Pollen records from southern Taiwan: implications for East Asian summer monsoon variation during the Holocene

Pollen records from two cores retrieved from a valley basin in southern Taiwan show major changes in vegetation and climate occurring during the Holocene. Between 11 400 and 8200 cal. yr BP, the uplands surrounding this valley were dominated by the highland forest components of Maesa, Ardisia, Castanopsis, Cyclobalanopsis, Deutzia, Hydrangea, Ligustrum and Carpinus, which indicates the period was cooler than present. An increase in lowland forest components, such as Aglaia, Phoenix, Calamus, Glochidion and Schefflera, between 8200 and 4100 cal. yr BP, indicates a warmer period than present. It also marks the Holocene thermal optimum. The basin experienced cool climate conditions during the interval 4100 to 2100 cal. yr BP, evidenced by a decrease in lowland forest components. Finally, the climate became warm again from 2100 cal. yr BP, which is analogous to the climate conditions there today. We also identify four submillennial climate phases from pollen assemblages and swamp facies. Highland forest components increased in relative abundance, while the entire valley hosted a herb-dominant swamp, suggesting that the water-table was lower and the climate was cooler. We assert that the East Asian summer monsoon was weaker during these periods (10 600-10 300 cal. yr BP, 9400-8600 cal. yr BP, 7300-7000 cal. yr BP and 5700-5200 cal. yr BP).