中更新世以来青藏高原RH孔和洛川黄土记录的比较研究

COMPARISON STUDY OF RH CORE FROM ZOIGE BASIN WITH LUOCHUAN LOESS RECORD SINCE 800kaB. P.

根据若尔盖盆地RH孔的研究成果，具体地将该孔的21个阶段和洛川黄土记录进行对比，分析其异同点，探讨了高原不同隆升阶段自身环境特点及其对邻近西北干旱区的影响．

Zoige Basin is located in the eastern Qinghai-Xizang Plateau. Core RH (33°54′ N, 102°33′ E )has been sampled from the depth of 120m with the bottom age of 826 ka B. P.,and divided into 21 stages according to the multi-proxy analysis, which can be basically compared with the oxygen isotope record of deep sea core. The good correlation of core RH, loess and oxygen isotope record of deep sea suggests that the climatic change of eastern Qinghai-Xizang Plateau since the middle Pleistocene is mainly characterized by cold-dry and warm-wet fluctuatlons. However, there are discrepancies between the two records from the above-mentioned comparison of the continental records. For example,core RH suggests cold and wet climate for stage 16, whereas Loess Plateau record indicates very dry climate for this period. The authors speculate that the plateau had uplifted to a threshold altitude about 3 000m at some 700kaB. P. At that time the fundamental change of air circulation occurred, i. e. the bottom of the westerlies became into rounding both north and south sides of the plateau from climbing over the plateau originally,resulting in the strengthening of upper westerly trough and hence the intensification of turbulence. Thus a stable Plateau monsoon was established. The plateau might induce the strong southwest monsoon, and did not obstruct obviously the moisture transport into its interior,meanwhile the large scale of ice-snow coverage and increase in albedo made the plateau a cold high pressure cell, hence strengthening Siberia and Mongolia High, which intensifled winter monsoon and restrained summer monsoon to a great extent. This may explain why the maximum glaciation was developed in the plateau, whereas in Loess Plateau coarser and thicker loess was deposited, displaying a cold-dry environment. Afterwards,the plateau accelerated uplift to a new height and acted as a mechanical barrier.This gave rise to the decrease of moisture transportation. There fore, the penultimate glaciation (stages 8 and 6)from core RH is characterized by cold-dry climate, which contrasts with the maximun glaciation. The moisture condition of the plateau itself was deteriorated, and entirely drastic uplift of the plateatl strengthened cold-source and heat-source effect. The Loess Plateau is characterized by the more remarkable alternative sequences of loess and palaeosol, resulting from the evident amplification of monsoon climate cycle signal.