13_neogene - Cenozoic Cooling Polar position no CO2...

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Cenozoic Cooling Polar position – no • CO 2 Sources- not a perfect fit Sinks- Uplift hypothesis (intriguing) Controversial Gateways Intriguing correlations, but timing difficult to pinpoint
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Cenozoic Cooling Discussed overall trend Look at shorter-term events Mi-1 Mid Miocene Climate Optimum Miocene transition Late Miocene carbon shift Mid Mio Clim Opt Mio Transition Zachos et al., 2007 Oi1 Mi1
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Neogene Climate Miocene Cool to warm climate optima to cooling. Intervals of ice growth (and decay) throughout Miller et al., 1991
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Neogene Climate Zachos et al., 2001 Miller et al., 1992 Olig – mid Mio = warming interrupted by cooling event Zachos et al., 2007 Mi1
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Neogene Pagani et al., 2005 Boron- Pearson and Palmer, 2000 Alkenone- Pagani et al., 1999
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Zachos et al., 2002 1. Shift in δ 18 O and δ 13 C 1. δ 13 C amplitude response to 400 ky 2. δ 13 C and δ 18 O amplitude response to 400 ky 1. Both phase locked with 400 ky cycle 2. Climate more responsive at low PCO 2 (21.7 – 23 my) 3. Carbon paced by forcing, feeds back to climate system 4. Mi1 = convergence of Obliq node and Eccent min Mi1
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Mi1 Equatorial Atlantic Site Zachos et al., Science, 2002 Obliquity node (22.8 to 23.7° ) and Eccentricity min. = Sustained low seasonal variability Compared to rest of record δ 18 O minimum and baseline shift (full scale ice + a few degrees cooling) δ 13 C shift “cause unknown.” Increased burial of organic carbon Impacts climate sensitivity Shift in climate mode with brief overshoot
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Mi1 Pagani et al., 1999 P CO2 from alkenones Decrease across Oligocene/Miocene *
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Mid Miocene Climatic Optima Zachos et al., 2001 Zachos et al., 2007
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Mid Miocene Climate Optima ~17 – 14 Ma General expansion of tropical flora and fauna Up to 6° warming in midlatitudes Corals on North Island, New Zealand and in Japan (~35-40°) Crocodiles in S.D.
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Monterey Excursion ~ +1 per mil global shift in δ 13 C Associated with organic carbon-rich deposits Circum Pacific Monterey Fm SE US Hawthorne Fm Berger and Mayer, 1987 Cooling lags C burial
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Monterey Hypothesis Increased ocean circulation increased meridional gradients Stronger winds Increased upwelling Increased productivity (phosphate deposits) Increased organic carbon burial • Drawdown atmospheric CO 2 Cooling
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This document was uploaded on 07/08/2011.

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13_neogene - Cenozoic Cooling Polar position no CO2...

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