Fidelity of plant-wax molecular and carbon isotope ratios in a Holocene paleosol sequence from the Chinese Loess Plateau

Abstract

Loess-paleosol sequences from the Chinese Loess Plateau (CLP) provide important archives for paleoclimate reconstruction in the Quaternary. Lipid biomarkers from the CLP have been shown to be useful as molecular paleoclimate proxies. Here, we report a Holocene record of n-alkane ratios and compound specific carbon isotope compositions from the Weinan section on the southern margin of the CLP. Throughout the latest deglaciation (L1-1) and Holocene (S0) layers, the average chain length, carbon preference index (CPI), relative abundance of low molecular weight to high molecular weight n-alkanes, and the δ13C values of n-C29 and n-C31 alkanes varied closely with the changes in paleotemperature and aridity as recorded by tetraether lipids from the same soil samples. Our results are consistent with the expectation that the CLP C4/C3 plant ratio is sensitive to monsoon intensity. Furthermore, the carbon isotope offset between n-C29 and n-C31 alkanes (Δδ13C29–31) correlated closely with the paleoclimate record. Existing data for C4 and C3 herb plants do not support the idea that the close relation between Δδ13C29–31 and paleoclimate results from the isotopic difference between C4 and C3 plants. Instead, it is likely that it arises from climate effects on vegetation dynamics. Although more work is required to confirm this deduction, it appears that the Δδ13C29–31 has potential to be considered a novel paleoclimate proxy in loess-paleosol sequences and similar settings.