耀县黄土记录的全新世东亚冬夏季风非同步演化

通过多指标分析了黄土高原中部地区耀县黄土剖面，重建了全新世以来该地区季风变化过程。结果显示研究区全新世冬、夏季风并非同步演化，夏季风： 10.0～9.4kaB.P.快速转强； 9.4～3.4kaB.P.为全新世强盛期，但夏季风在强盛期并不稳定，其中在 6.8～5.9kaB.P.存在一个衰退事件； 3.4kaB.P.以来夏季风快速衰退。在8.4kaB.P.之前，冬季风强盛，并逐渐减弱； 8.4～6.6kaB.P.冬季风较弱； 6.6～5.7kaB.P.存在一个冬季风突然增强； 5.7～1.7kaB.P.冬季风为全新世最弱的阶段； 1.7kaB.P.以来，冬季风强度迅速增大，具有不稳定性。耀县地区全新世冬、夏季风的演化过程不同步可能揭示了全新世冬、夏季风演化的主控因子不同。

ASYNCHRONOUS EVOLUTION OF EAST ASIA SUMMER AND WINTER MONSOONS OF THE HOLOCENE RECORDED BY YAO COUNTY LOESS

The Loess Plateau lies in the semi­arid zone of North China，where the atmospheric system is controlled by East Asia monsoon. Previous studies indicated that the loess deposits are excellent archives of palaeoenvironmental information and provide some of the most complete continental records of climate change. The research section(34°53′N,108°45′E)is located on the west of the thruway about 50m which is from Xi′an to Tongchuan city，and near the Yao County. The thickness of loess sequences is about 5m，this research only reported the upper 4m. We sampling every 2cm，and gained 190 samples(the upper 20cm of stratum was disturbed by human，no sampling). Every sample made magnetic and grain size analysis. To Contrast with the previous researches and using the magnetic age model to gain a age serial of this research object，the result showed that: the research sequences generated from about 10.3cal.kaB.P.，the S0S3 generated between 9.4～7.5cal.kaB.P.，the S0L2 generated between 7.5～5.9cal.kaB.P.，the S0S2 generated between 5.9～3.4cal.kaB.P.，the S0L1 generated between 3.4～2.3cal.kaB.P.，the S0S1 generated between 2.3～1.6cal.kaB.P. According to previous researches，the magnetic susceptibility of the loess is related to its genesis and can be used as an indicator to rebuild the intensity of ancient summer monsoons，while the particle size of the loess is controlled by the intensity of winter monsoon and can be used as an indicator to rebuild the intensity of ancient winter monsoons. Our study of the magnetic susceptibility and particle size of the loess suggests that the evolution of summer monsoon was asynchronous to the evolution of winter monsoon during the Holocene. The strength of summer monsoon increased very rapidly during 10.0～9.4kaB.P.，reached the strongest during 9.4～3.4kaB.P.，became weak during 6.8～5.9kaB.P.and decayed quickly after 3.4kaB.P. The strength of winter monsoon was very strong before 8.4kaB.P.，then faded gradually and reached a stable state during 8.4～6.6kaB.P.，increased suddenly during 6.6～5.7kaB.P，again became weak and reached the weakest during 5.7～1.7kaB.P.，and again increased quickly but unstably after 1.7kaB.P. The dominate factors of the summer monsoon and the winter monsoon of the Holocene was different. The winter monsoon was controlled mainly by the ice volume of the north hemisphere in Holocene，while the summer monsoon was controlled by both the ice volume of the north hemisphere and the low­latitude insolation intensity. At different latitudes，the relative contribution of the two factors was different. In low­latitude areas，the contribution from insolation was dominant，while at high­latitude areas，the contribution of ice volume was more.