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

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• 作者：Pan Luo ; Ping'an Peng ; Gerd Gleixner ; Zhuo Zheng ; Zhonghe Pang ; Zhongli Ding
• 关键词：leaf wax ; n-alkane ; deuterium/hydrogen isotopic ratio ; inverse altitude effect ; paleoelevation ; paleoaltimetry
• 刊名：Earth and Planetary Science Letters
• 出版年：2011
• 出版时间：3 January 2011
• 年：2011
• 卷：301
• 期：1-2
• 页码：285-296
• 全文大小：1548 K

文摘

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 (δD_wax) values along three soil altitudinal transects, at different latitudes, in the Wuyi, Shennongjia and Tianshan Mountains in China, to investigate δD_wax gradients and the apparent fractionation between leaf wax and precipitation (ε_wax-p).

We find that soil δD_wax track altitudinal variations of precipitation δD along the three transects that span variable environment conditions and vertical vegetation spectra. An empirical δD_wax-altitude relation is therefore established in which the average δD_wax 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 δD_wax–latitude–altitude formula is also calculated: δD_wax = 3.483LAT − 0.0227ALT − 261.5, which gives the preliminary spatial distribution pattern of δD_wax in modern China.

Mean value of ε_wax-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 ε_wax-p. Along the Tianshan transects, values of ε_wax-p are speculated to be constant with altitude; while along the Wuyi and Shennongjia transects, ε_wax-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 δD_wax 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.