Chapter 14—Part 3

1. 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 http://www.pbs.org/wgbh/warming/stories/

4. Temperature and CO2 change together CO2 Temperature http://www.env.leeds.ac.uk/envi2150/lecture6/lecture6.html

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. 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 ElementRelative # of atoms C 106 N 15 P 1 Fe 0.01-0.1

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 http://www.isof.cnr.it/ppage/capob/synth.html

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 http://chaitanya1.wordpress.com/2007/07/09/strawberries/

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 Continental Ice Sheets Atm. CO2 Surf. Temp. Ts (+) Sea Level Shelf exposure P to ocean Biological Pump  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 Surf. Temp. Ts Equator to pole Temp. gradient Atm. CO2 (+) Wind Speeds Iron in Dust to Ocean Biological Pump  Positive feedback loop!

22. Coral reef (CaCO3) Coral Reef Hypothesis Interglacial sea level CaCO3 + CO2 + H2O  Ca++ + 2 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?