Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 9, issue 11
Biogeosciences, 9, 4353–4367, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Coastal hypoxia and anoxia: a multi-tiered, holistic...

Biogeosciences, 9, 4353–4367, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Nov 2012

Research article | 08 Nov 2012

Variation in stable carbon and oxygen isotopes of individual benthic foraminifera: tracers for quantifying the magnitude of isotopic disequilibrium

T. Ishimura1,2,*, U. Tsunogai2,3, S. Hasegawa4, F. Nakagawa2, T. Oi4,**, H. Kitazato5, H. Suga5, and T. Toyofuku5 T. Ishimura et al.
  • 1Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
  • 2Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan
  • 3Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 4Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan
  • 5Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
  • *currently at: Department of Chemistry and Material Engineering, Ibaraki National College of Technology, Hitachinaka, Japan
  • **currently at: Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan

Abstract. Stable carbon and oxygen isotopic compositions (δ13C and δ18O) of benthic foraminiferal carbonate shells have been used to reconstruct past bottom-water environments. However, the details of factors controlling the isotopic disequilibrium between the shells and the surrounding bottom seawater (so-called the "vital effect") are still ambiguous. In this study, we analyzed the isotopic composition of individual benthic foraminifera of multiple species by using a customized high-precision analytical system, and found that the magnitude of the isotopic disequilibrium between benthic foraminiferal shell and the surrounding bottom seawater (δ13CDIC and δ18Owater) in different species is correlated with inter-individual isotopic variations. As a result, we can choose suitable species as bottom-water proxies by using the inter-individual isotopic variations. In addition, by using the simplified interpretation of the inter-individual and inter-species isotopic variations established in this study, we could reconstruct the δ13C values of dissolved inorganic carbon in bottom water by correcting foraminiferal isotopic compositions for the isotopic shift resulting from the isotopic effects (vital effect, microhabitat effect, and many other reported isotopic effects). Our findings will allow the use of isotope data for benthic foraminifera as more reliable proxies for reconstructing past bottom-water conditions and evaluating global carbon cycling.

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