title: Impact winter and the Cretaceous/Tertiary extinctions:  results of a Chicxulub asteroid impact model.
abstract: The Chicxulub impact crater in Mexico is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary.  2-D hydrocode modeling of the impact, coupled with studies of the impact site geology, indicate that between 0.4 and 7.0 x 10(17) g of sulfur were vaporized by the impact into anhydrite target rocks.  A small portion of the sulfur was released as SO3 or SO4, which converted rapidly into H2SO4 aerosol and fell as acid rain.  A radiative transfer model, coupled with a model of coagulation indicates that the aerosol prolonged the initial blackout period caused by impact dust only if the aerosol contained impurities.  A larger portion of sulfur was released as SO2, which converted to aerosol slowly, due to the rate-limiting oxidation of SO2.  Our radiative transfer calculations, combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20% of normal for a period of 8-13 yr.  This reduction produced a climate forcing (cooling) of -300 Wm-2, which far exceeded the +8 Wm-2 greenhouse warming, caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures.  Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2.  The prolonged impact winter may have been a major cause of the K/T extinctions.
authors.affiliation: Geo Eco Arc Research, La Canada, CA 91011, USA.
authors.forename: K O
authors.initials: KO
authors.lastname: Pope
authors.forename: K H
authors.initials: KH
authors.lastname: Baines
authors.forename: A C
authors.initials: AC
authors.lastname: Ocampo
authors.forename: B A
authors.initials: BA
authors.lastname: Ivanov
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D001272:Atmosphere; D005075:Biological Evolution; D002245:Carbon Dioxide; D004391:Dust; D019419:Evolution, Planetary; D019015:Geologic Sediments; D055593:Geological Phenomena; D005844:Geology; D017752:Greenhouse Effect; D008800:Mexico; D018543:Minor Planets; D008956:Models, Chemical; D010163:Paleontology; D013458:Sulfur Dioxide / Q000737:chemistry; D013461:Sulfur Oxides / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry
chemical_list: D000336:Aerosols; D004391:Dust; D013461:Sulfur Oxides; D013464:Sulfuric Acids; D013458:Sulfur Dioxide; D002245:Carbon Dioxide; C011118:sulfur trioxide