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Abstract:
Hydrogen isotope ratios of sedimentary biomarkers are known to record the climatic variability in
terrestrial and marine environments. However, there is still a lack of calibration studies that can
quantitatively retrace the driving forces, especially at the Tibetan Plateau. Here, we elaborate the actual
influence of environmental parameters such as temperature, evapotranspiration, salinity and biosynthetic
fractionation on dD values of n-alkanes.
We measured hydrogen isotope values (dD) of n-alkanes in recent sediment and plant samples as well
as dD values of different water sources (lake and inflow water, precipitation as well as leaf, root and soil
water) from six Tibetan lakes along a 10-spanning longitudinal transect covering an aridity gradient. As
expected, the deuterium record can be used to distinguish two water pools at the Plateau: (I) precipitation
water, which supplies water for the lake inflow and terrestrial plants, and (II) enriched lake water
having a clear evaporative signal. Based on significant correlations of the source water and dD values of nalkanes,
dD of alkane n-C23 record the lake water isotope composition and track the evaporative
enrichment of the lake system. In contrast, dD of alkane n-C29 can be used to retrace the isotope
composition of the inflow displaying the integrated rainfall signal in the vegetation period modified by
soil and leaf water evaporation. While temperature changes are less pronounced across the Tibetan
transect, the isotopic difference between C23 and C29 could potentially be used as a proxy to reconstruct
effective moisture (precipitation minus evaporation). Areas with lower precipitation amounts and higher
evaporation rates are characterized by higher DdDC23eC29 values. This relationship is more pronounced in
regions with mean annual precipitation below 350 mm. Even in contrasting environments, the application
of the dD proxies is very promising. Combining other Tibetan studies, it is possible to present a comprehensive picture of the usage of compound-specific hydrogen isotopes of n-alkanes on the Tibetan Plateau
