青海湖地区冰消期以来气候变化的黄土记录

Palaeoclimate Changes Recorded by Loess Deposit around Qinghai Lake(Northeastern Qinghai-Tibetan Plateau)since Last Deglaciation

青海湖周围堆积着很多黄土和风沙沉积,这些风成沉积序列是过去气候变化的良好记录。相对于湖泊沉积,这些沉积物受到的研究较为薄弱。对青海湖南岸的黄土堆积进行了光释光年代学、磁化率、Fe/Mg值、粒度和有机质含量等气候替代性指标测量。在具有绝对年代标尺控制的基础上,结合气候替代性指标变化特征的分析,表明冰消期以来青海湖地区的古气候经历了多次的冷暖和干湿变化过程:14～9ka间气候前期相对冷干,后期转为凉干,其中可能在11ka左右存在一次暖湿事件;9～2.5ka间气候呈暖湿状态;2.5ka以后的地层扰动较大。黄土和湖泊沉积记录的环境变化过程具有可比性。

Loess and aeolian deposits were found in the area around Qinghai Lake. It is well known that loess is regarded as one of the best terrestrial archives of palaeoclimatic and palaeoenvironmental change. However, investigation on the loess and the aeolian deposits, compared with the lacustrine sediments, is limited and weak in this region. In this paper we dated the loess section by the optically stimulated luminescence （OSL） method, and measured the magnetic susceptibility, Fe/Mg value, grain size distribution and organic matter contents of the Heimahe loess profile. Based on the absolute ages and variations of these climatic proxy indicators, our results show that there are clearly warm/cold and humid/arid alternation in Qinghai Lake area since the late deglaciation. During around 14-9 ka, the palaeolelimate was cold and dry, and it was better only at about I 1 ka. A distinct climate ameliorating occurred from 9 ka to 2.5 ka. Strong disturbance by human activity appeared in loess deposit since 2.5 ka, so it is difficult to analyze the climatic change during the latest Holocene. The environmental changes inferred from the loess deposit are in well comparison with the lacustrine records.