Senior Marine Scientist, Dauphin Island Sea Lab
Ph.D. 2013, Department of Geology, University of Illinois at Urbana-Champaign
Emphasis: Marine Geochemistry, Redox Reactions, Metal Isotopes
Why reduction-oxidation (redox for short) reaction is important:
Redox reactions are the main means for life to extract energy from the environment. A central player in redox reactions is molecular oxygen. The ambient level of oxygen determines the types of ecosystems: anaerobic vs. aerobic. For instance, low oxygen conditions in seawater can lead to “dead zones” we see today, or mass extinctions that occurred in the geological past. Therefore, knowledge about the evolution of oxygen level in the ocean is critical for understanding the coevolution of life and environment.
Why redox-sensitive metal isotope systems are important?
Measuring the oxygen content in the modern ocean is simply a matter of deploying a set of sensors. Measuring oxygen level in the paleocean, however, is tricky. We have to turn to marine sediments as a historical book to estimate what oxygen level was like in the overlying water column. Fortunately, some redox-sensitive metals are well suited for this application. For instance, chromium (Cr) is isotopically fractionated (i.e. 53Cr/52Cr ratio is shifted) during reduction/oxidation reactions, and the isotopic ratio is then preserved in sediments.
Redox-sensitive metal isotope systems as redox proxies have been introduced into our geochemical toolbox only since ten years ago, largely due to analytical constraint. However, the advent of modern mass spectrometers allows measurement of isotopic ratios at sub-tenth of a permil. This precise measurement allows us to detect small isotopic shifts induced by redox reactions. However, such small isotopic shifts could easily be overprinted by non-redox reactions during deposition, or by later diagenetic alterations. Therefore, there is great need for work designed to understand the basic fractionation mechanisms during uptake from seawater and during early diagenesis, since this knowledge is essential for correctly interpreting metal isotope signals recorded in sedimentary rocks. And this is an important part of my research.
Saad E.M., Wang X.L., Planavsky N.J., Reinhard C.T., Tang Y. Accepted. Chromium isotope fractionation induced by ligand-promoted mobilization of Cr(III)-containing mineral.
Tarhan L.G., Planavsky N.J., Wang X.L., Bellefroid E., Droser M.L. and Gehling J.G. Accepted. The Late-Stage ‘Ferruginization’ of the Ediacara Member (Rawnsley Quartzite, South Australia): Insights from Uranium Isotopes. Geobiology.
Cole D.B., Wang X.L., Qin L., Planavsky N.J. 2017. Chromium isotopes geochemistry. In Earth Science Series – Encyclopedia of Geochemistry.
Wu W.H., Wang X.L., Reinhard C.T., Planavsky N.J. 2017. Chromium isotope systematics in the Connecticut River. Chemical Geology. Vol. 456, p. 98-111.
Qin L.P., Wang X.L. 2017. Chromium isotope geochemistry. In: Teng F.Z., Watkins J.M., and Dauphas N. (Eds.), Measurements, Theories and Application of Non Traditional Stable Isotopes. Reviews in Mineralogy and Geochemistry. Vol. 82, p. 379-408.See More
Hood A., Planavsky N.J., Wallace M.W., Wang X. L., Bellefroid E.J., Gueguen B. and Cole D.B. 2016. Integrated geochemical-petrographic insights from component-selective δ238U of Cryogenian marine carbonates. Geology. Vol. 44, p. 935-938.
Wang X.L., Planavsky N.J., Hull P., Tripati A., Zou H., Henehan M.J., Elder L. 2016. Chromium isotopic composition of core-top planktonic foraminifera. Geobiology. DOI: 10.1111/gbi.12.
Cole D., Gueguen B., Wang X., Reinhard C., Halverson G., Lyons T., Planavsky N. 2016. A shale-hosted Cr isotope record of low atmospheric oxygen during the Proterozoic. Geology. G37787.
