Assessment of the relationship between ACL/CPI values of long chain n-alkanes and climate for the application of paleoclimate over the Tibetan Plateau

Abstract

Leaf wax n-alkanes are one of the most abundant molecular biomarkers, and they have tremendous potential for climate study. To understand the relationship between distribution characteristics of terrestrial higher plant long chain n-alkanes and climate, we assessed the correlation between average chain length (ACL25-33)/carbon preference index (CPI25-33) and mean annual temperature (MAT), growing season temperature (GST), and mean annual precipitation (MAP) and growing season precipitation (GSP) over the Tibetan Plateau (TP). It is important to note that the distribution characteristics of these long chain n-alkanes must be determined in surface soils and surface lake sediments. Statistical analysis and multi-proxy approaches (CPI and Paq) were applied to deal with this problem. The answer was that the long-chain n-alkanes corresponding to the conditions (CPI25-33≥5, aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio Paq≤0.20) were basically derived from terrestrial higher plants. Using these long chain n-alkanes to assess the correlation between ACL25-33/CPI25-33 and MAT, GST, MAP and GSP, we concluded that (i) weak positive correlations between ACL25-33 and MAT/GST were observed on the TP. Under high temperatures, the ACL values of terrestrial higher plants will increase to reduce cuticular transpiration. (ii) there are negative relationships between CPI25-33 and MAP/GSP. (iii) based on the studies of two proxies (ACL and CPI) for paleoclimate application, the long-chain n-alkane ACL25-33 may become a useful qualitative indicator of temperature change in paleoclimate studies from Xining Basin, Ximen Co, Glacially eroded lake, and Lake Dangxiong Co on the TP. CPI25-33 values might serve as a qualitative indicator of precipitation in paleoclimate studies when the plant species do not vary on the TP.