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What causes ice ages to occur about every ~100,000 years?

What causes ice ages to occur about every ~100,000 years? Evidence for ice ages over the last 2.5 Myr Changes in ice volume and sea level What causes ice ages? Astronomical control of solar radiation Milankovitch theory: insolation control of ice sheets

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What causes ice ages to occur about every ~100,000 years?

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  1. What causes ice ages to occur • about every ~100,000 years? • Evidence for ice ages over the last 2.5 Myr • Changes in ice volume and sea level • What causes ice ages? • Astronomical control of solar radiation • Milankovitch theory: insolation control of ice sheets • The cycle of ice sheet growth and decay

  2. What causes ice ages to occur • about every ~100,000 years? Reading: • Ruddiman, W. F. (2008). Earth’s Climate: Past and Future. Key Chapter 9: 155 - 161, 163 - 168. For the astronomers and mathematicians ...... Chapter 7: 121 - 129. For the (oxygen) isotope geochemists ...... • Appendix 1: 359 - 361.

  3. Before we start ………. NOTE: Change of time for today’s practical: Start: 2 PM Finish: 4 PM Room needed for RSES 40th anniversary.

  4. How much did the earth cool over the last ~55 Myr?

  5. Polar ice caps increase the d18O of seawater

  6. Ice Ages Foraminiferal 18O evidence of ice sheet evolution over the last ~3 Myr

  7. Anatomy of an ice age Slow ice growth Rapid ice demise

  8. Raised coral reefs record sea level (Huon Peninsula, Papua New Guinea)

  9. March 2005 Nias earthquake, +2.5 m uplift

  10. Reef growth at lower seal level

  11. Tectonic uplift and preservation of coral reef

  12. Raised coral reefs record sea level (Huon Peninsula, Papua New Guinea)

  13. Ice sheets around the Arctic Ocean

  14. Solar radiation and ~100,000-year pacing of ice ages Maximum Minimum

  15. Changes in Earth’s orbit: The 23,000-year precession cycle

  16. Summary of climatic impacts of precession • Produces changes in seasonal distribution of insolation across Earth’s surface (not changes in total amount of insolation) • When NH summer occurs at perihelion (every 23 kyr): • Warmer summer / cooler winter in NH • Cooler summer / warmer winter in SH

  17. Changes in Earth’s orbit: The 23,000-year precession cycle (+ eccentricity)

  18. Precession (23 kyr) + eccentricity (100 kyr)

  19. Why do ice ages end so abruptly? Maximum Minimum

  20. Ice Ages The relationship between temperature and ice mass balance

  21. Ice Ages Orbital changes and ice sheet growth and decay

  22. Ice Ages Milankovitch theory: Orbital control of ice sheets

  23. Ice Ages Milankovitch theory: The relationship between changes in insolation and position of the ice sheet “equilibrium line”.

  24. The ice-elevation feedback

  25. Ice volume lags behind summer insolation

  26. Insolation changes and the cycle of ice sheet growth and decay

  27. What causes the end of an ice age? Maximum Minimum

  28. Deep-sea 18O record indicating relationship between ice volume and ice age “tipping points” Denton et al. (2010) Science

  29. Next time …… What is the relationship between ice ages and atmospheric greenhouse gases?

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