Climatic Implication Of Hydrogen Isotope Ratios Of Individual N-Alkanes In Lacustrine Sediment On The Tibetan Plateau

To explore the climatic implication of compound-specific hydrogen isotope ratios of sedimentary n-alkanes, the author sampled shallow sediment cores respectively from the climatically and environmentally distinct basins Qiangyong Glacier Lake,Kongmu Co Lake,Nam Co Lake, Keluke Lake and Xiao Qaidam Lake along a S-N transect on the Tibetan Plateau for the extraction and analysis of these biomarkers.δD values of terrigenous n-alkanes (n-C25, n-C27, n-C29 and n-C31) extracted from recent lake surface sediments from the five lakes along the S-N transect are compared to that of precipitation spanning a wide range from -167‰to -51‰and clearly correlate withδD values of meteoric water during the growth, indicating that terrigenous n-alkanes record the precipitation signal during the growth. The fractionation between precipitation and alkanes of n-C25 and n-C27 cover a range from -45‰to -70‰whilst that between precipitation and alkanes of n-C29 and n-C31 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 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.δD values of aquatic derived n-alkanes (n-C17, n-C19, n-C21 and n-C23) extracted from recent lake surface sediments from the five lakes along the S-N transect are compared to that of lake water spanning a wide range from -135‰to -22‰and the results show that these biomarkers do not record lake water signal. The fractionation between lake water and algae derived alkanes of n-C17 and n-C19 cover a range from -30‰to -170‰whereas that between lake water and submerged/floating plants derived alkanes of n-C21 and n-C23 varies from -40‰to -160‰, both covering a wide range along the S–N Tibetan transect with the mean at -94‰and -93‰, respectively. By comparison with the constant fractionation of -157‰along the S–N European transect, it implies that the hydrogen isotope fractionation between source water and sedimentary aquatic n-alkanes may not be necessarily constant at -157‰in different regions.δD values of terrigenous n-alkanes (n-C25, n-C27, n-C29 and n-C31) extracted from a short sediment profile spanning the past near-50 years at 7-year resolution from Kongmu Co Lake on the southern Tibetan Plateau are compared to the climate elements of Langkazi and Lhasa weather stations and clearly correlate with mean annual air temperature and significantly correlate with mean growing season air temperature, indicating that these biomarkers record the air temperature signal during the growth and have the potential to be used as a paleotemperature proxy.