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Lecture 11: Glacial Cycles and Greehouse Gases

This lecture covers the evolution of atmospheric CO2 during glacial cycles, including the processes of uplift weathering, spreading rate, carbon sinks, and volcanic eruptions. It also explores how ice cores can provide valuable information about greenhouse gases in the past. The lecture concludes with a discussion on carbon pumps into the deep ocean and changes in deep ocean circulation.

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Lecture 11: Glacial Cycles and Greehouse Gases

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  1. Lecture 11: Glacial Cycles and Greehouse Gases (Chapter 10)

  2. Atmospheric CO2 Evolution Uplift weathering BLAG spreading rate,

  3. Carbon balance at tectonic time scales • Carbon sinks: chemical weathering subduction • Carbon source: volcanic eruption

  4. Atmospheric CO2 Evolution Why in 100 yr cycle? Uplift weathering BLAG spreading rate,

  5. What is atmospheric CO2 during glacial cycles?How do we know?

  6. Ice core: A two-mile time machine location at the dome to obtain the oldest ice Ice core dating: annual layer counting ice flow model

  7. Ice coring project in Greenland “summer”

  8. Trapping gases in ice core Greenhouse gases tend to be globally uniform!

  9. Annual Cycle Jan Apr Jul Oct Jan Ice core records CO2 Charles David Keeling CH4

  10. CH4 and monsoon signal

  11. An even longer record CO2 change/Climate change: 100kyr cycle dominant Question: Chicken/egg ? Vostok ice core

  12. CO2 and climate: The last glacial cycle Comparison of CO2 and CH4

  13. Carbon Reservoir (0ka  LGM) Glacial carbon go to deep ocean

  14. Carbon exchange

  15. How to track carbon cycleduring glacial cycles?

  16. Carbon isotope as marker 13C (99%), 12C(1%): stable isotope (nonradioactive) naturally occurring 14C (small residual): radioactive Organic carbon: living plants (mostly in plants/photoplantons) ~ -22 Inorganic carbon: HCO3-1, CO3-2 (water), CO2 (air) ~ +1, Mostly in inorganic carbon (22 times more than organic carbon) such that the mean is ~ 0.

  17. Carbon reservoir, and their marker 13C values Why organic δ13C more negative?

  18. Photosynthesis and carbon isotope fractionation Fractionation: Inorganic carbon (plant/plankton) form organic carbon (tissue) with low 13Ctissue, because plant/plankton favors 12C over 13C.

  19. C3 and C4 pathways Atmospheric inorganic carbon: δ13C ~ -7 C3 pathway: trees, shrubs, cool-climate grasses creates organic carbon: δ13C ~ -25 C4 pathway: warm-climate grasses creates organic carbon: δ13C ~ -13 Dominant C3 (trees) so mean plant δ13C ~ -25

  20. Glacial cycle of carbon Vostok ice core

  21. Glacial-Interglacial change of Carbon (Oxygen) Isotopes (a negative correlation) (1) Ice sheet replace vegetation, (2) Colder/drier climate forest replaced by shrubs and grasses  Less plants on continents More negative d13C

  22. Quantify glacial carbon sink The Deep Ocean, How? =-180 GT = -530 GT Surf ocn CO2=Atms CO2 – 30ppm = -300 GT

  23. C13 verification of missing carbon at glacial times are in deep ocean = -530 GT All glacial terrestrial carbon into the ocean lowers ocean C13 by -0.34o/oo 38000GT*0o/oo +530GT*(-25o/oo)=(38530GT)*(-0.34o/oo)

  24. Carbon and oxygen variation during glaciations Pacific sediment core -0.4

  25. Glacial Bury Hypothesis? • (1) Ice sheet replace vegetation, • (2) Colder/drier climate forest • replaced by shrubs and grasses • Less plants on continents ? But, can they be buried underneath ice sheet? (Ning et al. 2000,2010?)

  26. Carbon Reservoir (0ka  LGM) Glacial carbon go to deep ocean

  27. C13 verification of missing carbon at glacial times are in deep ocean = -180 GT = -530 GT All glacial terrestrial carbon into the ocean lowers ocean C13 by -0.34o/oo 38000GT*0o/oo +530GT*(-25o/oo)=(8530GT)*(-0.34o/oo) atmosphere A correction:? +530GT*(-25o/oo) +180GT*(-7o/oo) =(38530GT)*(-0.27o/oo)

  28. Carbon and oxygen variation during glaciations Pacific sediment core -0.4

  29. End of Lecture 11

  30. Lecture 12: Carbon “Pumps” into the Deep Ocean (Chapter 10)

  31. How is carbon pumped into deep ocean?

  32. EQ Pole cold, high solubility warm, low solubility Pump I: Solubility pump Glacial cooling about 2.5oC pumps atmospheric CO2 down by only about 10ppm (20ppm, half balanced by a 1psu salinity increase)

