Ecologic shift and aridification in the northern Tibetan Plateau revealed by leaf wax n-alkane δ2H and δ13C records

Abstract

Two competing factors, the global cooling and the uplift of Tibetan Plateau, have been proposed to drive the central Asian aridification, but their relative role has seldom been discriminated in paleoclimate and paleoenvironment records. Here, we reconstruct a 14-million-year-long record of paleohydrology and paleoecology in the western Qaidam Basin by applying the compound-specific hydrogen (δ2H) and carbon (δ13C) isotope analyses to terrestrial leaf wax long-chain n-alkanes. The δ2H values are low during the interval of 14.6 to 13.0 Ma. Then the δ2H increases from 13.0 to 12.2 Ma and maintains high values from 12.2 to 3.2 Ma with a peak high value of −156.1‰ at 8.0 Ma. After 3.2 Ma, the δ2H values are low and vary larger than 30‰. The δ13C values decrease from 14.6 to 13.0 Ma and are low from 13.0 to 3.2 Ma except a high value at 3.8 Ma. Then they decrease slightly after 3.2 Ma. Low δ2H values indicate relatively wet climate between 14.6 and 13.0 Ma. The decreasing δ13C values during the same time period support the ecologic shift with the decline of warm component of conifers after the Mid-Miocene Climatic Optimum. High δ2H values since 13.0 Ma are synchronous with the uplift of northern Tibetan Plateau, implying tectonics-driven aridity. Large-amplitude variation in δ2H values since ca. 3.2 Ma seen in East and West Qaidam and lower δ13C values reveal the climatic cyclic responses to the Northern Hemisphere Glaciation.