Hydrogen isotope ratios of terrigenous n-alkanes in lacustrine surface sediment of the Tibetan Plateau record the precipitation signal

Abstract

Hydrogen isotope ratios were measured on terrigenous alkanes (n-C25 to n-C31) extracted from recent lake surface sediments from the climatically and environmentally distinct basins Qiangyong Glacier Lake, Yamzho Lake, Nam Co Lake, Keluke Lake and Xiao Qaidam Lake along a S-N transect in the Tibetan Plateau to explore the climatic implication of these biomarkers. δD values of these n-alkanes are compared to that of precipitation spanning a wide range from -167‰ to -51‰ and clearly correlate with δD values of meteoric water, indicating that terrigenous alkanes record the precipitation signal. The fractionation between precipitation and n-C25, n-C27 alkanes cover a range from -45‰ to -70‰ whilst that between precipitation and n-C29, n-C31 alkanes varies from -70‰ to -95‰ both being fairly constant along the S-N Tibetan transect with the mean at -57‰ and -82‰ respectively. By comparison with the fractionation of -130‰ along the S-N European transect, it implies that the hydrogen isotopic fractionation between meteoric water and terrestrial n-alkanes along the Tibetan transect represent distinct character.