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Lecture 11: Glacial Cycles and Greehouse Gases
(Chapter 10)
Atmospheric CO2 Evolution
Uplift weatheringBLAG spreading rate,
Carbon balance at tectonic time scales
• Carbon sinks:
chemical weathering
subduction
• Carbon source:
volcanic eruption
Atmospheric CO2 Evolution
Uplift weatheringBLAG spreading rate,
Why in 100 yr cycle?
What is atmospheric CO2 during glacial cycles?
How do we know?
Ice core: A two-mile time machine
location at the dome to obtain the oldest ice
Ice core dating: annual layer countingice flow model
Ice coring project in
Greenland “summer”
Greenhouse gases tend to be globally uniform!
Trapping gases in ice core
CO2
CH4
Ice core records
Annual Cycle Jan Apr Jul Oct Jan
Charles David Keeling
CH4 and monsoon signal
CO2 change/Climate change:
100kyr cycle dominant
Question:
Chicken/egg ?
Vostok ice core
An even longer record
Comparison of CO2 and CH4
CO2 and climate: The last glacial cycle
Carbon Reservoir (0ka LGM)
Glacial carbon go to deep ocean
Carbon exchange
How to track carbon cycleduring glacial cycles?
Carbon isotope as marker
dards
dardssample
oooin CC
CCCCC
tan1213
tan12131213
/ )/(
)/()/(13
13C (99%), 12C(1%): stable isotope (nonradioactive) naturally occurring
14C (small residual): radioactive
Organic carbon: living plants (mostly in plants/photoplantons) ~ -22Inorganic 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.
Carbon reservoir, and their marker 13C values
Why organic δ13C more negative?
Photosynthesis and carbon isotope fractionation
Fractionation: Inorganic carbon (plant/plankton) form organic carbon
(tissue) with low 13C tissue, because plant/plankton favors 12C over 13C.
C3 and C4 pathways
Atmospheric inorganic carbon: δ13C ~ -7
C3 pathway: trees, shrubs, cool-climate grasses creates organic carbon: δ13C ~ -25C4 pathway: warm-climate grasses creates organic carbon: δ13C ~ -13
Dominant C3 (trees) so mean plant δ13C ~ -25
Vostok ice core
Glacial cycle of carbon
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
Quantify glacial carbon sink
= -530 GT
=-180 GT
The Deep Ocean, How?
Surf ocn CO2=Atms CO2 – 30ppm
= -300 GT
= -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)
C13 verification of missing carbon at glacial times are in deep ocean
Carbon and oxygen variation during glaciations
-0.4
Pacific sediment core
Glacial Bury Hypothesis?
(1) Ice sheet replace vegetation,(2) Colder/drier climate forest replaced by shrubs and grassesLess plants on continents ?But, can they be buried underneath ice sheet?(Ning et al. 2000,2010?)
Carbon Reservoir (0ka LGM)
Glacial carbon go to deep ocean
= -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)
C13 verification of missing carbon at glacial times are in deep ocean
A correction:?+ 530GT*(-25o/oo) + 180GT*(-7o/oo) =(38530GT)*(-0.27o/oo)
atmosphere
= -180 GT
Carbon and oxygen variation during glaciations
-0.4
Pacific sediment core
End of Lecture 11
Lecture 12: Carbon “Pumps” into the Deep Ocean
(Chapter 10)
How is carbon pumped into deep ocean?
Pump I: Solubility pump
warm,
low solubility
cold,
high solubility
EQ Pole
Glacial cooling about 2.5oC pumps atmospheric CO2 down by only about 10ppm (20ppm, half balanced by a 1psu salinity increase)
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.
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
Light + nutrients
Photosynthesis and Biological Pump
Primary Production and nutrients:
Annual carbon production in modern ocean: coastal, equator, southern ocean
Tropical pump, enough light, so nutrient (N, P) limited
Southern ocean pump, Not enough light, excess nutrients, but. iron limited.
Geoenginering: The Iron Hypothesis
Iron fertilization: enhancing biological pump
John Martin
How long the carbon can stay in the ocean?
