Lecture 6 The Greenhouse Earth Last 100 Myr (Chapter 5)

Last 100 Myr Atmospheric CO2 Evolution

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 10 o poleward to 40 o Why?

Warm Arctic

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, Cretaceous Climate and Modeling

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?)

Mid-Cretaceous salinity 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!

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(CO 2 )

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

fast A check on spreading and colliding mechanism for sea level Colliding  Low sea level Fast spreading/No colliding => high sea level

Contribution to Sea Level Decrease (100 Ma to 0 Ma) Cause of sea level changeEstimated 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?

Geologicalfactors climatefactors(relatedto CO2) Contribution to Sea Level Change (uncertainty, version I)

65 Ma event Distinction of 70% of species, including all dinosaurs Why?

Iridium: rare on earth, but times more abundant in some kinds of meteorites Largest body every 50 – 100 myr Evidence of Meteor Impact

Site of Meteor Impact: Yucatan Peninsula, Mexico Climatic impact of Meteor 200 km diameter 20km/s speed 11 Richter scale earth quake times stronger than biggest earthquake

~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? The 55 Ma abrupt warming event

Huber M., 2008, Science, Vol. 321, (including SOM) References for Reading

End of Lecture 6

Mechanism of sea level change: III. Expansion of volcanic plateau