Climatic Significance Of Biomarkersin Soil Samples Along A Transect Between Lhasa(China)-Bharatpur(Nepal)

In recent years, some indicators of biomarker compounds ?n-alkanes, glycerol dialkyl glycerol tetraethers, GDGTs? have made great achievements in the study of palaeoclimate. However, there are large regional differences in different regions. It is of great significance to understand the climatic significance and influencing factors of the index.In this paper, the n-alkanes and glycerol dialkyl glycerol tetraethers ?GDGTs? in surface soil samples from the Lhasa-Nepal transect were analyzed and compared with meteorological records, main achievements are as follows:?1? By analyzing the n-alkanes in different vegetation types, the results indicate that the distribution of n-alkanes in the tropical rain forest and broad-leaved forest shows a bimodal distribution pattern with the highest peaks occurring at C₃₁ and C₂₃, the distribution pattern may be universal in tropical rain forest; in the warm-temperate zone of mixed coniferous and broad-leaved forest, the distribution pattern of long n-alkanes is n-C₃₁> n-C₃₃> n-C₂₇.This distribution pattern of n-alkanes is typical in the forest zone; in alpine shrub and meadow area, n-alkanes are the most abundant in C₃₁, but containing a relatively high content of medium n-alkanes C₂₃.?2? It is found that there is a positive correlation between the average carbon chain length ?ACL? of n-alkanes in the soil and the temperature and rainfall, and the correlation between the carbon dominance index ?CPI? and the temperature and rainfall showing a negative correlation.?3? Results of this study show that two parameters of alkanes (ACL_27-35?CP1_27-35) and the correlation coefficient between the temperature is not too high. However, by fitting the both index of alkanes (ACL_27-35/CPI_27-35), the correlation coefficient between fitting temperature and observed temperature has been improved.?4? The content of glycerol dialkyl glycerol tetraethers ?GDGTs? in the samples are mainly branched-chain ?bGDGTs?, and also small amounts of isoprenoid-type GDGTs ?iGDGTs?. There is a good correlation between branched-chain ?bGDGTs? and environmental factors.?5? The correlation between TEX86 and annual mean temperature and precipitation is weak, and the correlation coefficient R is 0.50 and 0.47 respectively; there is no obvious correlation between the cycling index and the environmental factors; the correlation between MBT and annual mean temperature is high ?R= 0.80?, the MBT is also related to precipitation variation.?6? There is a highly positive correlation between MBT/CBT and temperature and precipitation, the value of the correlation coefficient R is 0.82,0.78 respectively. In the humid areas, the index MBT/CBT is significantly associated with annual average temperature, regardless of the annual average precipitation; in dry regions, MBT/CBT index is weakly associated with annual average temperature and precipitation.