Class 10, Stable isotopes

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Class 10, Stable isotopes

  1. 1. GEOG5426 Stable isotopes
  2. 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. 3. S TA B L E I S OTO P E S I N PA L E O C L I M ATO LO GY
  4. 4. Isotopes are elements with the same number of protons but varying numbers of neutrons.
  5. 5. Stable isotopes are either not radioactive or decay so slowly that their half-lives cannot be measured.
  6. 6. Stable isotopes have the same chemical properties but don’t have the same atomic mass.
  7. 7. O16 O18
  8. 8. Stable isotopes of oxygen O16 99.76% O18 0.2% O17 0.04%
  9. 9. Photograph: David Sifry SMOW standard mean ocean water
  10. 10. Evaporation Condensation
  11. 11. Fractionation
  12. 12. H2O18 H2O18 H2O18 H H H2O16 H2O16 H2O16 H2O16 H2O16
  13. 13. H2O18 H2O18 H2O18 H H H2O16 H2O16 H2O16 H2O16 H2O16 H2O16 H2O16 H2O16
  14. 14. more O18 “enriched”
  15. 15. more O18 “enriched”
  16. 16. less O18 “depleted” more O18 “enriched”
  17. 17. more O18 “enriched”
  18. 18. more O18 “enriched” less O18 “depleted”
  19. 19. “heavy”
  20. 20. “heavy” “light”
  21. 21. O18 O16
  22. 22. O18 O16 small
  23. 23. O18 O16 small BIG
  24. 24. O18 O16 SMOW O18 O16 sample
  25. 25. “more positive” δO18 = “heavy” = “enriched” for example, ocean water
  26. 26. “more negative” δO18 = “light” = “depleted” for example, glacial ice
  27. 27. Source: Jouzel et al., Journal of Geophysical Research, 1994
  28. 28. Source: Jouzel et al., Journal of Geophysical Research, 1994 “light” “heavy”
  29. 29. paleothermometer
  30. 30. Source: Bowen and Revenaugh, Water Resources Research, 2003 δO18 in precipitation
  31. 31. Source: Bowen and Wilkinson, Geology, 2002 δO18 in precipitation
  32. 32. The “amount effect”: The greater the amount of rainfall, the lower the δO18 of the rainfall. (i.e., more negative)
  33. 33. O18 O18 O18 O18O16 O16 O16 O16O16
  34. 34. O18 O18 O18 O18O16 O16 O16 O16O16 O16 O16 “more negative” δO18 = “light” = “depleted”
  35. 35. O18 O18 O18 O18O16 O16 O16 O16 O16
  36. 36. O18 O18 O18 O18O16 O16 O16 O16 “more positive” δO18 = “heavy” = “enriched”
  37. 37. Source: Shanahan et al., Science, 2009 less O18 more negative “depleted” more O18 more positive “enriched”

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