The Ancient Environment Of The Mount Everest Area Since The Late Miocene

With the rising global temperature,a great deal of environmental problems began to appear around the world,especially the Qinghai-Tibet Plateau,which is sensitive to climate change.In order to provide the basis for the study of the modern regional ecological environment,it's imperative to probe into the regional vegetation and climate evolution of the Qinghai-Tibet Plateau.Referring to the history of Qinghai-Xizang Plateau,paleosporopollen is closely related to paleo-vegetation type,and it is an ideal alternative index for climate record.It has so wide range of distribution and complete data that it's an ideal method for paleovegetation and paleoclimate reconstruction.The average elevation of Mount Everest area is about 4200 meters.It has the typical climate and vegetation characteristics of Qinghai-Tibet Plateau.We can explore the environmental evolution process of the area by using the rich sporopollen data and quantitative analysis methods such as biomisation and climate amplitude method.We have rebuild the paleovegetation and paleoclimate in Mount Everest area by pollen sporopollen analysis and summarized the characteristics of paleoenvironment evolution after the most recent rapid uplift stage.The main results are as follows:(1)A total of 57 sporopollen within 8MaBP in Mount Everest area were collected,all of which belong to 79 genera of 67 families.The majority of angiosperms and gymnosperms are Arbor pollens,while shrubs and herbs pollens(including pteridophytes pollens)are less.(2)According to the trends of sporopollen plant functional types,biomc types and climatic parameters,we divided paleovegetation and paleoclimate evolution into 5 stages: a.The late Miocene to the early Pleistocene: The main vegetation types in this stage are warm temperate evergreen coniferous forest,cold temperate evergreen coniferous forest and temperate deciduous forest.Coniferous Arbor was the dominant sporopollen type.Mainly of the sporopollen plant types are wide temperate species.In terms of climatic parameters,the average rainfall reached its maximum value at 7 MaBP.Then the temperature decreased rapidly,while the annual mean temperature increased several times and decreased.b.The late Pleistocene to the early Pleistocene: The main types of paleovegetation are evergreen coniferous forest in cold temperate zone,followed by mixed forest in cold temperate zone and evergreen coniferous and broadleaved mixed forest in warm temperate zone.The dominance of coniferous trees weakened after 3 MaBP,and shrubs and ferns began to increase slowly.With the increase of temperature,the percentage of plants in cold temperate zone decreased.At the same time,the plant content in warm temperate zone showed the same increasing trend as temperature and precipitation,and reached the maximum value at 0.7MaBP.c.Middle and late Pleistocene: The paleovegetation type is evergreen coniferous forests in the cold temperate zone.There was no significant change in the functional types and climatic parameters of sporopollen plants after 0.52 MaBP,and the environment in the Mount Everest region was in a stable period.d.The late Pleistocene: A variety of vegetation types appeared at this stage,including evergreen coniferous forests in cold temperate zones,mixed grass meadows and temperate grasslands.The sporopollen life types and other parameters changed obviously.The percentage of eurythermic plant,Arbor and soft broadleaved plant decreased rapidly.At the same time,the annual mean temperature also decreased,while the rainfall increased slightly.e.The early Holocene: The main vegetation types in this stage are warm temperate evergreen conifer and broadleaved forest,temperate deciduous broadleaved forest,cold temperate coniferous broadleaved mixed forest and temperate grassland.The dominant sporopollen content of Arbor,eurythermic plant and coniferous plants was no longer dominant,and the percentage of sporopollen content of various plant functional types was gradually balanced.The temperature appears two rise and fall obviously,and the fluctuation of rainfall is tiny.(3)We have discussed the response of paleovegetation to paleoclimate parameters.Shrub and herbaceous sporopollen were decreasing at the beginning and then increasing whlie annual mean temperature was increasing.In addition,shrub and herb sporopollen content increased at first and then decreased with annual rainfall increased.There was a positive correlation between annual mean temperature and warm temperate sporopollen content in climate tolerance.The cold temperate sporopollen content decreased at first and then increased slightly with the annual mean temperature rising.Besides,there was a negative correlation between the sporopollen content of drought-tolerant plants and the annual rainfall.