12. Greenhouse - Ante-pre show Pre-show Quadrophenia The...

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Ante-pre show
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Pre-show Quadrophenia The Cretaceous Chalk cliffs at Beachy Head, England
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12. Greenhouse sea-level and climate changes Earliest Oligocene = Transantarctic Mt. today Eocene Antarctica =Tasmania today Global sea level & δ 18O
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New National Research Council synthesis red = greenhouse Light blue = cool/glaciations Dark blue = bipolar icehouse
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New Phanerozoic summary
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Triassic to Eocene: Warm, generally ice free pole ca. 50 Ma (Eocene) fossil of an alligator Ellesmere Island ca. 90 Ma Champsosaur Arctic (Axel Heiberg Island) Ellesmere Island Eocene Metasequoia stumps Axel Heiberg Is. Ellesmere Island today 250-50 Ma Greenhouse
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Warm, generally ice free poles Early Jurassic Cryolophosaurus http://www.marshalls-art.com/pages/ppaleo/largepaleo/largepg11/Cryolophosaurus.htm ca. 100 Ma forest in Antarctica
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Mostly Ice free Mesozoic (250-65 Ma) ca. 180 Ma glaciation Siberia?
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Cretaceous Paleoclimate fossils indicate warm temperatues during the Mesozoic, particularly the Triassic and Late Cretaceous low equator-to-pole gradient (much lower than today) Why? Something was fundamentally different: Ice distribution, ocean circulation changes, CO2 levels, paleogeography?
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In 1982 Eric Barron and Warren Washington performed a series of experiments to evaluate possible climate forcing functions. To bring polar temperatures to 0°C means a global average increase of 4.5-6°C (from 15°C to19.5 or 21°C) Something else was needed Climate Model experiments Remove modern topography + 1.1°C Move continents to Cretaceous positions + 3.1°C Raise sea level to Cretaceous position -0.1°C Add Cretaceous topography - 1.1°C Net change + 3.8°C
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Royer et al., 2004 What about CO2? Increasing CO2 by a factor of 4 increased the global temperature 3.6°C
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However, there is no consensus on how high CO2 levels were in the Cretaceous 2-10 X Is it CO2?
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Clicker question What was the Cretaceous a greenhouse world? A) Mean temperatures 4-6°C above present B) High (2-10 X) CO2 C) Little to no ice sheets D) Warm high latitudes E) All of the above.
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Clicker question The extreme warmth of the Late Cretaceous “supergreenhouse” can be explained primarily by A) Changes in the position of continents B) High (2-10 X) CO2 C) High sea level D) Lower continental elevation E) All of the above.
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http://news.mongabay.com/2008/0306-sea_levels.html Continental flooding: eustasy or tectonics?
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Supercontinents mean super low sea level
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Greater ocean crust production raises sea level Exponential subsidence Mean age ocean crust 55 Ma…make it youger, it sits higher…
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Age of crust movie: Mueller’s group
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Depth of oceans
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High rates of seafloor spreading cause ridges to sit higher, flooding the continents on the 107 y scale: Tectonoeustasy Slow process produces < 10m/my sea-level change Kominz, 1984 Seafloor spreading + ridge length = ocean crust production and ocean basin size Error ranges on this curve.   These uncertainties are mainly due to uncertainties in  reconstructions and subducted lithosphere.
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Oceanic crust production high rate of oceanic crust production caused higher global sea level
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12. Greenhouse - Ante-pre show Pre-show Quadrophenia The...

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