosol sequences in China Loess was measured by pyrolysis /gas chromatography/isotopic ratio mass spectrometry. Thermochemolysis products of the insoluble residues were characterized using GC/MS, and they are derived mainly from aliphatic hydrocarbons. The dominant aliphatic compounds are n-alkenes that range from C9 to C17 for the loess samples. Fluctuations in the carbon isotopic composition of the Xifeng loess-paleosol profile, range from -27%o to -18.5%o for the past 40 ka. 513C values in colder climates (last glacial) are characterized by depleting in 13C by approximately 3%0 relative to those in warmer climates (deglacial and Holocene). This suggests that the temporal variations of fi13C values for alkenes from plants cutin exhibit a close relationship with glacial-interglacial cycles. The result is also closely consistent with that from total organic carbon in the same loess-paleosol profile. This investigation (1) reveals that plant root contributes a major source of soil organic matter in the China loess deposits, (2) makes it sure that the carbon isotopic composition of the soil total organic matter is a reliable paleovegetation record for the China loess deposits.