Nd isotope composition of fossil fish teeth of ODP Hole 119-738B

We report an optimized method for extracting neodymium (Nd) from fossil fish teeth with a single-stage column (125 µl stem volume; LN Resin, Eichrom Industries, Darien Illinois) for isotopic analysis by multi-collector inductively coupled mass spectrometry (MC-ICMPS). Three reference materials (basalt: BCR-2, BHVO-2; phosphate: fossil bone composite) and splits of fossil fish teeth samples previously processed with existing two-stage column methods were processed using the single-stage column method. 143Nd/144Nd values of reference materials agree within error with published values, and the values for fish teeth correspond with sample splits processed with two-stage columns. Precision to ± ~0.23 epsilon-Nd was achieved for 30 ng Nd samples of reference materials, and Nd isotope measurements of fossil fish tooth sample replicates as small as 7 ng Nd were reproducible within long term instrumental uncertainty. We demonstrate the utility of the new method with the first high resolution Nd isotope record spanning the ~40.0 Ma middle Eocene Climatic Optimum, which shows an excursion of 0.65 epsilon-Nd during the peak warming at the study site (Ocean Drilling Program Leg 119, Site 738; 30 kyr sample spacing from 40.3 to 39.6 Ma). LN Resin is already used in standard methods for separating Nd, and Nd isotopes are routinely measured by MC-ICPMS with high efficiency inlet systems. Our innovation is a single, small volume LN Resin column for Nd separation. The streamlined approach results in a 10X increase in sample throughput.

本研究报道了一种适配多接收器电感耦合等离子体质谱（multi-collector inductively coupled mass spectrometry，MC-ICPMS）同位素分析的优化方法，可从化石鱼齿中提取钕（Nd）：该方法采用单级色谱柱（柱床体积125 µL；LN树脂（LN Resin），艾希罗姆工业公司，伊利诺伊州达里恩）。本研究利用该单级色谱柱方法，处理了三类参考物质（玄武岩标样：BCR-2、BHVO-2；磷酸盐标样：化石骨复合标准物质），以及此前采用现有两级色谱柱方法制备的化石鱼齿样品平行样。结果显示，参考物质的143Nd/144Nd比值与已发表数据在误差范围内一致，鱼齿样品的同位素比值也与两级色谱柱处理的平行样结果相符。对于30 ng钕的参考物质样品，其测量精度可达±~0.23 εNd；而对于仅需7 ng钕的化石鱼齿平行样，其钕同位素测量结果在长期仪器不确定度范围内可重复。本研究通过首个覆盖约40.0 Ma始新世中期气候最佳期的高分辨率钕同位素记录，验证了新方法的实用性：该记录在研究站位（大洋钻探计划119航次738站位；40.3~39.6 Ma期间采样间距为30 kyr）的升温峰值期出现了0.65 εNd的偏移。LN树脂已被应用于钕分离的标准方法中，钕同位素通常可通过配备高效进样系统的MC-ICPMS进行常规测量。本研究的创新之处在于采用单根小体积LN树脂色谱柱完成钕分离，这一简化流程将样品处理通量提升了10倍。