Gueguen B., Reinhard C., Algeo T., Nielsen L.P.S., Wang X., Planavsky N. 2016. The chromium isotope composition of reducing and oxic marine sediments. Geochimica et Cosmochimica Acta. vol. 184, p. 1-19.
Wang X. L., Planavsky N.J., Reinhard C.T., Hein J.R., Johnson T.M. 2016. A Cenozoic seawater redox record derived from 238U/235U in ferromanganese crusts. American Journal of Science. vol. 316, p. 64–83.
Wang X. L., Reinhard C.T., Planavsky N.J., Johnson T.M. 2016. Sedimentary chromium isotopic compositions across the Cretaceous OAE2 at Demerara Rise Site 1258. Chemical Geology. vol. 429, p. 85–92.
Wang X. L., Planavsky N.J., Reinhard C.T., Zou H., Ague J., Wu Y., Peucker-Ehrenbrink B. 2016. Chromium isotope fractionation during subduction-related metamorphism, black shale weathering and hydrothermal alteration. Chemical Geology. vol. 423, p. 19-33.
Wang X. L., Johnson T.M., Lundstrom C.C. 2015. Isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen. Geochimica et Cosmochimica Acta. vol. 150, p. 160-170.
Wang X. L., Johnson T.M., Ellis A.S. 2015. Equilibrium isotopic fractionation and isotopic exchange kinetics between Cr(III) and Cr(VI). Geochimica et Cosmochimica Acta. vol. 153, p. 72-90.
Wang X. L., Johnson T.M., Lundstrom C.C. 2015. Low Temperature Equilibrium Isotope Fractionation and Isotope Exchange Kinetics between U(IV) and U(VI). Geochimica et Cosmochimica Acta. vol. 158, p. 262-275.
Planavsky N.P., Reinhard C.T., Wang X. L., Thomason D., McGoldrick P., Rainbird R.T., Johnson T.M., Fischer W.W., Lyons T.W. 2014. Low mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals. Science. vol. 346, p. 635-638.
Reinhard C.T., Planavsky N.J., Wang X. L., Fischer W.W., Johnson T.M., Lyons T.W. 2014. The isotopic composition of authigenic chromium in anoxic marine sediments and controls on the chromium isotope composition of seawater. Earth and Planetary Science Letter. vol. 407, p. 9-18.
Planavsky N.J., Asael D., Hofmann A., Reinhard C.T., Lalonde S.V., Knudsen A., Wang X. L., Ossa Ossa F., Pecoits E., Smith A.J.B., Beukes N.J., Bekker A., Johnson T.M., Konhauser K.O., Lyons T.W., Rouxel O.J. 2014. Evidence for Oxygenic Photosynthesis Half a Billion Years Before the Great Oxidation Event, Nature Geoscience. vol. 7, p. 283-286.
Xie X., Johnson T.W., Wang Y., Lundstrom C.C., Ellis A.S., Wang X. L., Duan M., Li J. 2014. Pathways of arsenic from sediments to groundwater in the hyporheic zone: Evidence from an iron isotope study. Journal of Hydrology. vol. 511, p. 509-517.
Wang Y., Xie X., Johnson T.M., Lundstrom C.C., Ellis A.S., Wang X. L., Duan M., Li, J. 2014. Coupled iron, sulfur, and carbon isotope evidences for arsenic enrichment in groundwater. Journal of Hydrology. vol. 519, p. 414-422.
Zhu J., Johnson T.M., Clark S.K., Zhu X., Wang X. L. 2013. Selenium redox cycling during weathering of Se-rich shales: A selenium isotope study. Geochimica et Cosmochimica Acta. vol. 126, p. 228-249.
Xie X., Johnson T.M., Wang Y., Lundstrom C.C., Ellis A.S., Wang X. L., Duan M. 2013. Mobilization of arsenic in aquifers from Datong Basin, China: Evidence from geochemical and iron isotopic data. Chemosphere. vol. 90, p. 1878-1884.