Latest pleistocene climate variation of the East Asian monsoon from pollen records of two East China regions

摘要

Pollen analyses performed on borehole cores from the present delta plains of the paleo-Changjiang incised valley and the paleo-Huanghe fluvial, China lead to reconstruction of the latest Pleistocene variation of the East Asian monsoon and permit direct correlation with the vegetation history of eastern China. From 13000 to 11 670 cal yr BP, the short-term climatic deterioration (STCD) possibly corresponding to the Younger Dryas, characterized by cold, dry conditions caused by a strengthened winter monsoon and a weakened summer monsoon, is reflected in the predominance of xerophytic herbaceous pollen (e.g. Artemisia) input, indicative of open grasslands. During the subsequent early post-glacial (PG) interval (11 670-11 270 cal yr BP), pollen of conifer forest-grassland taxa with thermophilous hardwood tree pollen indicate climatic warming (cool, humid conditions). Artemisia/ Chenopodiaceae (A/C) ratios reveal that climatic changes led to increased precipitation at the transition between the STCD and the early PG intervals. Moreover, both the phytogeographic differences and the A/C ratios indicate that during the STCD episode, the humidity levels between the paleo-Changjiang incised valley and the paleo-Huanghe fluvial were different, because they were located in different monsoonal zones. Finally, the possible correspondence of the STCD episode to the YD cold event is believed to indicate that the YD is not confined to the Circum-North Atlantic region, but at minimum is a hemispheric climatic event.