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Theoretical and experimental investigation of nickel isotopic fractionation in species relevant to modern and ancient oceans |
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| Authors: | Toshiyuki Fujii,Fré dé ric Moynier,Minori Abe |
| Affiliation: | a Research Reactor Institute, Kyoto University, 2-1010 Asashiro Nishi, Kumatori, Sennan, Osaka 590-0494, Japan b Department of Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University in St. Louis, Campus Box 1169, 1 Brookings Drive, Saint Louis, MO 63130-4862, USA c Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA d Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji-shi, Tokyo 192-0397, Japan |
| Abstract: | Nickel plays a central role as an enzyme co-factor in the metabolism of methanogenic Archaea. Methanogens can fractionate Ni isotopes during assimilation, opening the possibility of using the stable isotopic composition of Ni as a biomarker. However, other sources of Ni isotopic variations need to be evaluated before one can establish Ni isotopes as an unambiguous tracer of methanogenesis in the rock record. Equilibrium exchange of Ni between the different species present in the ocean is a potential source of isotopic fractionation. Through controlled laboratory experiments and theoretical calculations, we quantify equilibrium Ni isotope fractionation between different species relevant to the modern and ancient ocean: Ni(H2O)62+, Ni(H2O)182+, NiOH(H2O)5+, Ni(OH)2(H2O)4, NiCl(H2O)5+, cis-NiCl2(H2O)4, trans-NiCl2(H2O)4, NiHS(H2O)5+, Ni(HS)2(H2O)4, NiSO4(H2O)4, NiHCO3(H2O)4+, NiCO3(H2O)4, and organic ligands (crown ether and oxalic acid). The magnitude of ligand-controlled Ni isotopic fractionation, approximately 1.25‰/amu (2.5‰ for the 60Ni/58Ni ratio), is similar to that previously measured in cultures of methanogenic Archaea. |
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