Sulfur Isotopes and the Evolution of the Atmosphere

The atmosphere has changed drastically over Earth’s 4.6 billion year lifespan. Anomalous patterns among the isotopes of sulfur hold great promise for providing insight into the evolution of atmospheric chemistry on both Earth and Mars. The enigmatic signals known as sulfur mass-independent isotope fractionation (S-MIF) are seen in aerosol particles in the stratosphere, within ice core sulfates, in Martian meteorites, as well as among the most ancient sedimentary rocks on the planet, with ages of up to 3.8 billion years old. It is remarkable that this unique signature generated by the photolysis of SO2 (Farquhar 2001) remains preserved in the rock record, providing us an indirect record of ancient atmospheric chemistry. In particular, the presence of S-MIF is a defining signature of sedimentary rocks laid down prior to Earth’s great oxidation, which occurred approximately 2.4 billion years ago. Subtle variations in the magnitude of S-MIF may reflect changes in the concentrations of CO2, biogenic sulfur compounds, and the presence of a Titan-like organic haze during periods of Earth history (Ueno, 2009 ; Halevy, 2010 ; Claire, 2010 ; Zerkle, 2011). Understanding how the signature is formed, transported, deposited, and stored, will enable us to constrain the composition and structure of the paleo atmosphere. This project will primarily involve numerical modelling of atmospheric chemistry, specifically using a 1-D photochemical model enhanced to study the 4 isotopes of sulfur. The model will be validated against geochemical data from Earth system environments, and applied to the study of sulfate aerosols in the modern atmosphere as well as constrain atmospheric chemistry before Earth’s great oxidation. With sufficient student interest, the project could also include field work and/or measuring carbon and sulfur isotopes with an interdisciplinary and international team of researchers.

Applications are processed as soon as they are received, so early application is encouraged. NB applicants who wish to start their studies in October 2012 should submit their application by 31 July 2012. Applications received after this date will be considered for the January 2013 entry point if the project is still available.