Normal Alkane Distributions in Soil Samples along a Lhasa-Bharatpur Transect

We present n‐alkane distributions in the soil samples along a transect from Lhasa on the Tibetan Plateau to Bharatpur in Nepal, which covers a large geographical area and a wide range of climatic conditions. These data allow us to assess the significance of n‐alkane distributions in different vegetation types and their relationships to temperature and precipitation. In the tropical rainforest and broadleaved forest zones, n‐alkanes exhibit a bimodal distribution pattern with dominant homologues around n‐C₃₁ and n‐C₂₃. The bimodal distribution of tropical rainforest n‐alkanes may be a general pattern because of the presence of many lianas, epiphytic plants, algae and the strong microbial activity and degradation involved in the postdepositional process. In the warm‐temperate mixed forest and needle‐leaved forest zones, the long‐chain alkanes have a pattern of n‐C₃₁ > n‐C₃₃ » n‐C₂₇. In the alpine shrub and grassland zone, although the most abundant homologue is n‐C₃₁, relatively high n‐C₂₃ concentrations have also been observed in some samples. The statistical results show a good correlation between n‐alkane proxies and climatic factors. The average chain length (ACL) values are positively correlated with precipitation and temperature across the transect. The carbon preference index (CPI) values show a negative correlation with temperature and precipitation along a Lhasa–Bharatpur transect. Although there is a positive relationship between ACL and temperature, it is difficult to separate the two climatic variables (temperature and precipitation) because they are well coupled in the monsoon region.