Holocene Climate Fluctuations In The Yangtze Delta Of Eastern China And The Neolithic Response
Six major pollen-spore assemblage zones can be identified showing alternate warm and cool climate fluctuations on a millennial timescale. The early-Holocene optimum at c. 8000-7800 radiocarbon years BP, is marked by a large proportion of evergreen broad-leaf species in Zone I, suggesting the warmest/hottest climate setting of the Holocene. The mid-Holocene optimum ran from c. 7500 to 5000 BP (Zone III), during which many subtropical warmand wet-tolerant species represented by Castanopsis and Cyclobalanopsis glauca occurred, indicating the megathermal trend. The temperature then declined upcore in Zone IV accompanied by a high proportion of Pinus and Cupressaceae. A cooling event occurred at c. 4200 BP, as evidenced by Fagus and Potamogeton in the upper section of Zone IV. Pollen assemblages in Zones V-VI indicate a generally cooler temperature in the late Holocene with a high proportion of Gramineae, indicative of rice cultivation. Onset of the mid-Holocene optimum was associated with sediment deposition of the Holocene delta construction. This promoted the migration of Neolithic settlements onto the delta plain from highlands west of the study area. The cooling event recognized at c. 4200-4000 BP may have triggered the cultural ‘break up’ caused by the climatic transition from early warm-humid to a later cool-wet setting, and lake expansion caused by heavy precipitation.