季风区古环境演化的相似性与人类演化

COMPARISON OF PLIO-PLEISTOCENE CLIMATIC CHANGES IN DIFFERENT MONSOONAL REGIONS AND IMPLICATIONSFOR HUMAN EVOLUTION

通过对东亚季风区、印度季风区及西非季风区上新世一更新世古气候记录的对比，发现这3个地区分别在2．8～2．5MaB．P，1．8～1．6MaB．P．和1．2～0．6MaB．P．前后都发生了明显的气候转型事件。在这些转型事件的前后，气候变化主导性周期发生了明显的改变。此外，这个时期气候变化的主要趋势是干旱程度加剧，或季节性增加。由此说明北半球季风区在长时间尺度上气候变化的相似性，并意味着有一个天文因素以外的，或许存在于地球系统内部的因素控制了气候转型事件。季风区气候变化的整体性有可能对人类演化过程有深刻的调节作用。

The summer monsoonal winds over the Asia-African continents consist of three branches: the East-Asia southeast monsoon, the Indian southwest monsoon and the west African monsoon. As these monsoons are forced by different factors,it would be expected that they may have been established in different ages and undergone adifferent evolution history. To date,the bine when the three monsoon circulations wereinitiated in geologic past is still open to debate,but their evolution in the Plio-Pleistocene period has been relatively completely documented by sediments such ascontinental loess and marine eolian deposits. In this study,we conducted a comparisonof the Plio-Pleistocene climatic records derived from the Chinese Loess Plateau,Arabian Sea and low-latitude Atlantic Ocean. The marine climatic records weregenerated from eolian sediments,thus indicative of changes in intensity of monsoonalwinds or the climate in the source regions. Results show that the eolian sequenceshave recorded three climatic shifts of the Pli0-Pleistocene period.They occurred near 2.8~2.5MaB. P., 1.8~ 1.6Ma B. P. and 1.2~ 0.6 MaB. P., respectively. The 2.8~2.5MaB. P. shift is characterized by the increase in amplitude of climatic oscillationsand the occurrence of the 41 000a tilt periodicity. The 41 000a Period becomepredominant near 1.8~1.6MaB. P. At about 1.0 Ma, the 100 000a climatic Periodappeared and become dominant near 0.6MaB. P. Although the details of climaticchanges in the three regions are not necessarily the same, the similarity of the climatic shifts still suggests a common trends of monsoonal evolution over the Asia-African continents. It is indicated that the similar evolution of the monsoonalcirculations may have important implications for human evolution in the late Cenozoic.