title: Isotopic evidence for glaciation during the Cretaceous supergreenhouse.
abstract: The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35 degrees C. High-amplitude sea-level changes and positive delta18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New delta18O data from the tropical Atlantic show synchronous shifts approximately 91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.
authors.affiliation: Scripps Institution of Oceanography, University of California, San Diego, Geosciences Research Division, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA. a.bornemann@uni-leipzig.de
authors.forename: André
authors.initials: A
authors.lastname: Bornemann
authors.forename: Richard D
authors.initials: RD
authors.lastname: Norris
authors.forename: Oliver
authors.initials: O
authors.lastname: Friedrich
authors.forename: Britta
authors.initials: B
authors.lastname: Beckmann
authors.forename: Stefan
authors.initials: S
authors.lastname: Schouten
authors.forename: Jaap S Sinninghe
authors.initials: JS
authors.lastname: Damsté
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vogel
authors.forename: Peter
authors.initials: P
authors.lastname: Hofmann
authors.forename: Thomas
authors.initials: T
authors.lastname: Wagner