中国风尘堆积与全球干旱化

通过极地冰盖增长、中国风尘堆积(包括西风带下太平洋的风尘沉积)、青藏高原隆起以及现代表面洋流形成过程等资料的分析,初步认为,影响全球干旱化的重要因素之一是极地冷源的作用,山地隆起幅度和洋流变异是干旱化不可忽视的重要因素。据此本文对建立全球干旱化环境序列做一初步尝试。

THE EVOLUTION OF CHINESE AEOLIAN DEPOSITS AND GLOBAL ARIDIFICATION

Basing on the information about aeolian deposits,including those in the Pacific beneaththe westerly,the evolution of bipolar ice sheets,the uplift of Qinghai-Xizang Plateau,thecirculations of the atmosphere and ocean and the evolution of Namib,Sahara deserts inAfrica,the author has preliminarily set up the sequences of global aridification environ-ment.According to the types,rates and southern boundaries of aeolian accumulation it can beshown that the aridification has been strengthened step by step and its processes can be dividedinto different stages.When there was only a single cold source with the Antarctic ice sheet,the red silty dust deposited in China.Since there were bipolar cold sources after onset of theArctic ice sheet,loess has been deposited in China.Now,some marked events of the changesof global environment and aridification can be given as following:At 5 Ma B.P.there were the Antarctic ice sheet with full glaciation and the Qinghai-Xizang Plateau with 1000m mean elevation,the meridional currents of ocean and armospherewere strengthened,the climate at southwestern Cape in southern Africa transited to that ofthe Mediterranean type as the consequence of the Benguela cold current,and the semi-aridclimate in the middle and lower reaches of the Changjiang River to the humid one as theconsequence of the strengthened Asian monsoon.At 2.5 Ma B.P.there were bipolar ice sheetswith half full glaciation and the plateau with 2500m mean elevation,the Chinese aeolian ac-cumulation transformed to loess from the red silty dust,the Mediterranean climate with drysummer came into being at the shores of the Mediterranean as the consequences of the inten-sified Siberian and North Atlantic Subtropical high.The global deserts might become wellestablished.The Milankovitch climatic cycles became more pronounced,which might showthe stability of the ocean-atmosphere subsystem with same oscillation.The above mentionedshow the effect of the bipolar ice sheets and the uplift of Qinghai-Xizang Plateau on the globalaridification.At 0.9 Ma B.P.the bipolar ice sheets were with full glaciation,the Qinghai-Xizang Pla-teau was at 2720m mean elevation and the southern boundary of aeolian accumulation reach-ed 27—29°N.At 0.1 Ma B.P.the plateau was at 4200m mean elevation and the southernboundary reached 23.5°N.At present the plateau is at 4779m mean elevation,after the dust-storm event on April 12,1988 the southern boundary reached 25°N.The above mentioned revealthe evolution processes of paleomonsoon and also show the great effect of the uplift ofQinghai-Xizang Plateau on global aridification.