CLIMATE CHANGE DURING THE LAST 15,000 YEARS INFERRED FROM PALYNOLOGICAL RECORDS ON THE SONG HONG DELTA AREA, VIETNAM

The palynological sequence from three cores on the Song Hong delta in the northern Vietnam reveals the climate change during the last 15,000 years. The identified pollen in the cores are dominated by Castanopsis (Lithocarpus), Elaeocarpus, Ficus, Piperaceae and Quercus. High percent of temperate including conifers of Dacrydium, Podocarpus, Pinus, Cupressaceae, Txodiaceae and Cryptomeria, and some temperate components of Carpinus, Alnus, Juglans, Carya, Ulmus, Fagus, Ilex, Castanea, Quercus, which mainly distribute on upland, is possibly associated with decline of montane vegetation boundary. After analyzing the magnitude of river influence on pollen assemblages during the sedimentary environment evolution, we extracted the climate information and further to reconstruct climate change. A cooler climate during 14.5-12.9 than at present is indicated by higher percentage of temperate types than at present in the similar environment of floodplain. During 12.9-11.6 cal. kyr BP, the high content of herb prevailed by Artemisia in the sediment of crevasse splay, is possibly associated with widely developed grassland, corresponding to the Younger Dryas cooling period. After a transition period of 11.6-10.9 cal. kyr BP, five cooling periods during 9.4-9.0 cal. kyr BP, 6.5-5.2 cal. kyr BP, 4.53-3.34 cal. kyr BP, 2.10-1.54 cal. kyr BP and 0.63-0.13 cal. kyr BP are indicated by the increase of temperate pollen such as Cryptomeria, Alnus, Quercus, andCastanea.