Last Deglacial Vegetation And Climate Change Revealed By Pollen Record From The Lugu Lake, Southwest China

The studies of climate in the last deglaciation, the transitional period from the the Last Glacial Maximum to the Holocene, are important to understanding the dynamics of the earth climate system from one state to another and predicting future climate changes. The Lugu Lake as the study object is located in the northwestern Yunnan of southwest China, influenced by both Southeast Asian and Southwest monsoon. It is sensitive to climate changes, and thus is an ideal region for the study of climate abrupt changes. High-resolution pollen analysis on 520-580 cm lake sediments of core LGH-2 from the Lugu Lake was carried out to reconstruct vegetation successions and climate changes of the last deglaciation. The depth-age model of the study core was established from 9 AMS14 C dates and the correlation of CaCO3 contents between cores. Several conclusions were obtained from this study:1. The Lugu Lake with a specific location and large area is less affected by human activities, and its lake sediments are continuous and stable, it thus is an ideal area for the environmental studies and reconstructions of vegetation succession and climate change.2. Pollen analysis of surface pollen samples around the Lugu Lake show that those modern pollen spectra not only reflect the overall feature of regional vegetation,they also exhibit properties of local vegetation, therefore, fossil pollen spectra from sediments of the Lugu Lake did represent regional vegetation in the drainage area of the Lugu Lake.3. The result of pollen analysis shows there are four pollen zones can be partitioned in the whole pollen assemblages and each zone is mainly characterized with the growth and decline of trees and shrubs, herbaceous pollen percentages.The trees and shrubs pollen percentages are high in zone I,III,IV, but in the zone II diminished. The herbaceous pollen percentages are relative low.4. High-resolution pollen analysis on 520-580 cm lake sediments of core LGH-2from the Lugu Lake shows four phase changes of vegetation secession and climate variation during the last deglaciation. Phase I(16500~16000 a BP, the early period ofthe last deglaciation): climatic conditions were cold with a increase trend in temperature and humid, and precipitation was high. Phase II(16000~15500 a BP,the early B?lling-Aller?d warm period): temperature rose and humidity increased,climatic conditions developed to more suitable. Phase III(15500-14500 a BP, main part of B?lling-Aller?d warm period): both temperature and humidity increased to the highest,and vegetation was the flourish. Phase IV(14500-13500 a BP,the late B?lling-Aller?d warm period): temperature was still high. The Lugu Lake valley also experienced several centennial cold events during the last deglaciation. Among them,one may be related to H1 event, a global cold event, and others are probably the regional events in the drainage region of the Lugu Lake.5. Comparison of this reconstructed climate record with other climate records was carried to reveal mechanisms of climate changes during the last deglaciation.Cold and humid climate in the early deglaciation was probably associated with the block of thermohaline circulation in the North Atlantic, which was caused by the North Atlantic ice raft event. The climate during the mid- and late deglaciation was controlled by solar radiations, and temperature rose and humidity increased.