1 / 32

Lecture 10: Orbital Control of Ice Sheets

This lecture explores how orbital factors influence the growth and decay of ice sheets, with a focus on the Last Glacial Maximum and the role of insolation forcing. Topics include Milankovitch theory, ice-albedo feedback, thermal inertia, and sea level reconstructions.

mariabaker
Download Presentation

Lecture 10: Orbital Control of Ice Sheets

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 10: Orbital Control of Ice Sheets (Chapter 9)

  2. Ice sheet cover at 20,000 years ago The Last Glacial Maximum (LGM)

  3. Ice-sheet balance Slow Accumulation vs. fast Ablation Annual mean temperature Implication: which season is most important for ice sheet? Winter vs. summer

  4. Milankovitch theory Small tilt +Aphelion =>low summer insolation favor glaciation Large tilt + Perihelion => High summer insolation favor deglaciation

  5. Milankovitch theory High summer insolation => net melting => deglaciation Low summer insolation => net accumulation => glaciation

  6. The Last Glacial Maximum (LGM): 21,000 yrs ago Why the greatest ice sheet not over Siberia?

  7. How does Insolation Control Ice Sheet Equilibrium line, Climate point and ice-sheet formation Cold Warm

  8. High insolation • northern/high equilibrium line • northern climate point • less ice-sheet formation • Low insolation • southern/low equilibrium line • southern climate point • more ice-sheet formation

  9. Two positive feedbacks Ice-albedo feedback Ice-elevation feedback

  10. Thermal inertial and Phase lag Ice volume lags insolation mdT/dt = SeiΩt-bT

  11. Phase lag Ice volume lags Insolation by about ¼ cycle (ocean effect on seasonal cycle!)

  12. Bedrock sinking Bedrock sinking and Bedrock rebound

  13. Bedrock feedbacks Bedrock feedbacks: Initial elastic response is negative feedback; Later viscous response is positive feedback relative to the elastic sinking response by producing a delayed sinking response

  14. The cycle of ice-sheet growth and decay

  15. Conceptual model for ice-sheet cycle: • Repeat constant insolation • Threshold temperature: 0oC summer, -10oC annual mean

  16. Deep sea 18O and ice volume history 18O ~ O18/O16 O16 light, easy to evaporate Deep sea higher 18O  more ice volume over land (evaporated to be accumulated)

  17. Quantify δ18O changes Δ (18Oland*land ice volume)+ Δ( 18Oocean*ocean volume)=0 18Oland* Δ land ice volume + Δ 18Oocean*ocean volume=0 1/(-40) = 18Oocean/ 18Oland =-Δ land ice volume / ocean volume = -100m sl/4000m sl = -1/40

  18. Deep sea 18O and ice volume history ~1o/oo Large glaciation phase Small glaciation phase

  19. Revival of Milankovith Theory 1976 but, relative magnitude ?

  20. Insolation Forcing and Ice Volume Response Small glaciation phase Large glaciation phase The remaining question: 100 kyr cycle?

  21. Ice sheet 18O in the last 150,000 years Dominant 100 kyr cycle, why? 0 ka: Interglacial 21 ka: Last Glacial Maximum 125 ka: Last interglacial

  22. Ice Core 18O in the last 100,000 years is it ice volume effect?

  23. Confirming sea level change Coral reefs lives in coastal water – a proxy of sea level

  24. Uplifted coral reef terraces: New Guinea (western Pacific)

  25. Uplift of coral reefs: Quantifying the ice volume from the sea level change -110m (115ka) to +6m (125ka)

  26. Sea Level Reconstruction of the last 30 kyr LGM IPCC/AR4 2007

  27. References for Further reading and analysis • Hays et al., 1976, Variations in the Earth’s Orbit: pacemaker of the ice ages.” Science, 194, 1121- • P. Huybers, C. Wunsch, Nature 434, 491 (2005). • P. Huybers, 2006, Early Pleistocene Glacial Cycles • and the Integrated Summer Insolation Forcing. Science, 313,508-511

  28. End of Lecture 10

More Related