Hydroclimatic variations in southwestern China during the Middle to Late Holocene transition and effects on the evolution of Late Neolithic cultures in the upper Yangtze River Valley

Abstract

Understanding the effects of hydroclimatic variations on the evolution of Late Neolithic cultures is key to determining the relationships between climate and human society. We reconstructed the hydroclimatic history of southwestern China between 4.9 and 1.1 cal ka BP based on multiple geochemistry proxies, including loss-on-ignition values, total organic carbon and nitrogen contents, degree of humification, and element contents (e.g., Al, Ti, and Zr), as obtained for a peat core from the Caohai Basin in Guizhou Province. The peat record shows two significant centennial-scale droughts at 4.0–3.7 and 2.0–1.7 cal ka BP. The Caohai peat record also shows that wetter conditions existed during the 4.2 ka event (4.3–4.0 cal ka BP), which coincided with hydroclimatic changes throughout the Yangtze River Valley (YRV) and southern China, contrasting with the drier conditions in northern China. The good correlation between the reconstructed hydroclimatic records and archeological evidence on the Chengdu Plain during the Middle to Late Holocene transition (5.0–3.5 cal ka BP) suggests the hydroclimate had an important influence on the evolution of Late Neolithic cultures in the upper YRV. During this transition, the inhabitants on the Chengdu Plain learnt to adapt to hydrological changes by modifying the proportions of different crop types and locations and elevations of walled sites. In addition, near-synchronous hydroclimatic variations at ca. 4.0 cal ka BP suggest that climatic instability led to the decline/collapse of Late Neolithic cultures in the YRV. The demise of the Baodun Culture in the upper YRV occurred during a prolonged drought from 4.0 to 3.7 cal ka BP, which was synchronous with that in southern China, northern India, and the southern Indian Ocean, and was likely due to a contracted Intertropical Convergence Zone and an El Niño-like sea surface temperature state during this period.