The Altitude Effect of Leaf Wax-derived n-alkane δD on the Southeastern Tibetan Plateau

Abstract:

This study presents new wax-derived n-alkane δD values (δDwax) from southeast Tibetan Plateau along three vapor thansport paths and determines regional δDwax variation spatially, including the Southern Himalayas transect, the Zayu-Bomi transect and the Lhasa-Bayi transects. Although δDwax values and their lapse rates differ at the three vapor thansport paths, altitude is the predominant factor in determining soil δDwax values along three transects, combined as the Southeast Tibetan Plateau (R2= 0.75; with lapse rate of 2.2‰/100 m). The isotopic altitude effect or the lapse rates of δDwax was more close to river altitudinal gradients along the Southern Himalayas transect. The lapse rate of soil δDwax with altitude is the largest in the Southern Himalaya, due to a large altitude contrast over a short distance, the monsoon precipitation and the monsoonal-driven convection controlling the "amount effect". The lapse rate of the Lhasa-Bayi transect is much smaller than the Southern Himalayas transect and the Zayu-Bomi transect, due to they have experienced intensive evaporation. The smaller altitudinal lapse rate is consistent with the report of the lapse rate of river water δD and δ18O values from the Lhasa River and Nyang branch of the Yarlung Zangbo River. Our results have important implications for the evolution of the southern to central Tibetan Plateau. Paleoelevation reconstructions of the southern to central Tibetan Plateau (Such as Lunpola basin) should take into account the impact of monsoon strength variations (through the amount effect), latitude and (or) vapor transport or distance from the coast, mixing between continental and monsoon-derived moisture, evaporation and recycling of surface water under arid conditions, topography, local environment and climate conditions on the relationships with elevation and δDwax (and linear isotopic lapse rates) for central Tibet.