稀土元素作为示踪标记在海洋沉积动力学中应用前景的初步探讨

A preliminary study on fingerprinting approach in marine sediment dynamics with the rare earth elements

根据对长江等5条河流和东海陆架区总计146个沉积物样品的稀土元素和粒度分析结果,借助统计学方法,讨论了河流和东海近岸沉积物稀土元素分布格局的形成因素及其对沉积动力作用的响应,结果表明,各河流沉积物在稀土元素总量和轻重稀土分异等参数上有差异;在长江口沉积物中稀土元素在小于2和2~31μm粒级中较富集,全岩稀土元素含量受物质组成占优的粒级控制;在东海陆架研究区稀土元素含量由岸向海有减小的趋势,在河口附近相对较高,轻重稀土分异自28°N向南有增大的趋势。

Total of 146 sediment samples were collected from the shelf of the East China Sea and five rivers,including the Huanghe River,the Changjiang River,the Qiantang River,the Oujiang River and the Minjiang River.The sediment grain-size and the content of rare earth element（REE） were measured with a laser particle size analyzer and an ICP-MS respectively.Results show that the REE absolute content and the ratio of LREE（light REE） to HREE（heavy REE） content are different in the sediments between rivers.There are higher REE contents in being less than 2 μm and 2~31 μm fractions in Changjiang Estuary surface sediments,and the bulk sediment REE contents are dominated by the corresponding values of those prevalent size-fractions.In the study area,the REE absolute contents of sediments are higher near the estuaries,and they trend downward in seaward direction on the inner shelf of the East China Sea.The ratio of LREE to HREE content has a tendency of increase southward from 28° N,whilst hydrodynamic conditions are dominated by the spacial distributions of the surficial sediment＇s REE parameters.In some cases,the current flows tend to remove the coarser light grains from initial populations,whilst deposit the finer heavy mineral grains.In most situations,the currents will change the ratio of sediment constituents,for example,between silts and clays.As a result,the various values of the REE absolute content or ratio of LREE to HREE content in different bulk sediments result from the change of size-fractions,rather than represent their different sources.Under the long-term stable hydrodynamic environment,i.e.,on the East China Sea shelf,a new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters.