【作者】 类延斌；

【导师】 张成君；

【作者基本信息】 兰州大学 ， 环境科学， 2006， 硕士

【摘要】 近几十年来,江河源区的生态环境日趋恶化,干旱化加剧,地下水位下降,水面减少,湿地退化,河流径流量减小,草场退化与沙化加剧等。搞清楚江河源区环境变化的原因对于政府科学决策无疑会具有重要的理论意义。门错位于青海省久治县年保玉则山下,出口河流尼格曲流入黄河,湖区人口密度小,受人类活动影响极其微弱。2004年3月兰州大学和柏林自由大学合作在希门错中心水深50m处采得一长为12.8m的连续岩芯。本文以希门错岩芯作为研究对象,恢复了该区的末次冰期以来的环境变化。 希门错岩芯共有四个AMS年代,底部12.80m处年代严重倒置,故将其舍去不用。由于沉积物中无机碳含量较低,有机质中的碳主要来自大气中的CO₂,碳库效应的影响较弱,在本文中我们没有碳库效应的影响。岩芯的年代序列是通过三个AMS年代线形回归得来。在这个基础上,本文通过有机质含量、磁化率和粒度三个指标恢复了该区近4万年来的环境变化。 岩芯12.80～12.00m（39.5～37ka）与6.25～5.00m环境相似。12.80～7.30m（37.0～22.5kaBP）湖区植被发育较差,冰川规模要大于末次盛冰期。7.30～6.25m（22.5～19.1kaBP）气候寒冷,湖面结冰时间较长。6.25～5.00m（19.1～15.6kaBP）气候寒冷干燥,湖水水位下降,湖面结冰时间仍较长。5.00～3.50m（15.6～11.2kaBP）气温逐渐回升,冰川退缩,湖区植被开始转好。希门错钻孔还揭示了该区末次冰期气候是极不稳定的。新仙女木事件在该区有清楚的表现,其特征是气候寒冷干燥,湖面强烈下降。 希门错钻孔3.50m以上部分代表了全新世以来的环境。3.50～3.10m（11.7～8.1ka）降水较大,但气温仍旧较低,冰川规模还较大。8.4kaBP气候突然变得寒冷干燥,湖水水位下降,与YD事件时的环境相似。3.10～2.25m（8.1～5.9ka）温度较高,降水量较大。6kaBP温度开始下降,标志着全新世适宜期的结束。2.25～0.80m（5.9～2.1ka）气温较低,降水量较小,环境出现剧烈波动。0.8～0m（2.1～0ka）降水继续减少,公元初冷期,中世纪暖期,小冰期在该区都有明确体现。 希门错钻孔还揭示了全新世期间希门错湖区出现了多次气候变干事件,其时间为12.8ka,11.2ka,9.4ka,8.4ka,6.0ka,4.2ka,3.7ka,2.6ka,2.1ka,0.7ka。希门错岩芯记录的环境变化与该区的古冰川遗迹能够较好对比。更多还原

【Abstract】 In recent decades, the ecological environment in Jiang Heyuan region is more and more deteriorating. Finding the reasons of the environmental change in this area will be undoubtedly of great theoretical significance for the scientific decision-making. Nian Bao Yu Ze Mountains is located in Jiu Zhi County in Qinghai Province, with a maximum altitude of 5369m and the growth of modern glaciers in its peak. Rivers in the south of the Mountains run to the Yangtze River, the north into the Yellow River. Ximen Cuo at the north of the Mountains was formed by the erosion of glaciers in ice age, with average water depth of 40m, small population density and extremely weak impact of human activities. The Nigequ River from Ximen Cuo flows into the Yellow River. A 12.8m-long continuous core was drilled at the water depth of 50m in the center of the lake in March 2004.The environmental change in this area is reconstructed in the paper through the lake sediment.Three of the four AMS ages are nearly in a straight line, and the bottom one because of its serious inversion, can not have its eye. Assuming that the age of the surface sediment is zero and the deposition rate of the core is constant, an average deposition rate for the whole of the core is 0.324mm/a through a linear regression of three AMS ages. The age of the bottom of the core is 39.5kaBP, in MIS3 stage. On this basis, the environmental change in this area since 40kaBP is reconstructed through organic content, magnetic susceptibility and grain size.12.80~7.30m (39.5~22.5 ka) glaciers near the lake is largest because of the higher precipitation. 7.30~6.25m (22.5-19.1ka) the climate is coldest and the lake surface is frozen at most of the time. 6.25~5.00m (19.1~15.6ka) the climate is dry and the water level is low. 5.00~3.50m (15.6~11.2ka) the climate become warmer and the water level also increase gradually. Ximen Cuo drilling revealed the climate in the ice age is very unstable.The upper 3.50m of Ximen Cuo core represents the Holocene environment. 3.50~3.10m (11.7~8.1ka) the climate is warmer and wetter. The climate becomes coldand dry suddenly at 8.4kaBP, water level decreases. 3.10~2.25m (8.1~5.9ka) the climate is at its optimum with highest temperature and largest precipitation. Temperature startes to decline at 6kaBP, marking the end of the Holocene optimum. 2.25~0.80m (5.9-2.lka) the temperature decreases dramatically and the precipitation is also lower, with some abrupt climate changes. 0.8~0m (2.1~0 ka) precipitation continued to fall, the temperature experiences several fluctuations. The Medieval Warm period and the Little Ice Age in the area are obvious.Several dry climate events are revealed in Ximen Cuo core, with low lake level. The time is 12.8ka, 11.2 ka, 9.4 ka, 8.4 ka, 6.0 ka, 4.2 ka, 3.7 ka, 2.6 ka, 2. lka, 0.7 ka.更多还原