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Lecture 7: Back into the Icehouse: Last 55 Myr (Chapter 6)

Lecture 7: Back into the Icehouse: Last 55 Myr (Chapter 6). CO2 evolution in the last 50 Myr. Did climate cool?. Cooling inferred from terrestrial evidences. Antarctic. Arctic. Northern mid-lattiude cooling inferred from leave shape. 10-15 o C. Problem with land records: incomplete,

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Lecture 7: Back into the Icehouse: Last 55 Myr (Chapter 6)

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  1. Lecture 7: Back into the Icehouse: Last 55 Myr(Chapter 6)

  2. CO2 evolution in the last 50 Myr

  3. Did climate cool?

  4. Cooling inferred from terrestrial evidences Antarctic Arctic

  5. Northern mid-lattiude cooling inferred from leave shape 10-15oC Problem with land records: incomplete, sporadic, regional

  6. Abyssal Time Machine (continuous!) Cooling trend inferred from benthic foraminifera δ18O Paleothermometer Δδ18Oshell= Δδ18OW+ Δδ18OT i) Δδ18OT=ΔT/4.2oC Cooler (temperature dependence) increases ii) Δδ18OWMore continental ice increases Δδ18OW (fractionation)

  7. 18 18 18 0 ‰ d O + ‰ d O - ‰ d O 水样 Evaporation leads to fractionation Heavy molecular more stable standard (SMOW) heavy light Light isotope(16O) Heavy (minor) isotope (18O)

  8. -16 -14 -12 -10 -8 -6 -4 -2 Equilibrium Fractionation ‰d18O Isotope fractionation thermodynamicfractionation proportional to temperature

  9. δ18O fractionation Antarctica and Greenland all melting reduces Δδ18OW from 0  -1

  10. IAEA/WMO/GNIP Stations (183 stations in 53 countries)

  11. Long term mean seasonal cycle

  12. Abyssal Time Machine (continuous!) Cooling trend inferred from benthic foraminifera δ18O 13oC Δδ18OT =1.75 Δδ18OW =1.0 Δδ18Oc =2.75 Paleothermometer Δδ18Oshell= Δδ18OW+ Δδ18OT Δδ18OT =1.5, Δδ18OW =0 Δδ18Oc =1.5 i) Δδ18OT=ΔT/4.2oC Cooler (temperature dependence) increases ii) Δδ18OWMore continental ice increases Δδ18OW (fractionation)

  13. An independent paleothermometer: Ma/Ca

  14. Two independent paleothermometers=> ice sheet 15oC 13oC 14oC

  15. Abyssal Time Machine (continuous!) Cooling trend inferred from benthic foraminifera d18O Consistent evidence Deep ocean/high latitude cools by 15oC over 55 myr 1) Cooler (temperature dependence) 2) More continental ice (fractionation)

  16. Why does the climate cools?

  17. Ocean Gateway Hypotheses Hypothesis: Closing of Panama isthmus (10-4 myr) redirects warm/salty water northward, preventing sea ice formation, more evaporation to help glaciation Hypothesis:Opening of Drake’s Passage (20myr) cools the Antarctic

  18. Opening of Panama Isthmus Hypothesis: Closing of Panama isthmus (10-4 myr) redirects warm/salty water northward, preventing sea ice formation, more evaporation to help glaciation Problem: earlier by 2 myr for glacial cycle Modeling: opposite due to heat transport

  19. Drake Passage Hypothesis:Opening of Drake’s Passage (20myr) cools the Antarctic Problem: timing 10 myr before intense glaciation, 10 myr after first glaciation Modeling: not too much effect, Combined A+O heat transport not much change Lesson: needs to be more quantitative and comprehensive!

  20. Ocean Gateway Hypotheses Hypothesis: Closing of Panama isthmus (10-4 myr) redirects warm/salty water northward, preventing sea ice formation, more evaporation to help glaciation Problem: earlier by 2 myr for glacial cycle Modeling: opposite due to heat transport Contradictory to each other! Too much handwavering Hypothesis:Opening of Drake’s Passage (20myr) cools the Antarctic Problem: timing 10 myr before intense glaciation, 10 myr after first glaciation Modeling: not too much effect

  21. Why does the climate cools?The Role of CO2 Reduced CO2: Slower input (BLAG) Faster removal (uplifting weathering) Increased coastal upwelling buried enough organic carbon

  22. Testing spreading (BLAG) hypothesis No ?? OK

  23. Testing uplifting weathering hypothesis

  24. Tibetan Plateau the unusually large uplifting in the last 20 myr No major high topography like this in the last 150 myr

  25. Tibetan Plateau suspended particles, evidence of unusual physical weathering from Tibet

  26. Himalayan sediments in the Indian Ocean: Evidence of strong physical weathering • Steep terrain along the southern Himalaya • Uplift intensified monsoon (why?)

  27. Positive feedback on uplifting due to ice rock fragmentation Feedbacks on uplifting weathering Negative feedback on uplifting due to chemical weathering

  28. Asian monsoon References for ReadingTibet Uplift: Climate Impact An, Z., Kutzbach, J. Prell, W. & Porter, S., 2001: Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan plateau since Late Miocene times. Nature, 411, 62-66 Boos and Kuang, 2010: Dominant control of the South Asian monsoon by oragrphic insolation versus plateau heating. Science, 463, 218-222 Potential Impact on global thermohaline Emile-Geay J., et al., 2003: Warren revisited: Atmospheric freshwater fluxes and “Why is no deep water formed in the North Pacific”, Journal of Geophysical Research, Vol.108(C6), 3178, doi:10.1029/2001JC001058

  29. Early Pliocene Climate: An Analogue for Future Global Warming Climate? (move to later orbital…) Fedorov A. et al., 2006: The Pliocene Paradox (Mechanisms for a permanent El Nino). Science, 312, 1485-1489

  30. Tropical Pacific SST changes (Wara et al. 2005) 18O West East SST Strong gradient ∆SST Weak gradient

  31. End of Chapter 6

  32. Volcanic aerosol cooling

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