Transcript Mechanism of sea level change - Atmospheric and Oceanic Sciences

Lecture 6
The Greenhouse Earth
Last 100 Myr
(Chapter 5)
Atmospheric CO2 Evolution
Last 100 Myr
100 myr ago:
mid-Cretaceous
Break up of Pangaea
Sea level 100-m higher
No ice sheet, even at the S.P.
Coral reefs extending 10o poleward to 40o
Why?
Warm Arctic
Cretaceous Climate and Modeling
Tropical thermostat and latitudinal surface temperature gradient (?)
Largest warming
in the Antarctic
due to the
absence of ice
sheet (with a
height of 3-4km)
Reading material:
Huber M., 2008, Science,
Vol. 321, 353-354
Model-data mismatch ?
Data problem: underestimation of tropical warming
1) Organism adaptation (but, why so many uncorelated organism?)
2) Missing interior land data
3) Tropical shell dissolved or recrystallized (appearing colder…)
Model problem: not good model yet (but what ‘s missing?)
The ocean heat transport hypothesis
Increased ocean heat transport==>reduced pole-equator temperature gradient
But
does the atmospheric heat transport compensates the ocean heat transport?
(Bjerkness hypothesis!)
coupled ocean-atmosphere model does not show reduced temperature gradient either!
Mid-Cretaceous salinity
Implication to CO2 and climate change
mid-Cratecous
Glacial maximum
1. No ice  less albedo feedback
(but, water vapor feedback positive!
Which is stronger?)
2. Radiative forcing = ln(CO2)
Two more issues:
Global sea level change
Asteroid Impact of 65Ma event
Global Sea Level Change
How to identify Global Sea Level Change
Evidence of Sea Level Change
Marine limestone
deposits form the
coasts of southern
England and northern
France
100 myr ago:
mid-Cretaceous
Evidences worldwide indicate sea level change in
global scale or the eustatic sea level
Mechanism of sea level change: I. change of volume of ridge
(high spreading rate wider ridge)
Mechanism of sea level change: II. Collision of continents
Collision “squeezes” the crust , increases the ocean area, reduces sea level
A check on spreading and colliding mechanism for sea level
Colliding
Low sea level
Fast
spreading/No
colliding
=>
high sea level
fast
Contribution to Sea Level Decrease (100 Ma to 0 Ma)
Cause of sea level change
Estimated change (m)
Geological factors
Decrease in ocean ridge volume
-50 to -150
Collision of India and Asia
-10
Climate factors (related to CO2)
Water stored in ice sheets
-50
Thermal expansion of sea water
-10
Total
-120 to -220
Last glacial maximum: 120 m lower sea level
Thermal expansion coefficient: 1/7000 /K
deep ocean 10K warming  10/7000 *5km ~ 7m
What about future global warming?
Contribution to Sea Level Change (uncertainty, version I)
Geological
factors
climate
factors
(related
to CO2)
65 Ma event
Distinction of 70% of species, including all dinosaurs
Why?
Evidence of Meteor Impact
Iridium:
rare on earth, but 10000 times more
abundant in some kinds of meteorites
Largest body every 50 – 100 myr
Site of Meteor Impact: Yucatan Peninsula, Mexico
Climatic impact of Meteor
200 km diameter
20km/s speed
11 Richter scale earth quake
100-1000 times stronger than
biggest earthquake
The 55 Ma abrupt warming event
~100,000 years long
Evidence in d18O and d13C
Possibly increased CO2 and CH4
But
NOT Asteriod impact (too long…)
Then:
What is the triggers for the increase of
GHGs?
References for Reading
Huber M., 2008, Science, Vol. 321, 353-354 (including
SOM)
End of Lecture 6
Mechanism of sea level change: III. Expansion of volcanic plateau