Empirical relationship between leaf wax n-alkane δD and altitude in the Wuyi, Shennongjia and Tianshan Mountains, China: Implications for paleoaltimetry

Estimating past elevation not only provides evidence for vertical movements of the Earth's lithosphere, but also increases our understanding of interactions between tectonics, relief and climate in geological history. Development of biomarker hydrogen isotope-based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance. Here we present leaf wax-derived n-alkane δD (δDwax) values along three soil altitudinal transects, at different latitudes, in the Wuyi, Shennongjia and Tianshan Mountains in China, to investigate δDwax gradients and the apparent fractionation between leaf wax and precipitation (εwax-p).We find that soil δDwax track altitudinal variations of precipitation δD along the three transects that span variable environment conditions and vertical vegetation spectra. An empirical δDwax-altitude relation is therefore established in which the average δDwax lapse rate of − 2.27 ± 0.38‰/100 m is suitable for predicting relative paleoelevation change (relative uplift). The application of this empirical gradient is restricted to phases in the mountain uplift stage when the atmospheric circulation had not distinctly changed and to when the climate was not arid. An empirical δDwax-latitude-altitude formula is also calculated: δDwax = 3.483LAT − 0.0227ALT − 261.5, which gives the preliminary spatial distribution pattern of δDwax in modern China.Mean value of εwax-p in the extreme humid Wuyi Mountains is quite negative (− 154‰), compared to the humid Shennongjia (− 129‰) and the arid (but with abundant summer precipitation) Tianshan Mountains (− 130‰), which suggests aridity or water availability in the growing season is the primary factor controlling soil/sediment εwax-p. Along the Tianshan transects, values of εwax-p are speculated to be constant with altitude; while along the Wuyi and Shennongjia transects, εwax-p are also constant at the low-mid altitudes, but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation δD or the vegetation shift to grass/conifer.Additionally, a reversal of altitude effect in the vertical variation of δDwax was found in the alpine zone of the Tianshan Mountains, which might be caused by atmospheric circulation change with altitude. This implies that the paleo-circulation pattern and its changes should also be evaluated when stable isotope-based paleoaltimetry is applied.

Graphical Abstract106Research Highlights►Leaf wax δD track altitudinal variations of precipitation δD in mountains, China.►An average leaf wax δD lapse rate of − 2.27 ± 0.38‰/100 for empirical paleoaltimetry.►Climate-specific apparent fractionation between leaf wax and precipitation.►Quite negative apparent fractionation (− 150‰) in extremely humid mountains.►A reversal altitude gradient of leaf wax δD caused by atmospheric circulation change.