西藏佩枯错早全新世以来湖泊退缩过程及其古环境意义

Shrinkage of Paiku Co since ca.11 ka and its paleo-environmental significance

湖泊的扩张或收缩与冰川融水、大气降水及蒸发量等水文气候因素密切相关。晚第四纪以来,青藏高原许多湖泊经历了显著的水位波动与面积变化,记录了诸多古环境信息并为青藏高原古气候研究提供了重要载体。水位与面积是湖泊演化的关键指标之一。湖泊水位的下降通常会导致入湖河流下切,从而发育河流阶地并出露下伏河湖相地层,因此这些沉积物的年龄和高度为反演湖泊水面的波动历史提供了间接证据。本研究对青藏高原南部佩枯错入湖河流下切的河湖相沉积物进行了光释光定年,结果表明:①约10.0±0.8~11.0±1.3 ka,佩枯错出现拔湖高度大于53 m的高水位,可能与希夏邦马冰川强盛的融水补给有关;②在6.4±0.6~7.4±0.5 ka前后,佩枯错水位出现明显下降,可能反映了季风降水及冰川融水的减少;③在全新世中晚期(约2.1±0.1~3.4±0.2 ka),湖泊水位再次快速下降,可能与季风降水的减弱有关。综上所述,冰川融水与季风降水的协同作用,共同塑造了佩枯错约11 ka以来湖泊的演化历史。

The expansion or shrinkage of lakes links closely to variations in paleo-climatic controls such as glacial meltwater,monsoon precipitation,and evaporation.Many lakes in the Qinghai-Tibetan Plateau experienced significant expansion or shrinkage since the late Quaternary,providing key records for studying regional climate changes.Lake level and coverage area is the most important feature for studying the lake’s history.During lake shrinkage,infilling rivers often incised downwards and form river terraces.Hence these terraces and fluvial/lacustrine sediment exposed can be used to study lake level fluctuation history.Here we present the Optically Stimulated Luminescence(OSL)dating for fluvial and lacustrine sediments in Paiku Co,southern Qinghai-Tibetan Plateau.Our results indicate that:(1)the lake highstand of Paiku Co(more than 53 m)occurred at about 10.0±0.8 ka to 11.0±1.3 ka,probably related to a vigor infill of glacial meltwater from Xixiabangma Mountain;(2)lake level significantly declined at about 6.4±0.6 ka to 7.4±0.5 ka,and we attribute that the reduction of monsoon precipitation and meltwater supply should be the main reason;and(3)the lake level dropped rapidly at about 2.1±0.1 ka to 3.4±0.2 ka,probably associated with a further weakening of monsoon.The results suggest that glacial meltwater and monsoon precipitation coexisted with each other and drove the evolution of the Paiku Co since ca.11 ka.