Soil n-alkane δD vs. altitude gradients along Mount Gongga, China

Abstract

The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δD p). Here, we present δD values of higher plant-derived C 27, C 29, and C 31 n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δD wax) show significant linear correlations with predicted δD p values ( R 2 = 0.76) with an apparent isotopic enrichment ( ε wax–p) of −137 ± 9‰, indicating that soil δD wax values track overall δD p variation along the entire altitudinal transect. Leaf δD wax is also highly correlated with mountain altitude by a significant quadratic relationship ( R 2 = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δD wax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied ε wax–p values over the slope transect. This study therefore confirms the potential of using leaf δD wax to infer paleoelevations, and more generally, to infer the δD of precipitation.