日本地球惑星科学連合2019年大会

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[J] ポスター発表

セッション記号 M (領域外・複数領域) » M-TT 計測技術・研究手法

[M-TT48] 地球化学の最前線

2019年5月26日(日) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:角野 浩史(東京大学大学院総合文化研究科広域科学専攻相関基礎科学系)、横山 哲也(東京工業大学理学院地球惑星科学系)、小畑 元(東京大学大気海洋研究所海洋化学部門海洋無機化学分野)

[MTT48-P02] Determination of picomolar of zirconium, hafnium, niobium and tantalum in seawater using chelating resin and subsequent ICP-MS determination

*小畑 元1Lutfi Firdaus2真塩 麻彩実3金 泰辰4Jason McAlister5蒲生 俊敬1 (1.東京大学大気海洋研究所海洋化学部門海洋無機化学分野、2.ブンクル大学、3.金沢大学理工学部、4.ソウル国立大学、5.ブリティッシュコロンビア大学)

キーワード:Zr, Hf, Nb and Ta、high field strength elements、海水

It has been known that Zr, Hf, Nb and Ta are high field strength elements (HFSE) belonging to group IV and V in the periodic table. Among these elements, Zr-Hf and Nb-Ta are geochemical twin elements who have similar chemical properties (i.e., ionic charge and radius) in crustal materials and rocks. Contrastingly, the ratios of Zr/Hf and Nb/Ta in seawater are strongly fractionated, and can be used as chemical tracers for the movement of water masses in the modern ocean and as a proxy for paleo-ocean circulation (Firdaus et al., 2011; Frank, 2011). However, for example, the average Zr concentration is 250 pmol/kg in deep seawater, which is more than 6 order of magnitude lower than those in rock materials. It is still challenging for us to determine sub-picomolar to picomolar of HFSE in seawater.

In this study, we developed a simple method to determine sub-picomolar to picomolar of dissolved Zr, Hf, Nb and Ta in seawater using chelating resin column preconcentration and ICP-MS. With mini-columns filled with commercially available chelating resin, HFSE were preconcentrated by 50 times. We obtained low blank values and good recovery enough to determine HFSE in open ocean surface waters. The detection limits, calculated from the procedural blank values, were 0.15 pmol/kg for Zr, 0.03 pmol/kg for Hf, 0.06 pmol/kg for Nb and 0.03 pmol/kg for Ta, respectively.

Using the new method, we revealed distributions of Zr, Hf, Nb and Ta in open ocean, the North Pacific Ocean, North Atlantic Ocean, Indian Ocean and in the marginal sea, Andaman Sea and Gulf of Thailand. We will discuss the fractionations of Zr–Hf and Nb–Ta in the marine environments.