TERRAPUB Geochemical Journal
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Geochemical Journal, Vol. 44 (No. 5), pp. 347-357, 2010

Testing seawater Sr isotopic variability on a glacial-interglacial timescale: An application of latest high-precision thermal ionization mass spectrometry

Atsushi Ando,1,2 Takanori Nakano,1 Hodaka Kawahata,3,4 Yusuke Yokoyama3,5 and Boo-Keun Khim2

1Research Institute for Humanity and Nature (RIHN), Motoyama 457-4, Kamigamo, Kita-ku, Kyoto 603-8047, Japan
2BK21 Coastal Environmental System School, Division of Earth Environmental System, Pusan National University, San 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea
3Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
4Graduate School of Frontier Sciences, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
5Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan

(Received September 21, 2009; Accepted January 4, 2010)

Abstract: Stability in seawater 87Sr/86Sr ratios over a glacial-interglacial timescale has gained the consensus, yet inter-site inconsistency exists in the previous data employed for validation of this issue. This study tests if the use of state-of-the-art Thermo FinniganTM TRITON multi-collector thermal ionization mass spectrometer (TIMS) can place more rigorous constraints on the seawater 87Sr/86Sr evolution at such a narrow timescale, by utilizing modern seawater, benthic foraminifera (150 ka-present) and corals (30 ka-present) (all sampled from the western Pacific realm). Application of a high-intensity setting (mass 88Sr beam at 20 V) with internal and external precisions of ±0.000005 (2 SE) and ±0.000006 (2 SD), respectively, generates remarkably consistent 150 ka record of seawater Sr isotopes, such that 94.4% of foraminiferal 87Sr/86Sr data fall within a ±0.000006 envelope relative to a regression function. Undoubtedly the 150 ka 87Sr/86Sr trend exhibits no short-term, orbitally-paced variation. Meanwhile, unlike previous inference, our 87Sr/86Sr record cannot be attributed to a simple linear function, implying that higher-order, minor (amplitude ≤0.000010) 87Sr/86Sr oscillation might have been present on the timescale greater than glacial-interglacial cycle. Our observations are demonstrative data-based verification and improvement upon previous knowledge of the glacial-interglacial seawater 87Sr/86Sr ratios. We emphasize that high-precision 87Sr/86Sr analysis with the TRITON TIMS certainly enables us to discriminate minute Sr isotopic details of (paleo-)oceanographic significance.
Key words: TIMS, Sr isotopes, seawater, glacial-interglacial cycle


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