Lecture 7:
Back into the Icehouse:
Last 55 Myr
(Chapter 6)
CO2 evolution in the last 50 Myr
Did climate cool?
Cooling inferred from terrestrial evidences
Antarctic
Arctic
Northern mid-lattiude cooling inferred from leave shape
10-15oC
Problem with land records:
incomplete,
sporadic,
regional
Abyssal Time Machine (continuous!)
Cooling trend inferred from benthic foraminifera δ18O
Paleothermometer
Δδ18Oshell= Δδ18OW + Δδ18OT
i) Δδ18OT =ΔT/4.2oC
Cooler (temperature
dependence) increases
ii) Δδ18OW More continental ice
increases Δδ18OW (fractionation)
Evaporation水样
leads to fractionation
0 ‰ d18 O
+ ‰ d18 O
- ‰ d 18O
Heavy molecular more stable
standard
(SMOW)
heavy
light
Light isotope(16O)
Heavy (minor) isotope (18O)
Isotope fractionation
Fractonation Coefficients
‰ d18O
Equilibrium Fractionation
thermodynamic fractionation proportional to
temperature
-16
-14
-12
-10
-8
-6
-4
-2
1.016
1.014
1.012
1.01
1.008
1.006
1.004
1.002
-40
-20
0
20
40
60
Tem perature (C)
80
100
120
δ18O fractionation
d O
18
in o / oo
(18O /16O ) sample (18O /16O ) s tan dard
(18O /16O ) s tan dard
Antarctica and Greenland
all melting reduces
Δδ18OW from 0  -1
IAEA/WMO/GNIP Stations
(183 stations in 53 countries)
Long term mean seasonal cycle
Abyssal Time Machine (continuous!)
Cooling trend inferred from benthic foraminifera δ18O
13oC
Δδ18OT =1.75
Δδ18OW =1.0
Δδ18Oc =2.75
Δδ18OT =1.5,
Δδ18OW =0
Δδ18Oc =1.5
Paleothermometer
Δδ18Oshell= Δδ18OW + Δδ18OT
i) Δδ18OT =ΔT/4.2oC
Cooler (temperature
dependence) increases
ii) Δδ18OW More continental ice
increases Δδ18OW (fractionation)
An independent paleothermometer: Ma/Ca
Two independent paleothermometers
=> ice sheet
15oC
13oC
14oC
Abyssal Time Machine (continuous!)
Cooling trend inferred from benthic foraminifera d18O
Consistent evidence
Deep ocean/high
latitude cools by 15oC
over 55 myr
1) Cooler (temperature
dependence)
2) More continental ice
(fractionation)
Why does the climate cools?
Ocean Gateway Hypotheses
Hypothesis: Closing of Panama
isthmus (10-4 myr) redirects
warm/salty water northward,
preventing sea ice formation, more
evaporation to help glaciation
Hypothesis:Opening of Drake’s
Passage (20myr) cools the
Antarctic
Opening of Panama Isthmus
Hypothesis: Closing of Panama
isthmus (10-4 myr) redirects
warm/salty water northward,
preventing sea ice formation, more
evaporation to help glaciation
Problem: earlier by 2 myr for glacial
cycle
Modeling: opposite due to heat
transport
Drake Passage
Hypothesis:Opening of Drake’s
Passage (20myr) cools the
Antarctic
Problem: timing 10 myr before
intense glaciation, 10 myr after
first glaciation
Modeling: not too much effect,
Combined A+O heat transport not
much change
Lesson: needs to be more quantitative and comprehensive!
Ocean Gateway Hypotheses
Hypothesis: Closing of Panama
isthmus (10-4 myr) redirects
warm/salty water northward,
preventing sea ice formation, more
evaporation to help glaciation
Problem: earlier by 2 myr for glacial
cycle
Modeling: opposite due to heat
transport
Contradictory to each other!
Too much handwavering
Hypothesis:Opening of Drake’s
Passage (20myr) cools the
Antarctic
Problem: timing 10 myr before
intense glaciation, 10 myr after
first glaciation
Modeling: not too much effect
Why does the climate cools?
The Role of CO2
Reduced CO2:
•Slower input (BLAG)
•Faster removal (uplifting weathering)
•Increased coastal upwelling buried
enough organic carbon
Testing spreading (BLAG) hypothesis
No
??
OK
Testing uplifting weathering hypothesis
Tibetan Plateau
the unusually large uplifting in the last 20 myr
No major high topography like this in the last 150 myr
Tibetan Plateau
suspended particles, evidence of unusual physical weathering from Tibet
Himalayan sediments in the Indian Ocean:
Evidence of strong physical weathering
1) Steep terrain along the southern Himalaya
2) Uplift intensified monsoon (why?)
Positive feedback on uplifting
due to ice rock fragmentation
Feedbacks on uplifting weathering
Negative feedback on uplifting due
to chemical weathering
References for Reading
Tibet Uplift: Climate Impact
Asian monsoon
An, Z., Kutzbach, J. Prell, W. & Porter, S., 2001: Evolution of
Asian monsoons and phased uplift of the Himalaya-Tibetan
plateau since Late Miocene times. Nature, 411, 62-66
Boos and Kuang, 2010: Dominant control of the South Asian
monsoon by oragrphic insolation versus plateau heating. Science,
463, 218-222
Potential Impact on global thermohaline
Emile-Geay J., et al., 2003: Warren revisited: Atmospheric freshwater
fluxes and “Why is no deep water formed in the North Pacific”, Journal of
Geophysical Research, Vol.108(C6), 3178, doi:10.1029/2001JC001058
Early Pliocene Climate:
An Analogue for Future Global Warming Climate?
(move to later orbital…)
Fedorov A. et al., 2006: The Pliocene Paradox (Mechanisms for a
permanent El Nino). Science, 312, 1485-1489
Tropical Pacific SST changes (Wara et al. 2005)
d18O
West
SST
East
Strong gradient
∆SST
Weak gradient
End of Chapter 6
Volcanic aerosol cooling