Zachos et al 2001

• Warm deep ocean• Change in carbon also• First noted by Kennett

and Stott (1991)

Benthic foraminifera:• Change in δ13C of

deep ocean (also seenin surface ocean, landbiosphere)

• 5°C warming of deepocean

• Drop in δ13C takesplace quickly(<20kyr)

• Rise takes 100 kyr

Zachos et al. (2001)

What can cause 2.5 ‰ shift in δ13C ofocean/atm/biosphere carbon?

• Methane -60‰ (Dickens)40000GT(0‰) + 1700GT(-60‰) = 41700(-2.5‰)• Organic Carbon -25‰40000GT(0‰) + 4500GT(-25‰) = 44500GT(-2.5‰)• Mantle Carbon -5‰40000GT(0‰) + 40000GT(-25‰) = 800 00GT(-2.5‰) *This simple mass balance is an approximation. The added carbon will

impact ocean chemistry which will cause dissolution of calciumcarbonate from the seafloor. Also, as the ocean pH changes thisaffects the isotopic composition of carbonate slightly

CO2 + CO3= + H20 <-> 2HCO3

-

What happens when you put extracarbon into the ocean atmosphere system

quickly?• Take carbon and add it to the ocean• CO2 will increase, atmospheric pCO2 will

increase• But [CO3=] will decrease. This will cause

carbonates on seafloor to dissolve, whichwill bring CO2 back down

Zachos et al. (2005)

Zachos et al. (2005)

How do we know whether it isorganic carbon or methane?

• Carbon chemistry of the ocean suggests a large ( >4500GT) source (Zachos et al., 2005)

• Temperature change (5°C) requires a large source givenour best estimates of climate sensitivity (ΔT/ΔCO2)(Pagani et al., 2006)

• Reconciling climate sensitivity estimates, δ13C changesfrom terrestrial records, ocean chemistry requires hugeamounts of carbon.

Sources of organic carbon??• Contact metamormism of large igneous

province into organic rich sediments(evidence?)

• Global burning of peat (would have to startwith much more than we have today)

• The isolation of a large shallow seaway byplate tectonics, desication and respiration ofaerated organic matter

Higgins and Schrag (2006)

Transition to modernmammals

Gingerich 2006

Benthicforaminiferaextinction

Gingerich 2006

Dwarf mammal

Zachos et al 2001

Total Cenozoic range: 5.4‰

Antarctica 1.2‰Northern Hemisphere 1.1‰

Deep sea temperature 3.1‰

Cause of Cenozoic Glaciation

• External (sun, etc.) - unlikely• CO2 - indirect effect of plate tectonics• Plate tectonics: Position and height of

continents, position and depth of oceanpassages

Phanerozoic CO2 Reconstructions

Berner and Kothavala (2001)

Cenozoic CO2 reconstructions

Carbon isotope technique

δ13C of marine organic matter depends on:• δ13C of carbon in surface ocean• [CO2] in surface ocean

– T of surface ocean– pCO2 of atmosphere– Degree of equilibration between ocean and atmosphere

• Growth rate• Compound specific δ13C more reliable

From William White coursenotes

Boron isotope technique

• Boron speciation B(OH)4-, B(OH)3 depends

on pH• Boron in B(OH)4

- is 20‰ enriched in δ11B,so δ11B of B(OH)4 depends on speciation

• Foraminifera take up B(OH)4• Carbon speciation (HCO3

-, CO3=, CO2)

depends on pH

Pagani et al (2005)

Cause of Cenozoic Glaciation

• External (sun, etc.) - unlikely• CO2 - can explain increases in glaciation

before 25 million years ago, but not after• Plate tectonics: Position and height of

continents, position and depth of oceanpassages

Impact of Plate Tectonics onclimate

• Puts more land at high latitudes for glaciation• Elevation distribution (barrier to winds, high spot

= cold spot) can change atmospheric circulationpatterns. (Tibetan plateau)

• Ocean basins change shape, ocean currents changecourse. Ocean currents transport heat. (Gatewayhyotheses: Antarctic circumpolar, Panama)

Did development of ACC causeOligocene glaciation?

Antarctic Bottom Water

Decreased pCO2from 4xpresent to2xpresent over 10my

DeConto and Pollard (2003)

Elevation threshold

Crossing threshold canexplain inception ofOligocene ice sheet buthow about decay?

termination

Did Panama closure cause Plio-Pleistocene glaciation?

Atlantic Overturning Circulation

14 Sv

18 Sv

4 Sv

But how does bring warm water into highnorthern latitudes bring ice sheet growth?

Moisture? Moisture shuts down deep water formation? (Driscoll and Haug, 1998)

Lunt et alHadCM3

… but models say extra moisture not enough to build ice sheets… and data suggests Panama closed well before glaciation (4.6 mya)

Pacific ocean stratification?

Haug et al 2005: warmer summer temperatures and colder wintersin North Pacific

Impose stratification in low resolutionmodel…

But what causes stratification? Cooling? What causes cooling?

Pliocene/Pleistoceneintensification

• Panama closure• Pacific stratification• Uplift of Himalayas (CO2, Physical)