中文摘要：

以210Pb和AMS14C年代为框架，基于青藏高原南部羊卓雍错（简称羊湖）短钻岩芯的粒度记录，通过对沉积物粒度敏感粒级、粒度参数及频率特征曲线分析，重建了青藏高原南部过去近2000年来的有效湿度变化。结果显示：约100～820A．D．，沉积物粒度较细，湖泊水位和有效湿度较高，气候温凉偏湿，对应黑暗时代冷期；820～1200A．D．，粒度变粗，湖泊水位下降，流域气候干旱或有效湿度较低，对应中世纪暖期；1200—1910A．D．，对应小冰期，粒度变细，湖泊水位上升，有效湿度增加，气候湿润，其中在约1200～1320A．D．、1400～1550A．D．和1780～1900A．D．出现3次显著的湿润期，可能对应小冰期的3次较寒冷亚阶段；20世纪以来，湖泊急剧收缩，流域趋于干旱。与太阳活动、北半球温度和亚洲季风指标的对比分析表明：羊湖粒度反映的过去近2000年来有效湿度的变化与青藏高原及其他地区的记录有较好的一致性，但程度和起止时间有所不同；青藏高原南部地区过去2000年来的气候模式为暖干一冷湿，可能主要受太阳辐射强度所控制。该记录可补充青藏高原南部地区过去2000年来湿度变化记录的缺乏，对深人理解季风区高海拔地区过去2000年来气候变化过程及原因有重要的意义。

英文摘要：

The Tibetan Plateau is a sensitive region to climate changes controlled by interactions of large-scale atmospheric circulations, including the East Asian monsoon, Indian monsoon and mid-latitude westerlies. This paper presents a high-resolution humidly reconstruction over the past 2000 years from the sediment of Yamzhog Yumco Lake （28°27′-29°12′N, 90°08′-91°45′E; altitude in 4440m a.s. l.）, a representative inland lake located at southern Tibetan Plateau, China. A suite of 50cm-long cores （29°10′40″N, 90°32′25″E; 4440m a.s.l, and 3.2m in depth） was drilled from the northwest part of the lake using Russian drill in 2013. The cores were mainly composed of clayey silt, intercalated with silt, with minor fine sand and medium-grained sand. 50 grain-size samples were sampled at lcm intervals. 19 samples collected from the upper portion of the core were used in 210Pb dating and two plant materials from the lower portion of the core were dated by AMS 14C dating method. According to the analysis, an age-depth model was established by AMS 14C dating and 210Pb measurements for the past 2000 years. The study on environmentally sensitive grain-size population and comparison with modern hydrologic data implied the clay fraction （7 -10μ m） percentage could be used as a proxy for lake-level change during the past 2000 years. Then, the humidity changes during the past 2000 years in the southern Tibetan Plateau have been reconstructed based on the grain-size recorded from Yamzhog Yumco Lake core, including the clay fraction （7 ~ 10μ m） percentage, grain-size population, grain-size frequency curve and grain-size parameters. The variation of humidity revealed by the reconstruction indicated that there were four periods during the last 2000 years. From 100 to 820A.D., the sediment sizes were finer, suggesting a relatively high lake level and effective moisture, and a moderately wet and cool period corresponding to the Dark Age Cold Period （DACP）. Subsequently, a relatively low lake leve