Le Geotop - Dr. Huy Dang: Uranium Isotopic Biogeochemistry... (16-02-2018)

Dr. Huy Dang: Uranium Isotopic Biogeochemistry... (16-02-2018)

 

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Dr. Huy Dang, School of the Environment, Trent University

Uranium Isotopic Biogeochemistry and Applications as an Environmental and Paleoenvironmental Proxy

Vendredi 16 février 2018 à 15h30 / Friday, February 16, 2018, 3:30 pm

Redpath Museum Auditorium, 859 Rue Sherbrooke O, Université McGill

Résumé / Abstract :

D. Huy Danga, Cedric Garnierb, R. Douglas Evansc

a School of the Environment, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada
b Université de Toulon, Aix Marseille Université, CNRS, IRD, Mediterranean Institute of Oceanography (MIO), UMR7294, 83041 Toulon Cedex 9, France
c Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, ON K9L 0G2, Canada

Despite reservations of general public about the uses of uranium, this heaviest naturally occurring element on Earth has particular characteristics that interest geochemists. A major area of research is to track biogeochemical mechanisms that control U cycling and consequently reconstruction of depositional conditions, e.g., seawater chemistry and/or oxygenation history of Ancient Earth. In fact, as a redox-sensitive element, accumulation of authigenic U can be used to track redox boundaries1 as well as any oxidative disturbances (e.g., oxygenation penetration) in the depositional environment2. In addition, recent advances in analytical techniques have revealed uranium isotope fractionation, which was previously assumed insignificant given the small difference in mass between U isotopes (ca. 1%)3.

Using U isotope composition for paleoenvironmental studies is possible because of U isotope fractionation, where there is an enrichment of the light isotope (235U) on adsorbent surfaces (e.g., Fe and Mn oxides) and accumulation of the heavy isotope (238U) in reductive fractions3. More interestingly, the intensity of U isotope fractionation is variable, either in an oxic or anoxic environment. In the oxic environment when U is incorporated into CaCO3 4 or adsorbed on Mn/Fe oxides3, δ238U varies according to U aqueous speciation (free UO22+ vs. uranyl carbonate vs. organic U). However, in an anoxic environment (e.g., marine sediments), variations in δ238U seem to be driven by U diffusion from seawater and have been used as an indicator for terrestrial material delivery via river5.

Finally, the mechanisms controlling U cycling and fractionation between U isotopes have been examined in an Ontario lake contaminated by U tailings, together with microbial functional gene quantification and molecular analysis of the bioavailable organic matter6. These approaches have supported potential applications of U isotope composition in deciphering the major mechanisms of U biogeochemistry and as an environmental and paleoenvironmental proxy.

References:
(1) Tribovillard, N.; Algeo, T. J.; Lyons, T.; Riboulleau, A. Chem. Geol. 2006, 232 (1–2), 12–32.
(2) McManus, J.; Berelson, W. M.; Klinkhammer, G. P.; Hammond, D. E.; Holm, C. Geochim. Cosmochim. Acta 2005, 69 (1), 95–108.
(3) Dang, D. H.; Novotnik, B.; Wang, W.; Georg, R. B.; Evans, D. Environ. Sci. Technol. 2016, 50, 12695–12704.
(4) Chen, X.; Romaniello, S. J.; Anbar, A. D. Geochim. Cosmochim. Acta 2017, 215, 162–172.
(5) Dang, D. H.; Evans, R. D.; Wang, W.; Omanović, D.; Houssainy, A. El; Lenoble, V.; Mullot, J.; Mounier, S.; Garnier, C. Chem. Geol. 2018, In Press.
(6) Dang, D. H.; Wang, W.; Pelletier, P.; Poulain, A. J.; Evans, D. Sci. Total Environ. 2018, 610–611, 880–891.