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The content and hydrogen isotope ratios of n-alkanes extracted from recent lake surface sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed.Values were compared with n-alkanes in plants from lake drainages,and dD values of meteoric water,lake water,and mean annual precipitation.The results showed that n-C23was predominantly derived from aquatic plants,and n-C27–n-C33from terrestrial higher plants.The average carbon chain length of n-C27–n-C33(ACL27–33)was positively correlated with the mean annual precipitation.dD values of the long-chain n-alkanes n-C29and n-C31of terrestrial origin(varying between-214%and-169%,and-226%and-185%,respectively)were inversely correlated with mean annual precipitation;but in accordance with the average annual variations in dD(OIPC),dD values of n-C31were strongly related to the dD values of growing season meteoric water(R2=0.74).The large difference between dD values of n-C23of aquatic origin and n-C31(an average of about 27%)demonstrates the enrichment of the lake water dD compared to precipitation,caused by strong evaporation in the semiarid–arid areas of the southwestern Tibetan Plateau.Average value of en C25 31=p(-95%)is evidently higher than the value observed in European wet regions(-128%);besides,en C31(about-116%)is constant along the study transect(SD=9),which indicates that n-C31is a useful proxy for the environment.
The content and hydrogen isotope ratios of n-alkanes extracted from recent lacustrine sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed. Viruses were compared with n-alkanes in plants from lake drainages, and dD values of meteoric water, lake water, and mean annual precipitation. The results showed that n-C23was predominantly derived from aquatic plants, and n-C27-n-C33from terrestrial higher plants. The average carbon chain length of n-C27-n-C33 ACL27-33) was positively correlated with the mean annual precipitation.dD values of the long-chain n-alkanes n-C29 and n-C31 of terrestrial origin (ranging between-214% and -169%, and -226% and -185% , respectively) were inversely correlated with the mean annual precipitation; but in accordance with the average annual variations in dD (OIPC), dD values of n-C31were strongly related to the dD values of growing season meteoric water (R2 = 0.74). difference between dD values of n-C23of aquatic origin and n-C31 (an average of about 27%) demonstrates the enrichment of the lake water dD compared to precipitation, caused by strong evaporation in the semiarid-arid areas of the southwestern Tibetan Plateau. Average value of en C25 31 = p ( -95%) is evidently higher than the value observed in European wet regions (-128%); besides, en C31 (about-116%) is constant along the study transect useful proxy for the environment.