长江口水下三角洲^(137)Cs最大蓄积峰的分布特征  

DISTRIBUTION OF THE ^(137)Cs MAXIMUM OF THE SUBAQUEOUS DELTA IN THE YANGTZE RIVER ESTUARY

作　　者：王安东[1] 潘少明[1] 

机构地区：[1]南京大学海岸与海岛开发教育部重点实验室,南京210093

出　　处：《第四纪研究》2011年第2期329-337,共9页Quaternary Sciences

基　　金：国家重点基础研究发展规划项目(973项目)(批准号:2002CB412401)资助

摘　　要：在长江口水下三角洲地区,用^(137)Cs进行沉积速率的测定时,一般认为^(137)Cs最大值所在层位为1963年沉积层。本文通过建立模型,对此进行了计算验证。模型中利用日本东京地区的^(137)Cs年平均大气沉降通量,再通过东京与上海两地的降水量进行校正,并根据不同的沉积速率和取样间隔分别计算出^(137)Cs剖面中的最大值范围,再将理论计算值与实测值进行对比。通过模型的计算,发现理论上沉积物中出现^(137)Cs最大值的层位均为1963年沉积层,将理论最大值范围与本研究所测11根柱样以及前人在本区域所测6根柱样^(137)Cs最大值的对比,发现其中有9根柱样的最大值在理论计算值范围之内。总体上看,理论值与实测值有较好的对应关系,理论值范围基本可作为衡量实测最大值是否为1963年沉积物所在层位的评判标准之一。本文对利用大气沉降^(137)Cs息计算沉积物中^(137)Cs的分布进行了有益的尝试。A series of sediment cores,using the gravity coring equipment,were collected along the Latitude 31.0°N from longitude 122.0°E to 122.5°E in April ＆ November 2006 from the subaqueous delta of Yangtze River Estuary. The length of the cores varied from 100cm to 235cm. Following visual inspection for geological parameters and photography of the cores, the cores were cut at 2-cm intervals for the entire length of the cores. Small aliquots of the sub-samples were selected for grain size distribution measurements, using a Master-sizer 2000 （ Malvern Instruments, UK）. The activities of ^137 Cs were measured by y spectrometry. The counting system is equipped with a 40% efficiency HP Ge detector（GMX30P-A,ORTEC,USA） interfaced to a digital γ ray spectrometer（ ORTEC DSPEC Plus TM）. The sediment samples were sealed in a plastic cup and were counted for 72ksec（ about 20 hours）. In the subaqueous delta of Yangtze River Estuary,it is generally believed that the position of ^137Cs maximum represents the year 1963 when we determine the deposition rates using ^137 Cs dating. In this paper, we validate whether the position of ^137Cs maximum represents the year 1963 in this area by establishing a model. In this model, we used annual ^137Cs deposition at Tokyo and precipitation of Tokyo and Shanghai to carry out the annual ^137Cs deposition in Yangtze River Estuary, and then, we calculated the maximum activity in the ^137Cs profile in the sediment which depended on the deposition rate and the sub-sampling interval. We compared the calculated values with the measured ones. By calculating,we found that the ^137Cs maximum activity represents the year 1963 in the calculated ^137Cs profiles. The ^137Cs maximum decreases with the increasing of the sedimentation rate and the subsampling interval. By comparing the ^137Cs maximum in the 17 profiles（ 11 profiles in this work,and 6 from published data in the subaqueous delta of Yangtze River Estuary） with the calculated values,9 cores gave the results, which showed tha

关 键 词：^137Cs最大值 沉积速率 长江口 

分 类 号：P736[天文地球—海洋地质]