摘要
本文运用同步辐射X射线荧光光谱原位微区分析方法对湖光岩玛珥湖湖泊沉积物进行了分析,以核素测年(137Cs、210Pb和AMS 14C)数据为时间标尺,获得了1200年来Ti、Fe、Cu、Zn、Rb和Br等元素含量的高分辨率数据.Br元素含量与当地气象记录降水量变化大致呈正相关,可能说明区域降水是Br元素含量变化的主要影响因素.对1200年来Br元素含量的谱分析结果表明,Br元素含量变化的准周期分别为:1.5a、1.9～2.0a、2.1～2.6a、2.9～3.0a、374～442a和221～256a.其中,年际准周期变化可能与厄尔尼诺相关,而百年尺度的变化可能与太阳活动有关.从Ti元素含量与器测数据对比来看,Ti元素含量较高的时期也对应于降水量较大的时段,降水增加可能有利于碎屑物的搬运,但植被覆盖度、粒度效应等因素对沉积物中Ti元素存在正-负反馈机制.
Abstract
Climate change of the past 2000 years is a key scientific project both in "Past Global Changes" and "Climate Variability and Predictability".However,it is difficult to connect paleoclimatic records and modern instrumental data due to limitation in high-resolution paleoclimatic data by traditional geochemical analysis,which is limited to sampling precision.Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) in-situ analysis is a new method developed in recent years,which could realize high-resolution at seasonal to yearly timescale.Huguangyan M aar Lake (21 °09′N,110° 17′E) belongs to the Lei Q iong Volcanic Field,located twenty kilometers southwest of Zhanjiang City,Guangdong Province.It is a closed lake with a surface area of 2.3km2 and catchment of 3.5km2.Because of its closed natural and a lack of stream inputs,it makes this site a natural weather station and an ideal candidate for paleoclimatic archives.Here,we present a high resolution paleoclimate reconstruction of the past 1200 years from a 1.0m-long sediment core in Hugangyan Maar Lake.Age control in the core is based on 137Cs,210Pb and AMS 14C data.Radiocarbon dating was done by accelerator mass spectrometry on leaves picked in 53cm and 94cm of the core from Hugangyan.Two 14C ages were calibrated to calendar years,1212A.D.and 815A.D.,using the atmospheric decadal data set from the calibration program CALIB 4.3.Elements concentration have been analyzed by using a method of synchrotron radiation X-ray fluorescence (SRXRF).It provides a powerful analytical technique to detect most chemical elements of the periodic table down to limits of a few ppm.In this study,the fitted peak areas of elements Ti,Fe and Rb were normalized by the region of interest from 1946 to 1974 channels,while the fitted peak areas of elements Cu,Zn and Br were normalized by peak area of Compton scattering fitted.The Chinese national standard material GBW 07301a was used to control the analysis quality.The elements concentration in lake sediments have been regulated by many factors such as physical and chemical process,particle size,vegetation and so on.Bromine is a typical biogenic element,and is essential for growth of plants,bacteria and plankton.In lake sediments,bromine comes mainly from biogenic matter in soil and plankton in the lake.In order to understand the relationship between elements content and climate variable (temperature/precipitation),we comparatively studied the elements variation in Huguangyan Maar Lake and regional instrumental data.Bromine variation is positively correlated with instrumental precipitation.The increasing precipitation could transport more bromine from soil to sediment,as well as nutrition beneficially for algae and plankton production.Higher bromine values occur between 1200A.D.and 1600A.D.,while lower bromine values are during 800～ 1200A.D.and 1700～ 1900A.D.Spectral analysis of bromine content shows notable periodicities of 1.5,1.9～2.0,2.1 ～2.6 years at a confidence level ＞95％,2.9～3.0 years at a confidence level ＞90％,and 374～442 years at a confidence level ＞95％,221～256 years at a confidence level ＞80％.It may imply that bromine content variability for the past 1200 years could be associated with the El Ni（n）o-Southern Oscillation at yearly timescale,and solar activity at centennial timescale.Titanium content was positively correlated with precipitation roughly,implying that precipitation conducive to the depositing of element titanium.However,the density of vegetation cover and particle size may also have an important effect on the titanium value in lake sediments.
基金项目
国家自然科学基金面上项目(41302141)
国家自然科学基金面上项目(41371219和41274074)
中国地质调查局地质调查项目(1212011120045)
NETL
NSTL
维普
万方数据