Global Average Potassium Isotope Composition of Modern Seawater,ACS Earth and Space Chemistry

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Global Average Potassium Isotope Composition of Modern Seawater
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-06-19 , DOI: 10.1021/acsearthspacechem.0c00047
Kun Wang ₁ , Hilary G. Close ₂ , Brenna Tuller-Ross ₁ , Heng Chen _{1,

3}

Affiliation

The potassium isotope system was proposed as a new tracer in continental weathering and global K cycling. The largest K isotope fractionation observed among major reservoirs is between the ocean and bulk silicate Earth (BSE). Seawater is significantly enriched in heavy isotopes compared to BSE, and seawater represents the heaviest reservoir on Earth. Because of limited analyses, it is still unknown whether seawater is homogeneous in terms of K isotopes vertically, laterally, and globally. In addition, what processes (e.g., hydrothermal inputs) and to what degrees these processes have contributed to this heavy isotope enrichment in seawater are still not well constrained. To better understand the K isotopic compositions of modern seawater and to examine the possible influence of seafloor hydrothermal vents on the K isotope composition of seawater, we analyzed the K isotope composition of 46 seawater samples collected as two pairs of depth profiles in two locations from the Atlantic and Pacific oceans, including one near an active hydrothermal vent field (ASHES, Axial Seamount, Juan de Fuca Ridge). We found that within the current analytical uncertainty, all seawater samples have the same K isotope composition regardless of their location, depth, [K] concentration, and salinity. Combining our new analyses with data from previous studies, we define the best representative K isotope composition of modern seawater as +0.12 ± 0.07‰ (2SD). The seawater is significantly higher (0.55 ± 0.18‰) than BSE, which requires large K isotopic fractionation during continental weathering and reverse weathering.

中文翻译：

现代海水的全球平均钾同位素组成

钾同位素系统被提议作为大陆风化和全球钾循环的新示踪剂。在主要储层中观察到的最大的K同位素分馏是在海洋和大块硅酸盐地球（BSE）之间。与疯牛病相比，海水中的重同位素含量显着丰富，海水是地球上最重的水库。由于有限的分析，从垂直，横向和全局的K同位素角度来看，海水是否均匀是未知的。此外，还没有很好地限制什么过程（例如，热液输入）以及这些过程在多大程度上促进了海水中这种同位素的浓集。为了更好地了解现代海水的K同位素组成并研究海底热液喷口对海水K同位素组成的可能影响，我们分析了46个海水样品的K同位素组成，这些样品是在大西洋和太平洋的两个位置（包括一个活跃的热液喷口场（ASHES，轴向海山，胡安·德富卡海岭）附近的两个位置，以两对深度剖面收集的）组成的。我们发现，在当前的分析不确定性范围内，所有海水样品的K同位素组成均相同，无论其位置，深度，[K]浓度和盐度如何。将我们的新分析结果与以前的研究结果相结合，我们将现代海水中最具代表性的K同位素组成定义为+0.12±0.07‰（2SD）。海水比疯牛病高得多（0.55±0.18‰），在大陆风化和逆风化过程中，海水需要大量的K同位素分馏。

更新日期：2020-07-16

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