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Title: Determination of the tungsten isotope composition in seawater: The first vertical profile from the western North Pacific Ocean
Authors: Fujiwara, Yuta
Tsujisaka, Makoto
Takano, Shotaro
Sohrin, Yoshiki  kyouindb  KAKEN_id  orcid (unconfirmed)
Author's alias: 高野, 祥太朗
宗林, 由樹
Keywords: Tungsten isotope
Molybdenum isotope
Chemical separation
North Pacific Ocean
Issue Date: 20-Nov-2020
Publisher: Elsevier BV
Journal title: Chemical Geology
Volume: 555
Thesis number: 119835
Abstract: The stable isotope ratio of W is a new tracer in oceanographic studies and a new proxy in paleoceanographic studies; however, precise data for modern seawater have not been reported to date. Because the concentration of W in seawater is as low as 49 pmol kg⁻¹, an ~3000-fold preconcentration is necessary prior to measurement by multicollector inductivity coupled plasma mass spectrometry (MC-ICP-MS). For the preconcentration, we investigated solid-phase extraction using chelating resins, namely, NOBIAS Chelate-PA1 with ethylenediaminetriacetic acid groups and TSK-8HQ with 8-hydroxyquinolie groups. We report that TSK-8HQ is useful because the effects of the seawater matrix are minor thermodynamically and kinetically. We present a novel method for analysis of the concentrations and isotope ratios of W and Mo in seawater, consisting of solid phase extraction, chromatographic separation using anion exchange resin AG1 X8, and measurement by MC-ICP-MS. Both W and Mo are quantitatively recovered by this method, which was applied to seawater samples collected from the North Pacific Ocean. The measured concentration of W and the concentration and isotope ratio of Mo are consistent with those in the literature. The isotope ratio of W is found to be uniform throughout the water column in the western North Pacific Ocean; δ¹⁸⁶/¹⁸⁴W is 0.55 ± 0.12‰ (ave ± 2sd, n = 7) using NIST SRM 3163 as a reference for W. On the basis of this data, we determined that the isotopic difference in δ¹⁸⁶/¹⁸⁴W is ~0.49‰ between seawater and oxic sediments in the modern ocean. This value accords with the reported experimental data for the isotope fractionation of W during adsorption on manganese and iron (oxyhydr)oxides, suggesting the validity of our data.
Rights: © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
The full-text file will be made open to the public on 20 November 2022 in accordance with publisher's 'Terms and Conditions for Self-Archiving'.
This is not the published version. Please cite only the published version. この論文は出版社版でありません。引用の際には出版社版をご確認ご利用ください。
DOI(Published Version): 10.1016/j.chemgeo.2020.119835
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