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Chapter 10 — Insolation control of ice sheets

Explore the factors that control the size of ice sheets, including elevation, latitude, and insolation. Learn about the Milankovitch theory and its implications for ice sheet size. Discover how ice sheet behavior can be modeled and understand the feedback mechanisms involved. Examine the historical evidence for ice sheet evolution through δ18O and sea level indicators.

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Chapter 10 — Insolation control of ice sheets

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  1. Chapter 10— Insolation control of ice sheets Ruitang Soong

  2. Outline • What controls the size of ice sheet? • Modeling the behavior of ice sheets • North hemisphere ice sheet history

  3. What controls the sizeof ice sheet? • Elevation & Latitude • Temperate • Insolation • Orbit of Solar-Earth Figure 10-1

  4. Orbital-scale control of ice sheet:The Milankovitch theory • Key point Summer insolation control of ice sheets • Previous study J.A. Adhemar (1842) James Croll (1864, 1875) Milutin Milankovitch (1915~ 1940) combined precession, eccentricity, and tilt. Chose summer in the northern high latitudes as the important season; predicted warm periods at 125, 105, and 82 ka.

  5. Diagram depicting variation in precession. Image by Robert Simmon, NASA GSFC. Taken from http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch.html. 

  6. Figure 10-2 Figure 10-3

  7. Modeling the behavior of ice sheets • weak insolation in summer Ice growth, ice & bedrock depression • strong insolation in summer Ice melting, ice slipping & calving, bedrock swelling • Two feedback mechanism

  8. Insolation Control of ice sheet size • Climate point • Equilibrium line Figure 10-5

  9. Figure 10-7 Figure 10-6

  10. Ice sheet lags behind summer insolation forcing Ice volume response to lnsolation Figure 10-8

  11. Figure 10-9

  12. Delayed bedrock response beneath ice sheet • Elastic response • Viscous response Tack from: Richard E. Goodman, Introduction to Rock Mechanics, 2/e, 1989,Wiley Figure 10-10

  13. Figure 10-11 Bedrock feedback to ice growth and melting Insolation control of ice sheet size the initial lag of ice volume behind insolation the subsequent lag of bedrock depression and rebound behind ice loading and unloading

  14. Full cycle of ice growth and decay Figure 10-12

  15. Ice slipping and calving • Basal slipping (terrain, stress) • Calving • Ice sheet models can be coupled to 3D GCM models.

  16. North hemisphereice sheet history

  17. Conceptual Model: Evolution of ice sheet cycles • Changes in summer insolation (shorter-term change) • Gradual global cooling (longer-term change) Note: cycle of tilt is 41,000 year cycle of precession is 23,000 year cycle of eccentricity is 100,000 and 413,000 year Figure 10-13

  18. Figure 10-14

  19. Evidence from δ18O:How ice sheets actually evolved • Ocean sediments contain two key indicator of past glaciations Ice-rafted debris δ18O N. Shackleton Figure 10-15

  20. Figure 10-16 Figure 10-17

  21. Confirming ice volume change:Coral reefs and sea level • δ18O (ice volume) • Radiocarbon (234U→230Th) • Ice-rafted debris • Coral reefs (sea level)

  22. Box 10-3

  23. Using astronomical and δ18O signals as a chronometer • Orbital tuning Figure 10-21

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