Prehistoric sea-salt manufacture as an adaptation strategy to coastal flooding in East China

Abstract

Coastal societies are known to be vulnerable to sea-level rise. However, here we report the occurrence of salt manufacturing in the archaeological record of an island of East China that reveals an adaptation strategy by a prehistoric coastal society to sea-level rise through an interdisciplinary study of archaeology and stratigraphy. Archaeological findings and observations of marine microfossils and alkaline earth metals in sediment sequences, together with radiocarbon and optically stimulated luminescence (OSL) dating, reveal that the site was initially occupied at ca. 2900 BCE as an island village with multiple subsistence strategies including hunting, fishing, and stone-tool making associated with the formation of a freshwater dominated coastal plain. Seawater inundation induced by relative sea-level rise occurred at the site at ca. 2400 BCE when Neolithic people constructed elevated mounds and developed specialized sea-salt manufacture in the sheltered tidal flat environment on the island. Evidence from the foraminiferal assemblage suggests that salty soil was scraped from the surface of the adjacent tidal flats and waste material was dumped around the artificial mounds. Micro-structures of the foraminiferal fossils further indicate that these salty soils were air-dried before brine enrichment to produce high-quality salt. Such an economic shift from multiple subsistence into specialized sea-salt manufacture on the island stands in striking contrast to the contemporaneous abandonment of numerous Liangzhu settlements on the adjacent mainland due to coastal flooding. We suggest that prehistoric sea-salt manufacture on the East China coast signifies the resilience of coastal societies in facing the challenge of sea-level rise through exploitation of geographical advantages and marine resources.