Study On Environmental Change In Zoig(?) Plateau: Evidence From The Vegetation Record Since 24,000 A B.P.

In order to investigate the relationship between the surface pollen and modern vegetation,surface soil samples collected from 34 sites in Zoig(?) Plateau were analyzed,and then the pollen assemblages of each area were obtained.It is found that pollen assemblages of surface soil samples generally reflected the general features of the modern vegetation,basically similar in the spatial distribution,types and the main and dominant genera.But pollen assemblages of surface soil samples aren't completely equivalent to the vegetation composition,maybe because of the influences of humankind's activity,pollen preservation, pollen production,foreign pollen and pollen identification.The representation of pollen in surface soil is different from families and genera.The tree pollens such as Pinus is over-represented,Picea pollens are moderately represented,but Betula isn't over-represented;the herb pollens such as Compositae is well represnted;Artemisia and Chenopodiaceae are equal-represented,but Gramineae and Cyperaceae are under-represented;the fern spores are equal-represented.As a result,this can provide reference to recover paleovegetation and reconstruct paleoclimate in Zoig(?) Plateau.Zoig(?) Plateau is located on the transitional region of modern summer monsoon and Tibet Plateau,not only the west margin of southeast monsoon influenced region,but also the north margin of southwest monsoon influenced region.Due to its sensitivity to the climate change,it is a ideal place for the research of the global climate change.This thesis focuses on the aeolian sands-paleosol layer in attempt to reconstruct the history of climate and environment changes in Zoig(?) Plateau since 24,000 a B.P.,based on AMS-constrained pollen chrono-sequences obtained from Xiaman section.The primary conclusions are as follows:(1) The pollen records of Xiaman section show the course of paleovegetation and paleoclimate evolution in Zoig(?) Plateau since 24,000 a B.P..The cover type is subalpine coniferous forest and the climate is cold and a little dry in 24,564～24,217 a B.P..The cover type is subalpine coniferous forest and the climate is cold and mild wet in 24,217～18,910 a B.P..The cover type is subalpine coniferous forest and the climate is cool and a little dry in 18,910～16,130 a B.P..The cover type is subalpine coniferous forest and the climate is warm and mild wet in 16,130～12,109 a B.P..The cover type is alpine meadow and the climate is cold and mild wet in 12,109～6,460 a B.P..The cover type is subalpine coniferous forest and the climate is warm and a little dry in 6,460～3,999 a B.P..The cover type is subalpine meadow and the climate is warm and wet in 3,999～3,213 a B.P..The cover type is subalpine coniferous forest and the climate is cold and a little dry in 3,213～1,350 a B.P..The cover type is subalpine meadow and the climate is cool and mild wet in 1,350～571 a B.P..The cover type is subalpine coniferous forest and the climate is cold and a little dry in 571～0 a B.P..(2) Since 24,000 a B.P.,the climate and environment changes in Zoig(?) Plateau have the comparison with the peripheral locality of Tibet Plateau and the fluctuation of climate can be responded in other areas each time.The climate is dominated by three primary climate subsystem which is East Asian summer monsoon,southwest monsoon and Plateau monsoon.The environment evolution mechanism possibly is that the intensity of solar radiation makes monsoon changes,thus influence the regional climate and vegetation change.