title: Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse.
abstract: The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals - at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ(13)C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE.
authors.affiliation: Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark.|Department of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, Sweden.|Center for Macroecology, Evolution and Climate, University of Copenhagen.
authors.forename: Christian M Ø
authors.initials: CM
authors.lastname: Rasmussen
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark.|Camborne School of Mines, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, U.K.
authors.forename: Clemens V
authors.initials: CV
authors.lastname: Ullmann
authors.affiliation: Ministry of Mineral Resources, Maneq 1A, 201, P.O. Box 930, 3900 Nuuk, Greenland.
authors.forename: Kristian G
authors.initials: KG
authors.lastname: Jakobsen
authors.affiliation: Department of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Lindskog
authors.affiliation: Akvaplan-Niva, High North Research Centre 9296 Tromsø, Norway.
authors.forename: Jesper
authors.initials: J
authors.lastname: Hansen
authors.affiliation: Akvaplan-Niva, High North Research Centre 9296 Tromsø, Norway.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hansen
authors.affiliation: Department of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, Sweden.
authors.forename: Mats E
authors.initials: ME
authors.lastname: Eriksson
authors.affiliation: Geological Institute of the Russian Academy of Sciences, Moscow, Russian Federation.
authors.forename: Andrei
authors.initials: A
authors.lastname: Dronov
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark.|Nordic Center for Earth Evolution (NordCEE), University of Copenhagen.
authors.forename: Robert
authors.initials: R
authors.lastname: Frei
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark.
authors.forename: Christoph
authors.initials: C
authors.lastname: Korte
authors.affiliation: Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark.
authors.forename: Arne T
authors.initials: AT
authors.lastname: Nielsen
authors.affiliation: Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK.
authors.forename: David A T
authors.initials: DA
authors.lastname: Harper
mesh_terms: D059001:Aquatic Organisms; D044822:Biodiversity; D017753:Ecosystem; D008962:Models, Theoretical; D011827:Radiation