Extended drought in the interior of Central Asia since the Pliocene reconstructed from sporopollen records

A sporopollen record recovered from 5.3–1.83 Ma sediments was obtained from the lacustrine Yahu section in the central Qaidam Basin of inner Asia. The results provide evidence for vertical zonation of vegetation on the mountains surrounding the basin during the Pliocene and development of forests on the mountains and grasslands around the lake basin. At 3.6 Ma, herbaceous plants (especially xerophytic plants such as Artemisia, Chenopodiaceae and Ephedra) increased for a short time within the basin. Xerophytic plants increased continually after 2.6 Ma in the basin, which exhibited steppe vegetation, and the climate became drier than before. These vegetation changes in the region of the Yahu section suggest a process of stepwise aridification in Central Asia's interior since the Pliocene, and it may be related to global cooling and uplift of the Tibetan Plateau.