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Goals for this section

Quiz 5: Nov 30-Dec 1. Long-Term Climate Evolution:. Goals for this section. EXPLAIN the feedback mechanism believed to have maintained Earth's average temperature within the range of liquid water over 100s of millions of years, as the Sun got brighter.

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Goals for this section

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  1. Quiz 5: Nov 30-Dec 1 Long-Term Climate Evolution: Goals for this section • EXPLAIN the feedback mechanism believed to have maintained Earth's average temperature within the range of liquid water over 100s of millions of years, as the Sun got brighter. • Based on albedo, solar radiation, and atmospheric gases, CONSTRUCT logical chains of events that would result in major glaciations or warm periods on Earth. • IDENTIFY and EXPLAIN the primary trends and climate events of the past 65 million years based on oxygen isotope data. Final review is Dec 4: Submit Qs on Discussion Board

  2. RELEVANCE

  3. What next? More ICE WARM WARM 800-600 million years ago – Snowball Earth 2.5-2.3 billion years ago – Huronian glaciations 4.5 billion years ago – Earth forms SNOWBALL EARTH

  4. Evidence for Snowball Earth Ice in Australia, which was then at the equator

  5. Clicker Question: How could having all continents bundled near the equator help trigger a global glaciation? • The continents must have had high mountains where glaciers could form • Warm temperatures in the tropics would keep silicate weathering rates high • There would be less volcanism if all the continents were in the tropics • The poles could freeze more easily if they were water-covered • All of the above

  6. Getting into Snowball Earth Continents at low latitudes   chem weathering   CO2  colder Hoffman & Schrag Ice expansion  albedo  runaway ice-albedo feedback  SNOWBALL

  7. Clicker question: What’s the most likely factor to help Earth escape from the “snowball” scenario? • Increased burial of organic carbon (e.g. coal deposits) • Increased solar output • Lower sea level • Volcanic activity • Biological production of oxygen

  8. Escape from Snowball Earth Tectonics & volcanism   CO2 Ice cover prevents chem weathering   CO2 even more…  greenhouse finally gets strong enough to melt ice  ice-albedo feedback Hoffman & Schrag

  9. Clicker question: Once the ice sheets starting melting, more land surface was exposed. What kind of feedback loop between ice and albedo would be triggered as the Earth came out of the Snowball scenario? • Positive feedback loop • Negative feedback loop • Neither • Both

  10. Warm again, cold again… WARM WARM WARM 2.5-2.3 billion years ago – Huronian glaciations 800-600 million years ago – Snowball Earth 4.5 billion years ago – Earth forms 300-270 million years ago – Permo-Carboniferous glaciations

  11. Clicker question: The Permo-Carboniferous glaciations happened when all the continents were together in the supercontinent Pangaea. What effect would the process of assembling a supercontinent have on greenhouse gas concentrations? Greenhouse gases would ______. • Increase • Decrease • Stay the same

  12. Causes of the P-C glaciations Decreased atmospheric CO2 as Pangaea formed COLD!

  13. Causes of the P-C glaciations Formation of coal deposits

  14. ICE Ice cover during the P-C glaciations COAL DEPOSITS

  15. Clicker question: Why didn’t the Earth turn into a snowball this time? • As the continental ice sheets grew, sea level fell. • Glaciers excavated the new swamp deposits. • Ice cover on polar continents decreased silicate weathering. • Swamps output additional oxygen.

  16. Warm again, cold again, warm again… WARM WARM WARM WARM 2.5-2.3 billion years ago – Huronian glaciations 800-600 million years ago – Snowball Earth 4.5 billion years ago – Earth forms 300-270 million years ago – Permo-Carboniferous glaciations

  17. Causes of the post-glacial warming Pangaea was breaking apart Higher rates of seafloor spreadingIncreased CO2 from volcanoes

  18. Finally, the past 65 million years WARM WARM WARM WARM 2.5-2.3 billion years ago – Huronian glaciations 800-600 million years ago – Snowball Earth 300-270 million years ago – Permo-Carboniferous glaciations Last 2.5 million years – Pleistocene glaciations 4.5 billion years ago – Earth forms X LOW“Temperature”HIGH No more dinos! 70 60 50 40 30 20 10 0 Million years ago

  19. Warming prior to 50 Ma Subduction of carbon-rich sediments under Asia Warming LOW“Temperature”HIGH 70 60 50 40 30 20 10 0 Million years ago

  20. Cooling after 50 Ma Collision produced mountains and increased chemical weathering Long-term cooling LOW“Temperature”HIGH 70 60 50 40 30 20 10 0 Million years ago

  21. Estimating past temperatures For an ICE-FREE WORLD Ocean d18O Sediments Deep ocean temperature Benthic Forams: CaCO3

  22. Distillation of water  Fractionation of oxygen isotopes H216O (light) & H218O (heavy) ? ? H216O H216O H218O H216O H216O H216O

  23. Clicker Q: How would the oxygen isotopic composition of the water in an ice sheet compare to the oxygen isotopic composition of ocean water during an ice age? ? • Ice would be heavier than ocean • Ice would be lighter than ocean • Ice would be the same as ocean ?

  24. Evidence: Distillation of water  Fractionation of oxygen isotopes 16O (light) & 18O (heavy) • Sea level • Ice sheet size 16O “lighter” H216O H216O H216O H218O 18O “heavier”

  25. [ ] 18O/16Osample * 1000 -1 d18O = 18O/16Ostandard Foraminifera: CaCO3 CaC16O16O16O lighter CaC16O16O18O heavier CaC16O18O18O Temperature or 18O in the ocean  18O in the shells  18O/16O measured in shells Higher d18O  colder water temperatures (and/or more ice) Lower d18O  warmer water temperatures (and/or less ice)

  26. Estimates of past temperatures

  27. Who’s driving? Total “forcing” based on temperature estimates Changes in solar radiation and albedo Changes in greenhouse gases Pleistocene Glaciations

  28. Causes of the Pleistocene glaciations: India-Asia collision – decreased greenhouse Ice-albedo feedbacks once ice formed on Antarctica

  29. Summary: Long-term Climate Evolution • The “faint young Sun” paradox can be resolved by higher greenhouse gas concentrations in Earth’s early atmosphere. • Each of the 4 major glacial periods in Earth’s history occurred under different circumstances with different perturbations and feedbacks (construct the logical chains of events for each): • Huronian – rise of atmospheric oxygen, drawing down methane • Snowball Earth – continents in tropics, high weathering rates, ice-albedo feedbacks • Permo-Carboniferous – mountain building and organic carbon burial • Pleistocene – mountain building (Himalayas), then ice- albedo feedbacks • Oxygen isotope records from the past 65 My record temperature changes that help resolve the three main climate driving forces in this period – the Sun, albedo, and greenhouse.

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