High-precision zirconium isotope analysis of Pacific seawater reveals large mass-dependent fractionations in the ocean
High-precision zirconium isotope analysis of Pacific seawater reveals large mass-dependent fractionations in the ocean
复制标题
DOI：
10.1016/j.gca.2023.11.018
复制
发表时间：
2023-11
影响因子：
5
通讯作者：
Linqing Huang;F. Tissot;M. Ibáñez-Mejia;K. Forsch;Carli Arendt;C. Anela Choy;Sarah M. Aarons
中科院分区：
文献类型：
--
作者：
Linqing Huang;F. Tissot;M. Ibáñez-Mejia;K. Forsch;Carli Arendt;C. Anela Choy;Sarah M. Aarons
锆（Zr）稳定同位素最近成为岩浆过程的潜在示踪剂，因此，它们在高温环境中的行为一直是广泛表征的焦点。相比之下，很少有研究关注低温或水环境中锆的行为和同位素分馏。在这里，我们描述了一种新的分析程序，结合使用双尖峰和铁共沉淀方法，对水样中的 Zr 同位素进行高精度和准确的分析。为了评估潜在系统偏差的影响，对天然和合成水样进行了一系列实验。我们的结果表明，加标与样品的比率、基质成分和高场强元素 (HFSE) 浓度对测量的海水 Zr 同位素成分的影响可以忽略不计，并且使用 Fe 共沉淀方法可以得到准确且精确的 Zr 同位素数据。因此，我们将该方法应用于从加利福尼亚州海岸附近的太平洋水柱剖面采集的天然海水样本，深度范围为 5 至 711 m。我们发现，天然海水样品相对于固体地球值高度分馏，并且随着深度的变化，δ94/90Zr 显示出显着的变化，范围从接近地表的 ~ +0.650 ‰ 到接近剖面底部的 +1.530 ‰，分析不确定度为 ± ∼0.045 ‰（2 SE，外部再现性）。海水的 δ94/90Zr 值远高于地幔和大陆地壳的 δ94/90Zr 值，后者的 δ94/90Zr 值接近于零，表明水圈中存在能够引起大量依赖于质量的分馏的过程。此外，海水δ94/90Zr值随水深和盐度表现出系统变化，表明Zr同位素组成可能对海水化学性质和来源敏感，突出了其作为海洋内生物地球化学过程示踪剂的潜在用途。
Zirconium (Zr) stable isotopes recently emerged as potential tracers of magmatic processes and, as a result, their behavior in high-temperature environments have been the focus of extensive characterization. In contrast, few studies have focused on Zr behavior and isotopic fractionation in low temperature or aqueous environments. Here, we describe a new analytical routine for highly precise and accurate analysis of Zr isotopes of water samples, using a combination of double-spike and iron co-precipitation methods. To assess the impact of potential systematic biases a series of experiments were conducted on natural and synthetic water samples. Our results show that the spike-to-sample ratio, matrix composition, and high field-strength element (HFSE) concentration have negligible effects on measured seawater Zr isotopic compositions, and that the Fe co-precipitation method used yields to accurate and precise Zr isotope data. We thus apply this method to natural seawater samples collected from a water column profile in the Pacific Ocean off the coast of California, with depths ranging from 5 to 711 m. We find that the natural seawater samples are highly fractionated relative to solid-Earth values and display marked variability in δ94/90Zr as a function of depth, ranging from ∼ +0.650 ‰ near the surface, to +1.530 ‰ near the profile bottom, with an analytical uncertainty of ± ∼0.045 ‰ (2 SE, external reproducibility). The δ94/90Zr value of seawater is much higher than that of Earth’s mantle and continental crust, which has a δ94/90Zr value near zero, indicating the presence of processes in the hydrosphere capable of inducing large mass-dependent fractionation. Furthermore, the seawater δ94/90Zr value exhibits systematic variations with respect to water depth and salinity, suggesting that Zr isotopic compositions may be sensitive to seawater chemical properties and source highlighting its potential utility as a tracer of biogeochemical processes within the ocean.