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  • 1. GEOG5426 Stable isotopes
  • 2. November 24 Brief (15-minute) summaries of project topics. (1) What are the most important features of the modern climate in your region? (2) What proxies are available in your region, over the time interval specified? How are they related to climate? and (3) How different were past climates from modern conditions? Why is that important?
  • 3. S TA B L E I S O T O P E S I N PA L E O C L I M AT O L O GY
  • 4. Isotopes are elements with the same number of protons but varying numbers of neutrons.
  • 5. Stable isotopes are either not radioactive or decay so slowly that their half-lives cannot be measured.
  • 6. Stable isotopes have the same chemical properties but don’t have the same atomic mass.
  • 7. O 16 O 18
  • 8. Stable isotopes of oxygen O 18 0.2% O 17 0.04% O 16 99.76%
  • 9. SMOW standard mean ocean water Photograph: David Sifry
  • 10. Evaporation Condensation
  • 11. Fractionation
  • 12. H2O 16 H2O 16 H2O 16 H2O 18 H2O 18 H2O 18 H H2O 16 H2O 16 H
  • 13. H2O 16 H2O 16 H2O 16 H2O 16 H2O 16 H2O 16 H2O 18 H2O 18 H2O 18 H H2O 16 H2O 16 H
  • 14. “enriched” more O 18
  • 15. “enriched” more O 18
  • 16. “depleted” less O 18 “enriched” more O 18
  • 17. more O18 “enriched”
  • 18. “depleted” less O 18 more O18 “enriched”
  • 19. “heavy”
  • 20. “light” “heavy”
  • 21. O 18 O 16
  • 22. small O 18 O 16
  • 23. small O 18 O 16 BIG
  • 24. O 18 sample O 16 O 18 SMOW O 16
  • 25. “more positive” δO 18 = “heavy” = “enriched” for example, ocean water
  • 26. “more negative” δO18 = “light” = “depleted” for example, glacial ice
  • 27. Source: Jouzel et al., Journal of Geophysical Research, 1994
  • 28. “heavy” “light” Source: Jouzel et al., Journal of Geophysical Research, 1994
  • 29. paleothermometer
  • 30. Source: Bowen and Revenaugh, Water Resources Research, 2003 δO18 in precipitation
  • 31. δO18 in precipitation Source: Bowen and Wilkinson, Geology, 2002
  • 32. The “amount effect”: The greater the amount of rainfall, the lower the δO 18 of the rainfall. (i.e., more negative)
  • 33. O 18 O16 O18 O16 O18 O16 O18 O 16 O 16
  • 34. O 16 O 16 O 18 O16 O18 O16 O18 O16 O18 O 16 O 16 “more negative” δO18 = “light” = “depleted”
  • 35. O 16 O 16 O 18 O16 O18 O16 O18 O18 O 16
  • 36. O 16 O 16 O 18 O 16 O 18 O 18 O18 O 16 “more positive” δO 18 = “heavy” = “enriched”
  • 37. less O18 more negative “depleted” more O18 more positive “enriched” Source: Shanahan et al., Science, 2009