![δ O18
• Oxygen isotopes
– 16O = 99.8% Analyze ratios on stable
isotope mass spectrometer
– 17O = 0.08%
– 18O = 0.2%
Measure the 2 most abundant isotopes
[18O/ 16Osample - 18O/ 16Ostandard]
δ O (‰) =
18
* 1000
18
O/ 16O standard
PeeDee Belemnite (PDB)
Standard = SMOW (Std Mean Ocean Water)](https://image.slidesharecdn.com/7stableisotopes-1-120416061825-phpapp01/85/7-stable-isotopes-1-3-320.jpg)
![Carbon Isotopes
• Stable Carbon isotopes
– 12C = 98.9% Analyze ratios on stable
isotope mass spectrometer
– 13C = 1.11%
– 14C = trace (radioactive)
Measure the 2 most abundant isotopes
[13C/ 12Csample – 13C/ 12Cstandard]
δ C=
13
* 1000
13
C/ 12C standard
PeeDee Belemnite (PDB)
Standard = SMOW (Std Mean Ocean Water)](https://image.slidesharecdn.com/7stableisotopes-1-120416061825-phpapp01/85/7-stable-isotopes-1-18-320.jpg)
7 stable isotopes-1
- 1. Stable Isotopes δ18O- oxygen isotopes temperature ice volume δ13C- carbon isotopes Carbon cycle
- 2. Oxygen Isotopes • Oxygen has 3 isotopes #protons #neutrons isotope 8 8 16 O 8 9 17 O 8 10 18 O
- 3. δ O18 • Oxygen isotopes – 16O = 99.8% Analyze ratios on stable isotope mass spectrometer – 17O = 0.08% – 18O = 0.2% Measure the 2 most abundant isotopes [18O/ 16Osample - 18O/ 16Ostandard] δ O (‰) = 18 * 1000 18 O/ 16O standard PeeDee Belemnite (PDB) Standard = SMOW (Std Mean Ocean Water)
- 4. Oxygen Isotopes δ18O • Calcite shells (foraminifera) = CaCO3 Seawater: HC16O16O16O HC18O16O16O HC17O16O16O CaC16O16O16O CaC16O16O18O Ratio in the foram CaCO3 reflects the ratio in the seawater
- 5. Oxygen Isotopes Ruddiman (App. 1)
- 6. Oxygen Isotopes • Differences in mass are great enough to make the atoms behave differently during physical and chemical processes • 1. Evaporation – 16O is lighter- evaporates more readily • 2. Incorporation into a solid – 16O greater vibrational energy- more difficult to incorporate into solid
- 7. Oxygen Isotopes • Evaporation Effect (Ice volume, salinity) – 16O preferentially evaporated – incorporated into rain and snow – Stored on land as ice – During glacials- more 16O removed from the ocean and stored on land – 18O/ 16O of remaining ocean becomes “heavier” (or higher δ18O) – Reservoir forams create shells from is enriched in 18O
- 8. Oxygen Isotopes • Temperature Effect – Differences in vibrational energies are more pronounced at lower temperatures – More discrimination against 16O when it is colder – Shells incorporate a greater % of 18O when it is cold (= heavier 18O/ 16O or δ18O)
- 9. δ O 18 • Rule of Thumb values • Ice volume effect: – ~1 ‰ δ18O/~100 m sea level • Temperature effect: – ~ 1 ‰ δ18O/~ 4°C – 0.25 ‰ /°C
- 10. Oxygen Isotopes • During glacials: – More water evaporated from ocean and stored on land as ice • 16O preferentially stored in ice • δ18O of seawater (and shells) is heavier – Water is colder • More discrimination against 16O • δ18O of shells is heavier
- 11. Interglacial 16 O 18 O Glacial * * * Remaining seawater higher δ18O Ice sheet lower δ18O Shells higher δ18O See KKC 14-3
- 12. Oxygen Isotopes • Two effects- work in the same direction • Ice Volume- more ice = – Increase δ18O of seawater (and shells) • Temperature effect- colder – Increase δ18O of shells – δ18Oforams • Higher during cool intervals and glacial • Lower during warm intervals and interglacials
- 13. Oxygen Isotopes • Advantages – Forams common in deep sea sediments • Large dataset- high resolution • Benthic forams = deep water • Planktonic forams = surface water – Can also measure on: • corals, molluscs, fish ootoliths, speleothems (carbonate) • lake sediments • Phosphates – animal teeth and bones • Ice cores
