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Creating an Orbitally Tuned Chronology

Creating an Orbitally Tuned Chronology. Overview. A Brief History of Orbital Theory. Geomorphological evidence of past glaciations - orbital changes suspected. “This is the work of Ice!” 1837. Louis Agassiz - first proposed past ice age Joseph Adhemar - first to suggest precession control

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Creating an Orbitally Tuned Chronology

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  1. Creating an Orbitally Tuned Chronology

  2. Overview

  3. A Brief History of Orbital Theory Geomorphological evidence of past glaciations - orbital changes suspected “This is the work of Ice!” 1837 • Louis Agassiz- first proposed past ice age • Joseph Adhemar- first to suggest precession control • James Croll- linked reduced winter sunlight to increased snow accumulation Developed theory and predicted multiple glaciations

  4. A Brief History of Orbital Theory Milutin Milankovitch - First hypothesized that summer insolation at 65oN as most important control on ice sheets - Detailed calculations of insolation

  5. Orbital Cycles

  6. Eccentricity Only orbital cycle to change the total insolation Precession Effect of precession depends on ellipticity of orbit i.e. Eccentricity modulates precession Precession and Eccentricity Precession has greatest influence at low latitudes Anti-phased across hemispheres

  7. Obliquity Obliquity has greatest influence at high latitudes In phase across hemispheres

  8. Incoming Solar Radiation - Insolation Obliquity - Largest effect at high latitudes - In phase across hemispheres Precession - Largest effect at low latitudes - Anti-phased across hemispheres

  9. Orbital Signal in Climate Records Signal vs Noise • Signal • - original forcing recorded in proxy record • Noise • - distortion of signal • - additional signal not related to orbital forcing

  10. orbital forcing - climate responseUnderstanding of how climate worksTool for creating chronologies

  11. Ingredients for understanding orbital climate change • Proxy of climate change • Continuous record • Absolute age dating technique

  12. Emiliani 1955- Pleistocene temperatures Climate Proxy & Continuous Record

  13. Absolute Age Dating Techniques C14 dating in foraminiferaU234 - Th230 dating coral reefsAr40 - Ar39 dating palaeomagnetic reversals

  14. Hays, Imbrie & Shackleton, 1976 Continuous climate proxy recordsIndependent chronology

  15. Hays, Imbrie & Shackleton, 1976 Spectral analysis shows significant peaks at orbital frequencies

  16. Shackleton et al., 1990 Placed Brunhes-Matuyama magnetic reversal 5-7% older than accepted radiometric dates

  17. Assumptions Tuning target Tuning parameter Ingredients for creating an orbitally tuned chronology

  18. Orbital signal is present Time lag Nature of orbital forcing - climate response Continuous and complete record Assumptions

  19. Tuning Target

  20. Tuning Parameter Magnetic Susceptibility d18O Sapropels

  21. Simple Ice Sheet Model y = ice volume t = time b = nonlinearity coefficient Tm = time lag x = forcing

  22. Simple Ice Sheet Model y = ice volume t = time b = nonlinearity coefficient Tm = time lag x = forcing

  23. Lisiecki & Raymo 2005 - LR04 Stack Combined 57 d18O records to make “global” record

  24. Lisiecki & Raymo 2005 - LR04 Stack Distribution and number of records vary through time

  25. Lisiecki & Raymo 2005 - LR04 Stack

  26. Lisiecki & Raymo 2005 - LR04 Stack

  27. Alignment to the LR04 Stack

  28. Alignment to the LR04 Stack LR04 Site 1267

  29. The early Pliocene problem

  30. Conclusions • Characteristics of orbital cycles • Ingredients needed to understand orbital scale climate change • Importance of chronology & stratigraphy • How to use our understanding of orbital climate change to create age models

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