西藏纳木错现代沉积速率的空间分布特征及近60年来的变化研究  

SPATIAL VARIABILITY OF RECENT SEDIMENTATION RATE AND VARIATIONS IN THE PAST 60 YEARS IN NAM CO,TIBETAN PALTEAU,CHINA

作　　者：王君波[1] 朱立平[1] 汪勇[1] 高少鹏[1] G.Daut 

机构地区：[1]中国科学院青藏高原研究所青藏高原环境变化与地表过程重点实验室,北京100085 [2]Institut fur Geographie, Friedrich-Sehiller-Universitat,07743 Jena, Germany

出　　处：《第四纪研究》2011年第3期535-543,共9页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:40701194和4J071123);国家重点基础研究发展规划项目(973项目)(批准号:2005CB422002)资助

摘　　要：利用^(210)Pb和^(137)Cs方法对采自青藏高原纳木错不同位置的8支岩芯进行了现代沉积速率的研究,其中6支岩芯的^(210)Pb_(ex)比活度变化具有较好的记录,而只有位于湖泊开阔深水区的NMCS08-1岩芯显示了^(137)Cs比活度的蓄积峰。结果显示不同位置岩芯的平均沉积速率具有明显的空间差异,自约1950A.D.以来纳木错不同岩芯的平均沉积速率为0.043～0.098 cm/a,深水区的岩芯显示了较高的沉积速率,但高含水量和低干密度的沉积物特征导致其质量累积速率较低;水深和水下地形以及入湖河流的分布是影响沉积速率的重要因素。近60年来不同岩芯的平均质量累积速率为29.6～61.9mg/cm^2·a,其中3支岩芯的质量累积速率变化显示了较为一致的总体上增加的趋势,且位于开阔深水区的岩芯自1970年以来的变化与湖区降水量记录具有较好的一致性,但显示了一定的时间滞后。Nam Co,located in Central Tibetan Plateau with the position of 30°30′-30°55′N and 90°16′ -91°03′E, is a tectonic-formed lake with the lake level altitude of 4718m a. s. I. The catchment and lake areas are 10610km^2 and 1980km^2, respectively. For investigating the recent sedimentation rate within Nam Co, eight cores were drilled in different locations and recent sedimentation rate study was conducted by using ^210pb and ^137Cs method. The cores are named NMCS08-1 （ position ： 30.74N ,90.79E ）, NMCS07-1 （ 30.83 N ,90.34E ）, NMCS07-3 （ 30.67N ,90.49E ）, NMCS07- 4 （ 30.60N, 90.60E ） , NMCS07 - 6 （ 30.56N, 90.37E ） , NMCS06 - 3 （ 30.68N, 90.73E ） , NMCS06 - 7 （30.66N,90.68E） and NMCS05-9 （30. 86N, 90.87E）. The water depth of drilling sites are 93.5m,46.5m, 74.5m,70.0m, 31.2m, 88.8m, 90.0m and 53.0m, respectively, and the length of the cores are 110cm, 15cm, 30cm,40cm,25cm,25cm, 20crn and 56cm, respectively. Except for NMCS07-3 and NMCS07-4, six cores show rather good ^210pb activity records while only one core（ NMCS08-1 ）from the deep and open part of the lake exhibits cumulative peak of ^137Cs activity. Both CRS （ Constant Rate of ^210Pb Supply） and CIC （ Constant Initial ^210Pb Concentration） models were used to determine the ages of the cores and sedimentation rates. The results show distinct spatial variability of mean sedimentation rates rangeing from 0. 043cm/a to 0. 098cm/a from ca. 1950A. D. among six cores. The cores from deeper area display relative high sedimentation rate but low mass accumulation rate due to high water content and low dry density of sediments. It is suggested that water depth and underwater landform as well as distribution of inflowing rivers were important factors which influence sedimentation rate of a specific site. The mean mass accumulation rate（MAR） ranges from 29.6mg/cm^2·a to 61.9mg/cm^2 ·a in different cores in the last 60 years,and three cores reveal similar increasing trend of MAR in general,the core NMCS08-1

关 键 词：沉积速率 ^210Pb定年 ^137Cs定年 纳木错 青藏高原 

分 类 号：P941.74[天文地球—自然地理学]