Geochemical cycles of platinum group elements at the earth surface -Role of anthropogenic and cosmic sources-

本文的研究成果总结如下。建立了测定固体样品中铂族元素丰度的高精度、高灵敏度方法。采用同位素稀释法(Ru、Pd、Os、Ir、Pt)和外校正法(仅用于Rh)，结合火焰试金预富集技术，建立了测定固体样品中铂族元素丰度的高精度、高灵敏度方法。我们将这种方法应用于日本地质调查局(GSJ)发布的JP-1标准岩石。PGE的误差范围为13-25%(2s；n=5)，与同类方法结合化学分离PGE的结果相当。将我们的数据与GSJ提出的较好的数据进行比较，发现IR有很大的偏差。各种证据表明，我们的数据比可取值可靠得多。为阐明元素在海洋中的水平迁移过程，我测定了西北太平洋4个测站和西北太平洋表层海水的Nd同位素组成的垂直分布。这些结果表明，ND参与了表层海洋(100-250m以上)活跃的水平输送过程。海水中Sc丰度的高灵敏度测定方法的建立及其在海洋化学中的应用为了测试Sc作为陆源物质进入海洋的可能指示物，我们建立了海水中Sc丰度的高灵敏度测定方法。夏威夷群岛附近空间站的垂直剖面显示为所谓的“营养型”，类似于Y和稀土元素。

My research results are summarized as follows.1. Development of high precision and sensitivity method for determining abundances of platinum group elements in solid samples.I have developed high precision and sensitivity method for determining abundances of platinum group elements (PGE : Ru, Rh, Pd, Os, Ir and Pt) in solid samples by isotope dilution method (for Ru, Pd, Os, Ir and Pt) and external calibration method (only for Rh) using ICP-MS combined with a fire assay preconcentration technique. We applied this method to a standard rock JP-1 issued from the Geological survey of Japan (GSJ). The errors of PGE range 13-25%(2s ; n=5), which are comparable with those by the similar methods combined with chemical separation of PGE. Compared our data with the preferable data proposed by GSJ, the large deviations are observed for Ir. Various evidences indicate that our data are much more reliable than the preferable value.2. Educidation of horizontal transport processes of elements in ocean using the Nd isotopic compositions of seawatersTo elucidate the horizontal transport processes of elements in ocean, I determined the vertical distribution of Nd isotopic compositions at four stations in the Northwest Pacific together with that of surface seawaters at the Northwest Pacific. These results suggest that Nd is involved in the active horizontal transport processes in the surface ocean (above 100-250m).3. Development of high sensitivity method for determining abundances of scandium (Sc) in seawater and its application to marine chemistryTo test Sc as a possible indicator of continentally derived material to the ocean, we developed of high sensitivity method for determining abundances of Sc in seawater. The vertical profile at the station near the Hawaii Islands showed so called "nutrient type" one, which was similar with Y and lanthanides.