Holocene n-Fatty Acid Δd Records from Lake Hurleg, Northeastern Tibetan Plateau

Abstract:

The interpretation of δD records from the Tibetan Plateau region remains challenging due to multiple climatic factors influencing on the precipitation isotopic values. Here we study the mechanism of δD variation in this region, by reconstructing the past 10.5 ka n-fatty acid (FA) δD records from sediment core taken in Lake Hurleg on the northeastern Tibetan Plateau and comparing them to the previously presented temperature and moisture data from the same core. Comparison of both C₁₆ and C₂₆ n-FA δD with the average carbon length of n-FA suggests that n-FA δD variability was independent of the n-FA distribution. For δD in the C₂₆ n-FA, it serves as an indicator of hydrogen isotopic signals in terrestrial water. During the Holocene, the heavier C₂₆ n-FA δD values corresponded to millennial cold and wet conditions as inferred by the temperature and salinity records. Thus the terrestrial water δD value changes might be caused by factors other than temperature and moisture, such as the vegetation type and the glacial melt water input. As for the C₁₆ n-FA, although it contains both terrestrial and aquatic source, it mainly mimics the lacustrine water isotopic signal. Therefore, the difference between C₁₆ and C₂₆ n-FA δD can be interpreted as the fractionation between terrestrial and aquatic water induced by evaporation on lake surface. Based on the δD records together with temperature and moisture records, we suggest in millennial timescale, not only stronger precipitation but also less evaporation occurred during the cold periods in the Lake Hurleg region.