title: Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse.
abstract: Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO(2) (8 to 22x PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan ("mixed layer") marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55 degrees -70 degrees S to approximately 40 degrees S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO(2) from a modeled Sandbian level of approximately 8x PAL to approximately 5x PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction.
authors.affiliation: Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, United Kingdom. Thijs.vandenbroucke@univ-lille1.fr
authors.forename: Thijs R A
authors.initials: TR
authors.lastname: Vandenbroucke
authors.forename: Howard A
authors.initials: HA
authors.lastname: Armstrong
authors.forename: Mark
authors.initials: M
authors.lastname: Williams
authors.forename: Florentin
authors.initials: F
authors.lastname: Paris
authors.forename: Jan A
authors.initials: JA
authors.lastname: Zalasiewicz
authors.forename: Koen
authors.initials: K
authors.lastname: Sabbe
authors.forename: Jaak
authors.initials: J
authors.lastname: Nõlvak
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Challands
authors.forename: Jacques
authors.initials: J
authors.lastname: Verniers
authors.forename: Thomas
authors.initials: T
authors.lastname: Servais
mesh_terms: D000818:Animals; D001272:Atmosphere / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D002980:Climate; D017753:Ecosystem; D053476:Extinction, Biological; D049690:History, Ancient; D046448:Ice Cover; D013696:Temperature; D015048:Zooplankton
chemical_list: D002245:Carbon Dioxide