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10_cenozoic-orbital - Cenozoic Record of global cooling...

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Cenozoic Record of global cooling Transition from: Cretaceous Warmth (no ice or small ephemeral ice sheets) to Pleistocene (ice caps in both hemispheres)
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Cenozoic Time Scale 1.8 Ma 5.3 Ma 23.8 Ma 33.6 Ma 65 Ma 54.8 Ma Zachos et al., 2001
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Cenozoic Cooling Stepwise cooling of high latitudes and deep waters Recorded by oxygen isotopes Record of global ice volume and temperature
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δ 18 O δ 18 O to temperature T = 16.9 – 4.38( δ c δ w ) + 0.10 ( δ c δ w ) 2 (Shackleton, 1974) δ c = δ 18 O in foram calcite δ w = δ 18 O in seawater (varies with ice volume)
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δ 18 O Record of the Cenozoic Isolating the ice volume effect Shackleton (mid 1970s) Bottom waters stayed cool during glacial/interglacials, near freezing Assume benthic record = ice volume Both planktic and benthic change = ice volume Unequal change = temperature
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Shackleton and Kennett (1975) Savin (1977) SubAntarctic Pacific About 50 data points
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δ 18 O Isolating the ice volume effect Prentice and Matthews (1988) Change in benthic δ 18 O values larger than those of corals, tropical planktonics- includes a temperature component as well (Cretaceous warm bottom water) Total change in benthics greater than change anticipated from ice free to bipolar ice sheets Equatorial surface waters changed little (or predictably) with glaciations (CLIMAP, isotopes data), thus equatorial planktonics record ice volume
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ice volume = equatorial Planktic record deep to surface gradient = Benthic – planktic Implied: Ice free until 50 Ma Extensive intervals of WSBW All data adjusted to western tropical Pacific Cooling of deep waters Paleocene Eocene Oligocene Miocene Plio
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Cenozoic Record Miller et al., 1987 and Zachos et al., 2001 Improved data sets New ways to view the record
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