- 14. Oxygen Isotopes • Complications – Multiple effects (temperature, ice volume) – Salinity (local effect) Ruddiman (App. 1) - Vital effects- biological fractionation - Diagenetic alteration of carbonate - Rayleigh fractionation
- 15. Oxygen Isotopes • Calculating paleotemperature (assumptions) t (°C) = 16.9 – 4.2(δ18Oforams - δ18Oseawater) + 0.13(δ18Oforams - δ18Oseawater)2 Shackleton, 1974 Two unknowns: * temperature * δ18Oseawater for the past (ice volume)
- 16. Cenozoic Climate Change Record from benthic forams = bottom water temperatures Assume- mostly ice volume effect cooler more ice Zachos et al., 2000 Ice free temperatures
- 17. Pleistocene Climate IG More ice Cooler G *Last glacial max (LGM) * Trend toward cooler and more ice during glacial * Increasing amplitude of variations * 41k vs. 100k world (~600ky) Raymo, 1994 Site 607- North Atlantic
- 18. Carbon Isotopes • Stable Carbon isotopes – 12C = 98.9% Analyze ratios on stable isotope mass spectrometer – 13C = 1.11% – 14C = trace (radioactive) Measure the 2 most abundant isotopes [13C/ 12Csample – 13C/ 12Cstandard] δ C= 13 * 1000 13 C/ 12C standard PeeDee Belemnite (PDB) Standard = SMOW (Std Mean Ocean Water)
- 19. Carbon Isotopes • 12 C and 13C are fractionated during photosynthesis – Extent of fractionation depends on photosynthetic pathway • 12 C is preferentially incorporated into organic matter (smaller) – C3 trees/shrubs ~ -21 to -28 ‰ – C4 grasses ~ -11 to -15 ‰ – Marine organic matter ~ -22 ‰ • Reduced forms of carbon are strongly fractionated – CH4 ~ -50 to -60 ‰
- 20. Carbon Isotopes * Fractionation by pathway * Removal and burial of small percent of Major pathway 12 C enriched organic matter leaves seawater enriched Ruddiman App. 2
- 21. Carbon Isotopes • Processes that impact δ13C – Global carbon mass balance – Aging of water masses (circulation) – Air-sea exchange – Productivity
- 22. Carbon Isotopes •Global carbon mass balance • LGM vs. Holocene • Deep water δ13C was 0.32 to 0.46 ‰ lower during the LGM than today • Suggests transfer of ~ 500 gigatons of terrestrial organic matter to the ocean Global average δ13C of glacial (G) and Iinterglacial (I) deepwaters Boyle, 1992
- 23. Carbon Isotopes • Global carbon mass balance Carbon shift in terrestrial soils and mammal teeth Expansion of C4 plants (~8-4 Ma) Cerling et al., 1993 North Am Pakistan Paleosols - horse teeth enamel Mammal tooth enamel
- 24. Carbon Isotopes • Aging of water masses (circulation) • More decay = more release of 12C •Older water = lower δ13C δ13C of Σ CO2 (‰) Modern Pacific Ocean Modern Atlantic Ocean 0 1.0 0 0.4 0. 1.0 1 0. 2 5 0.4 0.7 0. 9 1 Depth (km) Depth (km) RF 2 -0.3 1.0 2 3 -0.2.1 -0 0.8 N ADW 3 PBW 0.0 PBW AB 0.7 0.6 W 4 4 0. 1 0.2 0.5 5 5 6 6 40N 20N 0 20S 40S 60S 40S 20S 0 20N 40N 60N 80N Latitude Latitude redrawn from Kroopnick, 1985
- 25. Carbon Isotopes • Aging of water masses (circulation) • Circulation during LGM Ruddiman, Ch. 10
- 26. Carbon Isotopes • Air-sea exchange •Paleocene-Eocene Thermal Maximum (PETM)- has been attributed to methane release •Impact on atmospheric and marine HCO3- δ13C Zachos et al., 2008
- 27. Carbon Isotopes •Productivity • Removal of 12C in surface waters (productivity) • Release of 13C in deep waters (decay) • Produces a surface to deep gradient. PACIFIC • Strangelove Ocean older younger Kroopnick, 1985
- 28. Carbon Isotopes • Productivity Organic • More 12C buried in matter organic-rich anoxic sediments • Leaves waters enriched in 13C so organic matter becomes heavier Ocean Anoxic Event 2- Late Cretaceous
- 29. Carbon Isotopes • Advantages – Less susceptible to diagenetic alteration – Easily measured along with δ18O – Global Carbon cycle- Productivity indicator – Chemostratigraphy • Complications – Multiple sources of variation – Vital effects