Temporal-Spatial Distribution of the Holocene Vegetation in the Tibetan Plateau
TANG Ling yu, LI Chun hai (Nanjing Institute of Geology and Paleontology, CAS, Nanjing Jiangsu 210008, China)
On the basis of pollen records in the lake cores from 30 sites in the Tibetan Plateau, the temporal-spatial distribution of vegetation, climatic changes and the South Asian monsoon development in the plateau in the Holocene are studied. During the early Holocene (12 ～ 9 ka BP), mixed conifer and deciduous broad leaved forest and mixed deciduous broad leaved forest dominated the vegetation in the east of the plateau (104°～ 98° E). At that time the South Asian monsoon was stronger, with mean annual temperature 2 ～ 4 ℃ higher than that prior to the Holocene and annual precipitation raging from 350 to 550 mm. In the middle of the plateau (98 °～ 92 ° E), meadows or shrub meadows appeared, with annual temperature 4 ～ 4.5 ℃ lower than that of present. Farther west about 80° E, there was a steppe vegetation landscape, which indicated a cold and dry climate.During the middle Holocene (after 9 ～ 3.2 ka BP), from the east to the west of the plateau, the paleo vegetations were, sequentially, mixed conifer and deciduous broad leaved forest or sclerophyllous broad leaved forest conifer (104 °～ 98° E) and mixed deciduous broad leaved forest (98°～ 92° E) or shrub, meadow and steppe (92°～ 80° E). The climate was warmer and wetter than that of the early Holocene. In the southeast, the January temperature was 3 ℃ higher than that of present and the annual precipitation was 250 mm more than that of present. In the northeast, the middle and the south of the plateau, the January temperature was 5 ℃ higher than that of present; and in the west it was 4 ℃ higher than that of present. During the late Holocene (after 3.2 ka BP), from east to west, the paleo vegetations were, sequentially, sclerophyllous broad leaved forest mixed conifer, deciduous broad leaved forest, meadow, steppe and desert. Drop of temperature and precipitation was nonlinear. The January temperature and the July temperature of the southeast were 4 ～ 4.5 ℃ and 3 ～ 3.5 ℃ lower than that of the middle Holocene, respectively, and annual precipitation was 350 mm lower. In the northeast, the forest shrank back and the coldest month temperature was about 8 ℃ lower than that of the middle Holocene. Lake water descended obviously in the west, indicating a very dry climate. Above all, the timing of vegetation and climatic changes supported the result of global climatic-model experiments that suggested a strengthened monsoon system during early to middle Holocene followed by a weakened monsoon system. The South Asian monsoon became stronger from 11 ka BP to 7 ka BP and weakened gradually from 7 ka BP to the present..
【Fund】： 国家自然科学基金项目 ( 4 93710 6 8)资助
【CateGory Index】： Q914
【CateGory Index】： Q914