Stable oxygen and carbon isotopes can be used as proxies for paleoclimate reconstruction. Oxygen isotopes in carbonate shells vary based on temperature and ice volume, providing information about glacial/interglacial cycles. Carbon isotopes reflect the global carbon cycle and can indicate changes in productivity, circulation, and terrestrial carbon storage over time.

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