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

Atmospheric CO 2 Evolution Uplift weathering BLAG spreading rate,

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

Atmospheric CO 2 Evolution Uplift weathering BLAG 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 counting ice flow model

Ice coring project in Greenland “summer”

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

CO 2 CH 4 Ice core records Annual Cycle Jan Apr Jul Oct Jan Charles David Keeling

CH 4 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 CO 2 and climate: The last glacial cycle

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

Carbon exchange

How to track carbon cycle during glacial cycles?

Carbon isotope as marker 13 C (99%), 12 C(1%): stable isotope (nonradioactive) naturally occurring 14 C (small residual): radioactive Organic carbon: living plants (mostly in plants/photoplantons) ~ -22 Inorganic carbon: HCO 3 -1, CO 3 -2 (water), CO 2 (air) ~ +1, Mostly in inorganic carbon (22 times more than organic carbon) such that the mean is ~ 0.

Carbon reservoir, and their marker  13 C values Why organic δ 13 C more negative?

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

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

Quantify glacial carbon sink = -530 GT =-180 GT  The Deep Ocean, How? Surf ocn CO 2 =Atms CO 2 – 30ppm = -300 GT

= -530 GT All glacial terrestrial carbon into the ocean lowers ocean  C 13 by o / oo 38000GT*0 o / oo + 530GT*(-25 o / oo )=(38530GT)*(-0.34 o / oo )  C 13 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 grasses  Less 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  C 13 by o / oo 38000GT*0 o / oo + 530GT*(-25 o / oo )=(8530GT)*(-0.34 o / oo )  C 13 verification of missing carbon at glacial times are in deep ocean A correction:? + 530GT*(-25 o / oo ) + 180GT*(-7 o / oo ) =(38530GT)*(-0.27 o / 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 EQPole Glacial cooling about 2.5 o C 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 CO 2 in these upper layer. Upon reminerization of this organic matter in the deeper layers, this CO 2 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  13 C Antarctic: incomplete photosynthesis  less 12 C to deep water  lower  13 C surface water North Atlantic: complete photosynthesis  more 12 C to deep water  high  13 C surface water aging: Downward more negative due to the downward rain of 12 C-rich carbon Most clear where circulation is weak, e.g. N. Pacifci Two end members

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

Obs: Δ 13 C Holocen e LGM Ideal Age AMOCCCSM: Salinity LGM: Older carbon, Younger deep water? LGM modeling

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

North Atlantic: complete photosynthesis  more 12 C to deep water  high  13 C surface water Antarctic: incomplete photosynthesis  less 12 C to deep water  lower  13 C 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 surface  Increase producitivyt  Increse biological pump  Reduce CO2  (Circulation Pump)

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

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

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

Surface foram: surface  13 C Benthic foram: Bottom  13 C 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, CaCO 3 pump, Alkalinity pump) Mineral calcium carbonate CaCO 3 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 CaCO 3 produces carbonate ion CO 3 -2, which when upwelled to the surface combines with dissolved CO 2 to produce bicarbonate ion HCO This process removes CO 2 from the surface waters, pumping carbon to the deep ocean.

North Atlantic deep water less 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 water  Increase corrosive and dissolution of CaCO 3  More carbonate ion CO to the surface  Dissolves surface CO 2  Reduce surface CO 2 ( 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 (CH 4 ) Source: Tropical wetland, monsoon rainfall control Boreal wetland, summer warming control Consistent with CH 4 /July Inso correlation 23kyr 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 feedback Phase, lead/lag 23kyr 41kyr kyr cycle, GHG leads ice volume, forcing 41 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: /2006PA001380

End of Lecture 12

Pump III: Carbonate pump (CaCO3 pump) The lack of H+, CaCO3 pump is effectively Carbonate buffer