青藏高原西南部塔若错湖泊沉积物记录的近300年来气候环境变化

摘要

The 34 cm sediment core, which was recovered from Taro Co, southwestern Tibetan Plateau, was investigated. The multiple indicators in the sediment including the contents of total organic carbon, inorganic carbon, total nitrogen, trace elements and w-alkanes and the ratio of carbon and nitrogen contents were measured. Sedimentation age and rate were analyzed by the method of excessive 21° Pb and 137 Cs dating in order to obtain the continuous sequence of lake sedimentary environment over the past about 300 years. On condition that definitely understanding the climatic and environmental implications of the indicators, the indicators in sediment core were analyzed synthetically and comparatively. Then, the climatic and environmental changes in the region of Taro Co over the past about 300 years were reconstructed according to the dating results. The results showed that the climatic and environmental changes of Taro Co Region could be divided into three obvious stages. In the early stage from 1705 to 1778, the climate, which was warm and humid, fitted the vegetation best in the region. In the middle stage from 1778 to 1860, the last Little Ice Age came, and climate was wet and cold, and the growth of vegetation stopped in the region. In the last stage since 1860, the climate was warm and dry after the Little Ice Age in the region, and the stage could be divided into three small stages: from 1860 to 1924, the climate was dry and a little warm, and the vegetation grew a little; from 1924 to 1969, the climate was a little cold and dry, and the growth of vegetation stopped? Since 1969, the climate was warm, and the drought was improved, and the vegetation grew gradually. The cold and warm alternately recorded by the sediments in Taro Co were highly consistent with that recorded by ice core in Guliya and lake sediments in Qinghai Lake; however, there were differences in the beginning and end years of the stages.%以青藏高原西南部塔若错的34 cm浅湖芯为研究对象,对其沉积物样品进行总有机碳、无机碳、总氮、微量元素、正构烷烃含量及碳氮比等多项指标的分析测定.采用过剩210pb和137 CS计年法对该湖芯进行了定年和沉积速率研究,获得了近300年的连续湖泊沉积环境序列.在明确了各指标气候环境指示意义的前提下,综合对比分析湖芯中各项气候环境指标,并结合定年结果重建了塔若错湖区近300年来的气候环境变化.结果表明:塔若错湖区气候环境变化可分为3个明显阶段:早期为1705～1778年,该地区气候环境温暖湿润,湖区植被广泛发育；中期为1778～1860年,湖区处于小冰期末次阶段,气候环境寒冷而湿润,植被发育受阻；后期为1860年至今,为小冰期结束后偏暖干化时期.其中,后期又可分为3个亚阶段:1860～1924年,湖区气候环境稍暖且干旱,植被稍有发育；1924～1969年,湖区气候环境呈现偏冷干特点,植被发育暂缓；1969年至今,湖区气候回暖,环境干旱化有所缓解,植被开始逐渐发育.在气候冷暖变化上,该湖芯记录与古里雅冰芯记录和青海湖湖泊沉积记录都有较好的可对比性,只是在起讫年代上存在一些差异.