  33. Pump II: Biological Pump (soft tissue pump, carbon pump) Organic matter is produced in the uppermost sunlit layers of the ocean. A fraction of the organic tissue (soft tissue) sinks to the deeper ocean through settling particles or advection of dissolved organic carbon. This leads to a net consumtion of CO2 in these upper layer. Upon reminerization of this organic matter in the deeper layers, this CO2 is returned to the seawater. Thus, these biological processes lead to a net transfer of inorganic carbon from the surface into the abyss. This process is termed the “soft tissue” pump. Light + nutrients The key to soft tissue biological pump is nutrients (light is infinite): increased nutrient increases biological activity and in turn the downward pumping of carbon

  34. Photosynthesis and Biological Pump

  35. Tropical pump, enough light, so nutrient (N, P) limited Southern ocean pump, Primary Production and nutrients: Annual carbon production in modern ocean: coastal, equator, southern ocean Not enough light, excess nutrients, but. iron limited.

  36. Iron fertilization: enhancing biological pump Geoenginering: The Iron Hypothesis John Martin How long the carbon can stay in the ocean?

  37. Changes in Deep Ocean Circulation Modern circulation and 13C • North Atlantic: • complete photosynthesis • more 12C to deep water  high 13C surface water Two end members • Antarctic: • incomplete photosynthesis • less 12C to deep water  lower13C surface water aging: Downward more negative due to the downward rain of 12C-rich carbon Most clear where circulation is weak, e.g. N. Pacifci

  38. Change of North Atlantic circulation and Biological Pump • North Atlantic: • complete photosynthesis • more 12C to deep water  high 13C surface water • Antarctic: • incomplete photosynthesis • less 12C to deep water  lower13C surface water  Reduced penetration of North Atlantic Deep Water Or could it be a surface source change of 13C at LGM?

  39. LGM modeling LGM: Older carbon, Younger deep water? Obs: Δ13C CCSM: Salinity AMOC Ideal Age Holocene LGM

  40. Evidence of changing deep circulation History of NADW/AABW Glacial: stronger AABW, weaker NADW Interglacial: weaker AABW, stronger NADW Using deep tropical Atlantic 13C

  41. Change of North Atlantic circulation and Biological Pump Implication to CO2 reduction • North Atlantic: • complete photosynthesis • more 12C to deep water  high 13C surface water • Antarctic: • incomplete photosynthesis • less 12C to deep water  lower13C surface water • Enhanced Antactic overturning delievers more nutrient to the surface • Increase producitivyt • Increse biological pump • Reduce CO2 • (Circulation Pump)  Reduced penetration of North Atlantic Deep Water

  42. How to measure the strengh of the soft tissue pump ? Biological pump ~~ 13Csurf (+) - 13Cdeep (-) = 13C Vertical Difference >0

  43. How to measure the strength of the biological pump Nutrients and 13C vertical profile Photosynthesis sends both 12C and nutrients (N,P) down less nutrients less 12C less nutrients 13Csurf (+) 13Cdeep(-) more 12C more nutrients more nutrients

  44. How to measure the strengh of the soft tissue pump ? Biological pump ~~ 13C (surface) - 13C (deep) Vertical Difference of 13C: stronger photosynthesis  more organic 12C rain down  13C (surface) positive/13C (deep) negative  large vertical difference and stronger biological pump

  45. Past change of the Biological Pump • Surface foram: surface 13C • Benthic foram: Bottom 13C • More nutrients to surface •  more Surface-Bottom >0 • stronger biological pump • lower CO2 Stronger pump lower CO2

  46. Pump III: (Bio)Chemical Pump (Carbonate pump, CaCO3 pump, Alkalinity pump) Mineral calcium carbonate CaCO3shells (formed in the upper layers of the ocean mainly by 3 groups of organisms: Cocco-lithophorids (phytoplankton), foraminifers, and pteropods (zooplankton)) raindown to the depth as they die, eventually dissolve, either in the water column or in the sediments. Deep water dissolution calcium carbonate CaCO3 produces carbonate ion CO3-2 , which when upwelled to the surface combines with dissolved CO2 to produce bicarbonate ion HCO3-1. This process removes CO2 from the surface waters, pumping carbon to the deep ocean.

  47. Change of North Atlantic circulation and (Bio)Chemical Pump Implication to CO2 reduction North Atlantic deep water less corrosive Antarctic bottom water, more corrosive • Enhanced Antactic Bottom water • Increase corrosive and dissolution of CaCO3 • More carbonate ion CO3-2 to the surface • Dissolves surface CO2 • Reduce surface CO2 • (up to 40ppm)  Reduced penetration of North Atlantic Deep Water Polar Alkalinity hypothesis, Broecker and Peng,

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