海洋沉积物的铁和锌同位素测定

介绍海洋沉积物Fe和Zn同位素化学前处理及测定方法,报道南海西部夏季上升流区两个沉积物柱样的Fe和Zn同位素组成。样品采用HF+HNO3+HClO4常压消解,经脱盐后,转化为氯化物形式并经离子交换柱分离纯化后,用多接收器等离子体质谱法测定Fe和Zn同位素比值。该前处理方法可以快捷地实现海洋沉积物的消解、有机质的去除和海盐脱离;结合相关测试流程,可获得较高的δ56Fe(0.10‰,2SD)和δ66Zn分析精度(0.11‰,2SD)。两个沉积物柱样的δ56Fe值(相对于IRMM-014)和δ66Zn值(相对于JMC3-0749C)随深度变化不明显,两柱之间也无明显差异。总体上,南海西部上升流区1～2 ka以来的沉积物δ56Fe值(0.04‰～0.20‰)和δ66Zn值(0.12‰～0.30‰)与已报道的黄土和气溶胶、火成岩以及大部分海洋沉积物接近,明显高于静海相海洋沉积物的δ56Fe值。

High-precision measurements of Fe and Zn isotopic ratios in marine sediments

We present an optimized chemical separation and purification procedure as well as an analytical method for measuring Fe and Zn isotopic composition in marine sediments. We also report Fe and Zn isotopic compositions in two sediment cores with an age of 1-2 ka from the summer upwelling region in the western South China Sea. Samples were dissolved with an acid solution （HF ＋ HNO3 ＋ HClO4） under normal pressure, followed by desalination and transformation to chloride matrix. After separation and purification, Fe and Zn isotopic ratios were determined with a Nu Plasma HR MC-ICPMS. Results demonstrate that this chemical preparation can rapidly dissolve marine sediments, remove organic matter, and, in combination with this analytical technique, we achieved high analytical precisions of 0.10‰ for δ56Fe （2SD） and of 0.11‰ for δ66Zn （2SD）. These two sediment cores had nearly invariant δ56Fe and δ66Zn values throughout the sediment cores. Moreover, δ56Fe （0.04‰ - 0.20‰） and δ66Zn （0.12‰ - 0.30‰） from these 1-2 ka marine sediments are overall close to those reported for loesses and aerosols, igneous rocks and other marine sediments worldwide, but much higher than those deposited in euxinic environments.