1. CO2 and Climate Change

2. The strongest period in climate cycles is about 100 thousand years
Lisiecki & Raymo, 2005
3.25
5.25
4.25
Shifts in insolation patterns appear to control shifts in global climate
The strongest period in climate cycles is about 100 thousand years
However, 100 ky is the weakest signal in the insolation forcing
Need amplifying feedbacks to explain

3. Planck’s Law: ‘blackbody’ radiation
A theoretical object that absorbs
all incoming electromagnetic radiation.
It emits radiation as a function of temperature
at thermodynamic equilibrium.

4. Blackbody temperature The sun radiates primarily in the visible.
Earth radiates in the IR.
Earth has a blackbody
Temperature below the
freezing point of water.
Sun (T~ 5780°K)
Earth (T~ 255°K)
Wavelength (microns)

5. Greenhouse effect
Atmosphere allows visible light to pass, but ‘greenhouse’ gases
(H20, CO2, CH4) trap outgoing infrared and warm the Earth.

11. Epica Dome C ice core (Antarctica)
CO2 (greenhouse gas) and D (temperature) vary repeatedly through multiple glacial cycles. The variations are approximately 90 ppmv.
CO2
(ppmv)
D (‰)
Temperature
Siegenthaler et al. (2005)

12. CO2 and D are nearly in phase.
Vostok ice core (Antarctica)
CO2 and D are nearly in phase.
Both lead 18O atm O2 (ice volume).
Both lead Greenland D and 18O ice
(Northern hemisphere temperature).
Time

13. These allow us to rule out several possible
Phase relationships (relative timing)
These allow us to rule out several possible
mechanisms for driving the CO2 changes.
Vostok ice core (Antarctica)
CO2 and D are nearly in phase.
Both lead 18O atm O2 (ice volume):
Ice volume change is not driving CO2 change
Both lead Greenland D and 18O ice
Northern hemisphere temperature not driving CO2 change

14. Carbon reservoirs
Most carbon is in solid earth.
Ocean has most of the rest (60:1)
Atmosphere small reservoir, but important!

15. Stable isotope fractionation may be diagnostic tool.
Isotopic fractionation
Stable isotope fractionation may be diagnostic tool.

16. Different carbon pools are isotopically distinct.
Carbon reservoirs
Different carbon pools are isotopically distinct.

17. Climate, ocean and land CO2
Climate changes themselves cannot account for the observed changes in CO2.
Changes in the terrestrial biosphere, evident in carbon isotopes in the ocean, are too small to explain CO2 change, and they indicate a shift in the wrong direction!

18. Biological pumps
to change atmospheric
CO2
Productivity near the
sea surface changes the chemistry of both the surface and deep ocean.

19. Coral reef hypothesis
Growth of coral reefs on flooded margins as sea level rises would have the effect of increasing atmospheric pCO2, but the timing is wrong.

20. Phosphate burial hypothesis
Burial of phosphate and other nutrients on shelves
as sea level falls, and then release during sea level rise would have the right effect on atmospheric pCO2, but again, the timing is wrong.

21. Productivity
Biological activity results
in systematic changes in
concentration and isotopic
ratio of bio-limiting and
bio-intermediate elements.

22. Carbon isotopes
Photosynthetic fractionation
of organic carbon leaves
seawater enriched in heavier
carbon-13. The resulting
Isotopic ratio in seawater is
then incorporated in CaCO3,
providing a nutrient-tracer.

23. Isotopic influences
Photosynthetic fractionation results in a strong negative correlation between nutrients and carbon isotopes. Gas exchange, local productivity, and global reservoir shifts can also influence 13C.
So 13C can be used as a tracer for water masses (circulation), although gradients are more reliable than the absolute values.

24. Evident in salinity and many other properties…
The meridional overturning circulation (MOC) produces North Atlantic Deep Water (NADW).
NADW
GEOSECS
Evident in salinity and many other properties…

25. Also evident in carbon isotopes (13C).
The meridional overturning circulation (MOC) produces North Atlantic Deep Water (NADW).
NADW
Kroopnick (1985)
Also evident in carbon isotopes (13C).

26. LGM meridional section, western basin
Paleocean circulation
The configuration was different, but not the rate of circulation?
Curry and Oppo (2005)

27. Cadmium as a tracer
Dissolved cadmium is
strongly correlated with
phosphate and nitrate.
Cd a “nutrient” tracer
High Cd = high nutrients

28. Cadmium as a tracer
Dissolved cadmium in bottom water is reflected in benthic foraminifera shells.

29. Ocean circulation
‘Biological pump’ and ‘conveyor belt’ combine to distribute nutrients and ‘nutrient proxies’ in ocean.

30. Combined proxies
Both carbon isotope and cadmium tracers support repeated glacial to interglacial changes in ocean circulation combine to distribute nutrients and ‘nutrient proxies’ in ocean.

31. Nutrient changes and pCO2.
Changes in the inventory or whole ocean distribution of nutrients could explain the observed shifts in pCO2.
But there is no evidence for change in whole ocean inventory, and no evidence for widespread oxygen depletion in the deep ocean. Signal is most evident in Atlantic, and is most likely circulation.

32. Nutrient shift
Carbon isotopes suggest a wholesale shift to lower values.
Cadmium harder to discern. If anything, there is a small change to lower values in glacial, opposite required shift.

33. Mean ocean isotopic ratio changed during ice age.
Ocean carbon shift
Mean ocean isotopic ratio changed during ice age.

34. Focus on Southern Ocean
It is the main region where deep ocean and in atmosphere are in nearly direct contact.

35. Southern Ocean
Nutrient utilization (dust?), stratification (sea ice?), and/or circulation combined with carbonate compensation
Remain the leading explanations for CO2 change.

37. Atmospheric CO2 I Greenhouse gases and the temperature of the Earth
II Ice core evidence that glacial pCO2 was 80 ppm lower.
III Could it be due to terrestrial biosphere change? No!
IV How did the ocean do it?
Physical - chemical property changes (T, S)
Physical pumps
Biological pumps (nutrients, Corg, alkalinity)