1. Creating an Orbitally Tuned Chronology

2. Overview

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

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

5. Orbital Cycles

6. Precession and Eccentricity Eccentricity Only orbital cycle to change the total insolation Precession Effect of precession depends on ellipticity of orbit i.e. Eccentricity modulates precession 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 response Understanding of how climate works Tool for creating chronologies

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

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

13. C 14 dating in foraminifera U 234 - Th 230 dating coral reefs Ar 40 - Ar 39 dating palaeomagnetic reversals Absolute Age Dating Techniques

14. Hays, Imbrie & Shackleton, 1976 Continuous climate proxy records Independent 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. Ingredients for creating an orbitally tuned chronology Assumptions Tuning target Tuning parameter

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

19. Tuning Target

20. Tuning Parameter Sapropels  18 O Magnetic Susceptibility

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

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

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

27. Alignment to the LR04 Stack

28. LR04 Site 1267 Alignment to the LR04 Stack

29. The early Pliocene problem

30. 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 Conclusions