title: Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice.
abstract: An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65 million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70 kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 +/- 5 kilotons per year of meteoric smoke during the Holocene.
authors.affiliation: Laboratoire de Glaciologie et Géophysique de l'Environnement (UMR CNRS/ Université Joseph Fourier 5183), 54, rue Molière, BP 96, 38402 St Martin d'Heres cedex, France.
authors.forename: Paolo
authors.initials: P
authors.lastname: Gabrielli
authors.forename: Carlo
authors.initials: C
authors.lastname: Barbante
authors.forename: John M C
authors.initials: JM
authors.lastname: Plane
authors.forename: Anita
authors.initials: A
authors.lastname: Varga
authors.forename: Sungmin
authors.initials: S
authors.lastname: Hong
authors.forename: Giulio
authors.initials: G
authors.lastname: Cozzi
authors.forename: Vania
authors.initials: V
authors.lastname: Gaspari
authors.forename: Frédéric A M
authors.initials: FA
authors.lastname: Planchon
authors.forename: Warren
authors.initials: W
authors.lastname: Cairns
authors.forename: Christophe
authors.initials: C
authors.lastname: Ferrari
authors.forename: Paul
authors.initials: P
authors.lastname: Crutzen
authors.forename: Paolo
authors.initials: P
authors.lastname: Cescon
authors.forename: Claude F
authors.initials: CF
authors.lastname: Boutron