Title: Sensitivity of Oxygen Isotopes of Sulfate in Ice Cores to Past Changes in Atmospheric Oxidant Concentrations
Author: Sofen, E.D., Alexander, B., Kunasek, S.A., Mickley, L., Murray, L.T. and Kaplan, J.O.
Periodical: American Geophysical Union, Fall Meeting 2009, abstract #B13D-0545
Abstract: The oxygen isotopic composition ( Δ 17O) of sulfate from ice cores allows for a quantitative assessment of the past oxidative capacity of the atmosphere, which has implications for the lifetime of pollutants (e.g. CO) and greenhouse gases (e.g. CH4), and changes in the sulfur budget on various timescales. Using Δ 17O of sulfate measurements from the WAIS-Divide, Antarctica and Site-A, Greenland ice cores as constraints, we use the GEOS-Chem global three-dimensional chemical transport model to study changes in the concentrations of OH, O3, and H2O2 and their impact on sulfate Δ 17O between the preindustrial and present-day. The Greenland ice core sulfate oxygen isotope observations are insensitive to changes in oxidant concentrations on the preindustrial-industrial timescale due to the rising importance of metal catalyzed S(IV) oxidation in mid- to high-northern latitudes resulting from anthropogenic metal emissions. The small change in Antarctic ice core sulfate Δ 17O observations on this timescale is consistent with simultaneous increases in boundary layer O3 (32%) and H2O2 (49%) concentrations in the Southern Hemisphere, which have opposing effects on the sulfate O-isotope anomaly. Sulfate Δ 17O is insensitive to the relatively small (-12%) decrease in Southern Hemisphere OH concentrations on this timescale due to the dominance of in-cloud versus gas-phase formation of sulfate in the mid-to-high southern latitudes. We find that the fraction of sulfate formed globally through gas-phase oxidation has not changed substantially between preindustrial and present times, however the total amount of sulfate formed in the gas-phase has nearly quadrupled due to rising anthropogenic emissions of sulfur dioxide. Measurements over a glacial-interglacial cycle from the Vostok core indicate dramatic changes in the Δ 17O of sulfate on this timescale, which provide a strong constraint for glacial-era atmospheric chemistry modeling efforts. We will present preliminary results of sulfate Δ 17O from glacial-era simulations using offline-coupled GISS ModelE, BIOME4, and GEOS-Chem models.
Year: 2009