HR: 09:45h
AN: PP41D-08    [Abstracts]
TI: Mystery of the Volcanic Mass-independent Sulfur Isotope Fractionation Signature in the Antarctic Ice-core.
AU: * Pavlov, A A
EM: pavlov@lasp.colorado.edu
AF: Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Duane Physics Building, 392 UCB, Boulder, CO 80309-0392 United States
AU: Mills, M J
EM: mills@colorado.edu
AF: Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Duane Physics Building, 392 UCB, Boulder, CO 80309-0392 United States
AU: Toon, O B
EM: btoon@lasp.colorado.edu
AF: Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Duane Physics Building, 392 UCB, Boulder, CO 80309-0392 United States
AB: We provide the first quantitative explanation for the observed record of sulfur mass-independent fractionation (MIF) in the Antarctic sulfates from the 1991 eruption of Mt. Pinatubo (Savarino et al., 2003). Discovery of MIF in sulfur isotopes in the Archean/Early Proterozoic sediments and lack of MIF in sulfur in the younger rocks placed a strict upper constraint on the amount of oxidants and oxygen in the ancient Earth's atmosphere prior to 2.3 Gyr ago (Pavlov & Kasting, 2002). However, recent measurements in ice cores suggest that some non-zero MIF in sulfate can be delivered to Antarctica following large volcanic eruptions (Savarino et al., 2003). Current photochemical experiments do not identify the specific reaction responsible for sulfur MIF production. Here we show that a time-dependent non-zero sulfur MIF can be delivered to the ground in the present atmosphere if the primary MIF producing process is SO3 photolysis. We show that sulfur MIF signature is dependent on the magnitude of volcanic eruption (Pavlov et al., 2005) as well as on the volcano's location and the season of eruption. Our results would provide a quantitative constraint on how frequent and dramatic volcanic eruptions were in the past and where they should have occurred. References: Pavlov, A. A., and J. F. Kasting (2002), Mass-independent fractionation of sulfur isotopes in archean sediments: strong evidence for an anoxic atmosphere, Astropbiology, 2, 27-41. Pavlov, A. A., M. J. Mills, and O. B. Toon (2005a), Mystery of the volcanic mass-independent sulfur isotope fractionation signature in the Antarctic ice-core, Geophysical Research Letters, 10.1029/2005GL022784. Savarino, J., A. Romero, J. Cole-Dai, S. Bekki, and M. H. Thiemens (2003), UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate, Geophysical Research Letters, doi:10.1029/2003GL018134.
DE: 0370 Volcanic effects (8409)
DE: 4904 Atmospheric transport and circulation
DE: 4906 Aerosols (0305, 4801)
DE: 4932 Ice cores (0724)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005