Precipitation in surrounding mountains instead of lowlands facilitated the prosperity of ancient civilizations in the eastern Qaidam Basin of the Tibetan Plateau

Abstract

Precipitation fluctuation has been suggested as a crucial influencing factor in the evolution of ancient civilizations across the world. Nuomuhong culture (~3400–2450 BP) and Tuyuhun (313–663 CE) were unique ancient civilizations that developed in the eastern Qaidam Basin of the north Tibetan Plateau. However, how precipitation variation in the mountain–basin system has affected the rise and fall of these two ancient civilizations is not well understood. Based on analyses of grain size, magnetic susceptibility, Rb/Sr ratio, loss on ignition, and optically stimulated luminescence dates from an aeolian deposit sequence, lowland climate change in the Qaidam Basin during the late Holocene is reconstructed. The Rb/Sr ratio varies from 0.31 to 0.33 during ~2500–2300 BP, it increases from 0.33 to 0.44 during ~2300–1600 BP, and decreases from 0.44 to 0.29 during ~1600–1400 BP, suggesting the climate was relatively dry during ~2500–2300 BP and ~1600–1400 BP and relatively wet during ~2300–1600 BP in the lowlands of the eastern Qaidam Basin, which corresponded well to the gap between the Nuomuhong and Tuyuhun periods. However, the prosperous periods of the Nuomuhong and Tuyuhun were synchronous with high precipitation in the surrounding mountains. Therefore, high precipitation in the surrounding mountains nourished the expansion of oases and then facilitated the development of Nuomuhong and Tuyuhun, which was inconsistent with precipitation variation in the lowlands of eastern Qaidam Basin. The spatiotemporal pattern of precipitation in the mountain–basin system of the Qaidam Basin during the late Holocene was likely affected by solar activity through uplifting–subsiding air flow mechanism, with more precipitation in the mountain and less precipitation in the basin under higher solar activity. A cognitive model is provided to illustrate how solar activity affected the spatiotemporal patterns of precipitation in the mountain–basin structure of the eastern Qaidam, and then human settlement and civilization evolution during the late Holocene.