Climatic implication of hydrogen isotope ratios of terrigenous n-alkanes in lacustrine surface sediment of the Tibetan Plateau

Abstract

δD values of terrigenous n-alkanes (n-C 25 , n-C 27 , n-C 29 and n-C 31 ) extracted from recent lake surface sediments of Lake Qiangyong Glacier, Lake Kongmu Co, Lake Nam Co, Lake Keluke and Lake Xiao Qaidam along the S-N transect of Tibetan Plateau are compared to those of precipitation spanning a wide range from -167‰ to -51‰ and clearly correlate with δD values of meteoric water during the growth, indicating that terrigenous n-alkanes record the precipitation signal during the growth. The isotopic fractionation between precipitation and alkanes of n-C 25 and n-C 27 cover a range from -45‰ to -70‰ whilst that between precipitation and alkanes of n-C 29 and n-C 31 vary 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 apparent isotope fractionation of -130‰ along the S-N European transect, it implies that the apparent hydrogen isotopic fractionation between meteoric water and terrestrial n-alkanes along the Tibetan transect is much smaller.