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