Mid-Holocene salinity intrusion and rice yield loss on East China coast and the impacts on formation of a complex state society

The East China coast is a significant center of Neolithic culture. However, the drivers for the formation of prehistoric Liangzhu State, which emerged at ca. 5300 cal. yr BP and is considered the earliest example in China of a complex state society, have yet to be discerned. This study presents multi-proxy analyses of chronology, sedimentology, organic and alkaline-earth metal geochemistry, diatoms, and phytoliths in sediments collected from the Neolithic Yingjia site located on the south bank of Hangzhou Bay in the East China coastal lowlands. Our aim is to investigate hydrological changes and associated responses of rice farming from the late Hemudu to Liangzhu periods. Results indicate that a freshwater wetland dominated by C3 plants started forming at the site at ∼5900 cal. yr BP, while rice cultivation emerged there at the same time. A persistent rise in salinity, leading to a decline in rice yield, was observed between ca. 5350–4900 cal. yr BP, as indicated by an increase in Sr concentrations and the percentages of brackish water diatom species, as well as a decline in rice phytoliths. A layer of organic-rich mud that exhibits a decrease in freshwater planktonic diatoms at ca. 5100 cal. yr BP demonstrates a closed local environment, inferring a drier climate. Our analysis suggests that an observed salinity intrusion during ca. 5350–4900 cal. yr BP was mainly caused by typhoon events and exacerbated by the dry climate. Concurrent typhoon events were also documented at other Neolithic sites found on both the south and north banks of Hangzhou Bay. However, the domestication of rice was not interrupted in the region, as evidenced by the high proportion of rice bulliforms with ≥9 fish-scale decorations, despite the occurrence of unstable climate events including both frequent typhoons and droughts. We speculated that the climate instability may have stimulated the emergence of the well-organized prehistoric complex society of Liangzhu Culture, which was more resilient in the face of natural disasters. This claim is also examined in the context of climatic and cultural changes recorded across Africa and the eastern Mediterranean.