Astrobiology Workshop, Macquarie University July 12-13 2001

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Fractionations of Fe and Mo Isotopes: Measurements and Models

Ariel Anbar (University of Rochester, Dept. of Earth & Environmental Sciences)

Because of recent analytical advances in geochemistry, particularly the development of multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), it is now possible to measure variations in the isotopic composition of transition metals to a precision of better than one part per thousand (e.g., 1 - 4). At this level of precision, significant natural variations in the isotopic compositions of all these metals are apparent, as are variations of similar magnitude produced by both biological and nonbiological chemical processes in the laboratory (1, 2, 4, 5). The potential use of such variations as "biosignatures" for the study of ancient biological processes is under active investigation by researchers in the NAI (e.g., 2, 5, 7).

Mechanistic studies in progress indicate that chemical speciation in solution and reaction kinetics are important influences on the direction and magnitude of metal isotope fractionation (e.g., 2, 7, 8). Modeling studies predict substantial fractionation effects between dissolved Fe species at equilibrium (9). These findings suggest that study of such isotope fractionations could provide new tools to study mechanisms of metal metabolism, with potential applications in biomedicine.

This poster will provide an overview of MC-ICP-MS methods and performance obtained at the University of Rochester for Fe and Mo, along with a summary of findings from our initial studies of biological and nonbiological laboratory systems, and natural materials. Fractionation predictions based on vibrational modeling will also be presented.

References:

1. Marechal C. N., Telouk P., and Albarede F. (1999) Chem, Geol. 156, 251-273.

2. Anbar A. D., Roe J. E., Barling J., and Nealson K. H. (2000) Science 288, 126-128.

3. Belshaw N. S., Zhu X.-K., Guo Y. and O^ÒNions R. K. (2000) Int. J. Mass. Spectr. 197, 191-195.

4. Anbar A. D., Knab K. A., and Barling J. (2001) Anal. Chem. 73, 1425-1431.

5. Beard B. L., Johnson C. M., Cox L., Sun H., Nealson K. H., and Aguilar C. (1999) Science 285, 1889-1892.

6. Zhu X.-K., O'Nions K., Guo Y., and Reynolds B. C. (2000) Science 287, 2000-2002.

7. Brantley S. L., Liermann L., Wu S., and Bullen T. D. (1999) EOS Trans. AGU 80, 479.

8. Bullen T. D., McMahon P. B., Mandernack K. W., Bazylinski D. A., Childs C. W., and White A. F. (1999) EOS Trans. AGU 80, 479.

9. Schauble E., Taylor H. P., and Rossman G. R. (2001) Geochim. Cosmochim. Acta, in press.