Holocene vegetation and climate changes in Hoton-Nur basin, northwest Mongolia

Radiocarbon-dated pollen and diatom records from Hoton-Nur lake(48 degrees 40'N, 88 degrees 18'E), northwest Mongolia an used to reconstruct Holocene vegetetion and climate changes. Steppe, which covered the area some time be fore 9000 BP (all ages are given in C-14 BP), was replaced by boreal conife r forest-steppe by 9000-8500 BP. At the same time, planktonic diatoms incre ased in abundance from 5 to 45%. After 4000 BP there was a sharp reduction in forest and re-establishment of steppe. Changes in the pollen composition were accompanied by a decrease in the abundance of planktonic diatoms from 35-50% (between 9000 and 5500 BP) to less than 10% soon after 4000 BP. The se and other published data from Mongolia suggest wetter conditions during the early and middle Holocene than those of today. This pattern probably re flects an expansion of the Pacific monsoon recorded in geological data from China and simulated in climate-model experiments, and suggests that the su mmer monsoon influenced a larger area than might appear if the Chinese reco rds only are taken into consideration.