1. Younger Dryas Period/ CO2-climate feedbacks
Chapter 14—Part 3
Younger Dryas Period/
CO2-climate feedbacks

2. CO2 Variations Bubbles in ice cores provide samples of ancient air.
These samples tell us that CO2 levels track the changes in temperature

3. CO2 T
CH4

4. Temperature and CO2 change together

5. CO2 Variations Bubbles in ice cores provide samples of ancient air.
These samples tell us that CO2 levels track the changes in temperature
This suggests CO2 can amplify climate change that is initiated by orbital variations.
How?

6. Weathering Volcanism The Weathering Cycle is TOO SLOW!
The weathering cycle operates over millions of years
Glacial climate changes take place over thousands of years
Weathering
CaSiO3 + CO2
CaCO3 + SiO2
Volcanism

7. The Biological Pump (marine organic carbon cycle)
transfer of CO2 to the deep ocean:
North Atlantic
Pacific Ocean
Transfer of carbon
Deep water

8. surface
water
Photosynthesis
CO2 + H2O  CH2O + O2
sinking particles
Respiration
CH2O + O2  CO2 + H2O
deep
water

9. Changes in the Biological Pump:
Atmospheric CO2 can decrease if more CO2 is stored
in deep waters

10. Changes in the Biological Pump:
Atmospheric CO2 can decrease if more CO2 is stored
in deep waters. This could be due to:
1) slower deep ocean circulation

11. Changes in the Biological Pump:
Atmospheric CO2 can decrease with more storage of CO2 in deep waters. This could be due to:
1) slower deep ocean circulation or
2) greater photosynthesis in surface waters

12. Changes in the Biological Pump:
Atmospheric CO2 can decrease with more storage of CO2 in deep waters. This could be due to:
1) slower deep ocean circulation or
2) greater photosynthesis in surface waters
More nutrients to the ocean?
Limiting nutrients: N, P, and Fe

13. Redfield Ratios These are the ratios of different elements in
living organisms
Element Relative # of atoms
C 106 N P Fe

14. Nitrogen in organisms
Amino acids (shown at left) are the building blocks of proteins
Nitrogen is part of the amino (NH2) group
Diagram from Wikipedia

15. Phosphorus in organisms
Phosphorus is a key component of nucleic acids, i.e., DNA and RNA
Nucleic acids also contain nitrogen

16. Iron in organisms Iron is used as part of various catalysts
There evidently is some iron in chlorophyll, but not much (main metal atom is Mg)
But, iron is required for the synthesis of chlorophyll

17. Possible glacial-interglacial CO2/climate feedback loops
Broecker’s “shelf hypothesis” (P)
Martin’s “iron hypothesis” (Fe)
“Coral reef hypothesis” (carbonate
saturation state)

18. Broecker’s “Shelf” hypothesis
Interglacial sea level
-Weathering
releases P
from rocks
-Some of this
P accumulates
in sediments
on the shelves
P-rich sediments
Glacial sea level
When sea level falls, P-rich sediments on the continental
shelves are washed into the deep ocean, raising productivity

19. The Shelf Hypothesis Feedback Loop
Start here
Atm. CO2
Surf. Temp. Ts
Continental
Ice Sheets
(+)
Sea
Level
Biological
Pump
P to
ocean
Shelf
exposure
 Positive feedback loop!

20. Martin’s “Iron hypothesis”
Iron is a limiting nutrient in parts of the ocean, especially the southern oceans near Antarctica
Iron is supplied to the oceans by windblown dust from the continents
Wind strength increases when the climate becomes glacial because the poles cool more than does the equator
Saharan dust plume

21. Iron Fertilization Feedback Loop
Start here
Atm. CO2
Surf. Temp. Ts
Equator to pole
Temp. gradient
(+)
Iron in Dust
to Ocean
Wind
Speeds
Biological
Pump
 Positive feedback loop!

22. Coral Reef Hypothesis Interglacial sea level Coral
(CaCO3)
CaCO3 + CO2 + H2O  Ca HCO3
Glacial sea level
Reefs form when sea level goes up  CO2 goes up
Reefs weather and dissolve when sea level goes down
 CO2 goes down

23. Coral reef feedback loop
Start here
Surf. temp Ts
Continental
glaciers
Sea
level
(+)
Atmospheric
CO2
Surface
ocean CO2
Reef
formation
 Positive feedback loop!

24. So, there are several positive feedback loops that may cause atmospheric CO2 to go up and down in concert with the glacial-interglacial cycles
Some combination of these feedback loops, combined with changes in ocean circulation, is probably responsible for the CO2 fluctuations seen in the Vostok ice core

25. Younger Dryas Period
Towards the end of the last Ice Age, climate warmed, then suddenly cooled again for almost 1000 yrs
The evidence comes from the reappearance of the Dryas flower in the Alps, which flourishes in glacial climates
Image from Wikkipedia

26. Younger Dryas Period Temperatures come from O and H isotopes
in ice cores
High 18O (or high
D/H)  warmer
temperatures
Younger Dryas

27. The Atlantic Conveyor
Did the oceanic thermohaline circulation shut down
during the Younger Dryas Period?

28. Atlantic Conveyor Shutdown
As the Laurentide ice sheet retreated, melt water was diverted from the Mississippi River to the St. Lawrence River
North Atlantic ocean became capped with freshwater  not dense enough to sink  thermohaline circulation shut down for ~1000 yrs
Could this happen again as a result of global warming?