Changes in Deep Ocean Circulation Modern circulation and 13C
Antarctic:incomplete photosynthesis less 12C to deep water lower 13C surface water
North Atlantic:complete photosynthesis more 12C to deep water high 13C surface water
aging:Downward more negative due to the downward rain of 12C-rich carbonMost clear where circulation is weak, e.g. N. Pacifci
Two end members
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
Change of North Atlantic circulation and Biological Pump
Reduced penetration of North Atlantic Deep WaterOr could it be a surface source change of 13C at LGM?
Obs: Δ 13C
Hol
ocen
eL
GM
Ideal AgeAMOCCCSM: Salinity
LGM: Older carbon, Younger deep water?
LGM modeling
Using deep tropical Atlantic 13C
Glacial:
stronger AABW,
weaker NADW
Interglacial: weaker AABW, stronger NADW
Evidence of changing deep circulation History of NADW/AABW
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
Change of North Atlantic circulation and Biological Pump
Implication to CO2 reduction
Reduced penetration of North Atlantic Deep Water
Enhanced Antactic overturning delievers more nutrient to the surfaceIncrease producitivytIncrese biological pumpReduce CO2(Circulation Pump)
How to measure the strengh of the soft tissue pump ?
Biological pump ~~ 13Csurf (+) - 13Cdeep (-) = 13C Vertical Difference >0
How to measure the strength of the biological pump
Nutrients and 13C vertical profile
Photosynthesis sends both 12C and nutrients (N,P) down
13Csurf (+)
13Cdeep(-)
less 12Cless nutrients
more 12Cmore nutrients
less nutrients
more nutrients
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
Surface foram: surface 13C
Benthic foram: Bottom 13C
More nutrients to surface
more Surface-Bottom >0
stronger biological pump
lower CO2
Past change of the Biological Pump
Stronger pump lower CO2
Pump III: (Bio)Chemical Pump (Carbonate pump, CaCO3 pump, Alkalinity pump)
Mineral calcium carbonate CaCO3 shells (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.
North Atlantic deep waterless corrosive
Antarctic bottom water, more corrosive
Change of North Atlantic circulation and (Bio)Chemical Pump
Implication to CO2 reduction
Reduced penetration of North Atlantic Deep Water
Enhanced Antactic Bottom waterIncrease corrosive and dissolution of CaCO3
More carbonate ion CO3
-2 to the surfaceDissolves surface CO2
Reduce surface CO2
(up to 40ppm)Polar Alkalinity hypothesis, Broecker and Peng,
Summary of Major Carbon Pumps
Soft tissue
Pump
(25 +?ppm)
Chemical pump (10+40ppm)
Solubility pump
(10 ppm)
Solubility pump
Biological pump
Chemical pump
Methane (CH4)
Source: Tropical wetland, monsoon rainfall controlBoreal wetland, summer warming control
Consistent with CH4/July Inso correlation23kyr signal dominates
Glacial-CO2 positive feedback
Colder climate
Lower CO2
Q2: Does it apply to anthropogenic global warming?
Q1: A key for great 100 kyr glacial cycle?
Glacial-CO2 positive feedback
CO2 decrease ==> Colder
Colder ==> CO2 decrease ?
Colder ==> solubility pump increases
==> soft tissue pump increases (stronger wind-upwelling,
more nutrient, iron…)
==> chemical pump increases
(circulation, PH level…)
==> more sea-ice ==> reduces CO2 release to the atmos.
==>stronger stratification==> reduce upwelling of deeper dissolved/reminirized carbon up)
Assessing Glacial-GHG feedbackPhase, lead/lag
23kyr
41kyr
21
63
23 kyr cycle, GHG leads ice volume, forcing41 kyr cycle, GHG in phase with ice volume, Feedback
Why different?
Reference for Reading
• Brovkin et al., 2007: Lowering of glacial atmospheric CO2 in response to changes in oceanic circulation and marine biogeochemistry. Paleoceanography, 22, PA4202, doi:10.1029/2006PA001380
End of Lecture 12
Pump III: Carbonate pump(CaCO3 pump)
32232 2 COHOHCOCO
The lack of H+, CaCO3 pump is effectively
Carbonate buffer