Preliminary Study On Quaternary Environmental Change In The Central Tibetan Plateau

Tibetan Plateau is the focus of global geo-science research. Uplifting of Tibetan Plateau and its significance to the global material and energy transportation and balance, to the forming and evolution of atmospheric circulation pattern and Asian monsoon, become the high lights of geo-sciences. This dissertation is a part of the achievements of the "973" project titled "Uplifting process of Tibetan and climate and environment change in East Asian", which discussed the Quaternary environment change in the central Tibetan Plateau based on the high solution study on the lake sediments. According to the lithology and sedimentation cycle of CE core (200m) in Co Ngoin Lake, the uplifting process and environment change since 2.8MaBP can be divided into some stages as below. Around 2.8Ma, the plateau uplifted intensively and the surface of plateau disintegrated. After 2.8MaBP, the uplifting period were 2.67~2.26MaBP, around 1.77MaBP, around 1.06MaBP and after 0.82MaBP, in which it uplifted more intensively during 2.67~2.26MaBP. During 2.26～2.02MaBP, 1.77～1.06MaBP and 1.05～0.82MaBP it was relatively calm. The analyses of environmental indexes of the sediment from a 5.3m core, CE-2 core, taken from Co Ngoin lake, reveals the process of climate change in the central Tibetan Plateau during 12~4kaBP, shown as cold and wet period (before 11.2kaBP) →Allerod period (11.2～10.9kaBP)→Younger Dryas (10.9～10.5kaBP)→warm and wet period (Holocene, after 10.5kaBP). The climate still varied in Holocene and some drying events occurred (9.2kaBP, 8.2kaBP, 7.5～7.3kaBP, 6.4kaBP, 5.5～5.4kaBP and 4.3kaBP). After 4.3kaBP, it became dryer and the lake shrank strongly. The climate change reflected the monsoon variations: after unstable stage of 12~10.5kaBP, monsoon enhanced since 10.5kaBP, and began to weaken slightly since 9.5kaBP; the stronger period of monsoon is between 9.0~6.1kaBP; after 6.1kaBP the monsoon weakened again. A quantitative correlation between carbon and oxygen isotopes of authigenic carbonates from lake sediments can easily be derived. This method need not to consider complicated physical and chemical process of lake, provides an easy, direct and efficient way to quantitative restore paleoclimate history. The major feature of climate change in Co Ngoin Lake area is that it changed dramatically at the early 20th century. Before 1900AD it was cold and dry; after 1900AD, precipitation increased obviously, and the lake expanded. Temperature had an obvious increase after 1935AD, and reached its peak value in 1940s. After slightly decrease since 1950s, the temperature increased since 1980s.