中文摘要：

岱海两支岩芯独立的高分辨率代用指标序列揭示了季风／干旱过渡区全新世适宜期的气候环境特征。研究表明，在约7．9～3．5kaB．P．期间，岱海流域出现植被繁盛、生产力相对增强和降水丰富的状况，显示气候条件相当适宜；而在约10．0～7．6kaB．P．期间，流域气候以相对干燥为特征。这与早先认为的岱海流域全新世初期为适宜期，且降水丰富的结果明显不同。比较岱海与鄂尔多斯-内蒙古高原中部其他湖沼记录，季风／干旱过渡区的气候适宜期基本集中在约8～3kaB．P．的全新世中期，尽管各记录在适宜期的起止时间、表现特征上存在一些差异。这些差异的产生，一方面可能体现了不同的局地地形、植被、水文条件等对区域水热条件的不同反馈，另一方面则可能暗示不同的沉积序列、测年材料之间难以进行精细的对比。沉积序列的连续性、稳定性及高分辨率、测年材料的适用性是进行全新世气候、环境特征研究的前提。

英文摘要：

The Holocene climate variability has been a main scientific topic while us human beings are facing the challenge of global warming. The hydrological variability has drawn particular attention because a better understanding of its process and reasons is beneficial to the current development and maintenance of the densely populated monsoon area in East Asia. In this paper, characteristics of the Holocene Optimum in the monsoon/arid transition belt of North China are revealed by two independent high-resolution proxy sequences from two parallel sediment cores drilled from the Daihai Lake which is located in Liangcheng County, central Mongolia Plateau based on high-precision AMS ^14C chronology. Data of grain-size, pollen and spores, carbonate content （CaCO3） , total organic carbon and nitrogen （TOC, TN） of two cores both indicate that the vegetation coverage and the productivity of the Daihai Lake drainage area were quite thrived, and the precipitation of the area was also enhanced significantly at ca. 7.9 -3.5kaB. P. , which are evidenced by for example the high level of organic matter and carbonate, the high percentage of tree pollen grains, and the large but variable grain-size. This evidently demonstrated that the optimum climate conditions prevailed during this period due to increased monsoon effective precipitation. During ca. 10.0 - 7.6kaB. P. , the lower level of organic matter, the higher percentage of herb pollen grains and the high carbonate content showed a decreased productivity and a declined vegetation coverage. The higher carbonate content at this stage would have been probably resulted from the higher evaporation ratio of the lake, which also denoted a relatively drier climate conditions. The reconstructed Holocene Optimum by this study has evident discrepancy with what was regarded traditionally that the Holocene Optimum and the monsoon peak precipitation stage occured at the Early Holocene in Daihai Lake area. The Holocene Optimum in monsoon/arid transition belt in North China revealed in