HR: 0800h
AN: U31A-0017    [Abstracts]
TI: Sulfur Mass Independent Fractionation in the Oxidizing Atmosphere?
AU: * Mills, M J
EM: mills@colorado.edu
AF: LASP, University of Colorado, 392 UCB, Boulder, CO 80303-0392 United States
AU: Pavlov, A A
EM: alex.pavlov@lasp.colorado.edu
AF: LASP, University of Colorado, 392 UCB, Boulder, CO 80303-0392 United States
AU: Toon, O B
EM: brian.toon@lasp.colorado.edu
AF: LASP, University of Colorado, 392 UCB, Boulder, CO 80303-0392 United States
AB: The discovery of mass-independent fractionation (MIF) in sulfur isotopes in Archean sediments and a lack of MIF in sulfur in the younger rocks (Farquhar, 2000) places a strict upper constraint on the amount of oxidants and oxygen in the ancient atmosphere prior to 2.3 Gyr ago (Pavlov and Kasting, 2002). However recent Antarctic ice core measurements show a small, but non-zero, MIF in sulfate correlated with the large volcanic eruptions (Savarino et al., 2003). Moreover, recent measurements of isotopic compositions in present-day sulfate aerosols also exhibit non-zero MIF (Romero and Thiemens, 2003). MIF must be produced by UV photolysis in the stratosphere or mesosphere, but sulfur re-entering the troposphere takes only one chemical form (sulfate), making preservation of any sulfur MIF signature difficult to explain. We added sulfur isotopes to the Garcia-Solomon 2D dynamical/chemical model with aerosol microphysics and looked at how strong the initial atmospheric fractionation has to be in order to be preserved upon descent to the troposphere. Our calculations can quantitatively constrain the oxidative capacity of the atmosphere over the period of the ice core record. We will discuss two possibilities to preserve small sulfur MIF in the present atmosphere: 1) Preservation through stratospheric and mesospheric sulfate aerosols 2) Preservation through the alternative pathway of SO2 oxidation (Savarino et al., 2003).
DE: 3344 Paleoclimatology
DE: 1040 Isotopic composition/chemistry
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0325 Evolution of the atmosphere
DE: 0370 Volcanic effects (8409)
SC: Union [U]
MN: 2004 AGU Fall Meeting