中文摘要：

通过对秦安大地湾8．3m天然黄土剖面高分辨率（约为150a）孢粉数据的研究，发现秦安地区孢粉数据与我国干旱、半干旱地区史料记载的旱涝演变有较为一致的变化，且有明显的冷干、暖湿的气候特征．奇异谱分析表明，秦安地区的旱涝变化有2300a、1060a、650a和390a的准振荡周期．准两千年周期与南亚季风的变化有密切的对应关系，也与太阳活动的强弱有关．

英文摘要：

A pollen-spore record of an 8. 2 m-long loess section from Qin＇an （35.76°N, 105.82°E） in western Loess Plateau, one of the origins of Chinese civilization, was studied. It provides insights into monsoonal Climate change in this semiarid region, a climatologically sensitive region. The variations of pollen-spore concentration in Qin＇an .are closely related to centennial dry/wet fluctuations in semiarid regions of China in the recent 2 000 years. The abrupt drop of pollen-spore concentration around 3 200 a BP is also consistent with millennium scale dryness and environmental deterioration around 1150-1300 a BC revealed by document records. A singular spectrum analysis suggests that the dry/wet fluctuations in Qin＇an have 2 300 a, 1060 a, 650 a and 390 a periods. The 2 300 a cycle is well correlated to the variations of South Asian monsoon during the Holocene. When South Asian monsoon is strong, the western Loess Plateau is wet, and vice versa. The 2 300 a period is also related to solar variability.