•Warm deep ocean •Change in carbon also •First...
Transcript of •Warm deep ocean •Change in carbon also •First...
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
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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)