临夏盆地1.95MaBP的气候转型事件与青藏高原隆升作用于大气的临界高度

湖相地层孢粉分析的结果表明，临夏盆地在1．95MaB．P．前后发生过一次重要的气候转型事件。在此之前，南海热带季风信号在地层记录中存在较强的表现，在此之后热带季风信号减弱而高纬冰盖信号加强。CaCO3指标的周期分析同样表明，在1．95MaBP前后确实出现了气候的主导周期转型，在此之前，气候变化周期以类岁差的25kyr周期为主，而在此之后，以类倾角的38kyr周期为主。发生在临夏盆地1．95MaBP的这次气候转型事件表明青藏高原地面在当时隆升到一个可以改变周围地区大气环流的临界高度，如果以青藏高原在2．6MaB．P．- 0．6MaB．P．的平均抬升速率推算，这一临界高度可能在2500m左右。

1.95 Ma B.P. Climate Transition Event and Critical Height of the Effect of Qinghai-Tibet Plateau Uplift on the Atmosphere

Spore-pollen analysis indicates that ~1.95 Ma B.P.is important period of climatic transition in Linxia basin.Before that period the signals of tropical monsoon around South China Sea were well recorded in lacustrine sediment,but after that period signals of tropical monsoon disappeared whereas signals of high latitude ice-sheet whose changes controlled the changes of East Asian monsoon were strengthened in the sediment.Spectral analysis also demonstrated that the dominant climatic cycle in Linxia basin changed from 25 kyr approximating to precession period(23kyr) to 38 kyr approximating to obliquity period(41kyr) at ~1.95 Ma B.P..The climate transition event suggested that Qinghai-Tibet Plateau uplifted to a critical height of its effect on atomosphere.This height may be approximatie 2500m above sea level,according to average uplift rate during 2.6Ma B.P.-0.6Ma B.P..