greenhouse earth: 100 ma geol 1130. paleoclimate research two components –observations i.e....
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Greenhouse Earth: 100 Ma
GEOL 1130
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Paleoclimate Research
• Two components– Observations
• i.e. fossils, sediments, chemical proxies
– Modeling • using observations to test climatic conditions, • see if observations are consistent with each other, • predict other climatic conditions that might be
recorded but not yet found.
• Observation – modeling comparisons extremely important to moving research forward
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100 Ma observations1. Broadleaf (breadfruit-type tree) fossils at
polar locationsa. Today found in tropical evergreen locations
2. Cold blooded animals to poles
3. Corals found between 40 N and Sa. Today found between 30 N and S
4. Sea level higher by at least 200 m
1 & 2 suggest that the atmosphere and ocean were much warmer
3 suggests that the oceans were much warmer
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Activity: Was heat distribution on Earth more or less efficient in the Cretaceous than it is today?
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Modeling Cretaceous Climate
• Activity: What are boundary conditions in this model that would be different from today?– Continental position– Sea level– Atmospheric CO2 concentration
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Modeling Results
• Ran model with changes in geography only and with changes in both geography and CO2– Which one does a
better job?
• Does either one get the right amount of latitudinal heat transport?
• What is a potential solution?
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Cretaceous ocean circulation?
• Today’s deep oceans filled with cold (~1-4 C), somewhat saline water
• Cretaceous deep ocean filled with warm (>10-15 C?) water?
• Warm water transported from the tropics to the poles would have dramatically increased the latitudinal heat transport
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Sea Level Change
• Two types of sea level change in geology– Relative – local tectonic or isostatic effects on
coast lines– Eustatic – global sea level changes
• In terms of climate change, eustatic sea level change is what we are interested in
• Terminology:– Transgression – rise in sea level– Regression – fall in sea level
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Sea Level Change
• Activity: If a continental shelf has a slope of 1:1000, how much far inland will the ocean travel if sea level rises by 1 meter?– 1000 m or 1 km!
• Is sea level today low or high? That is, is sea level at the continental break in slope or up on the shelf?
• How much would sea level rise if all the ice caps were to melt?
• How much land would we lose if sea level rose 70 m?
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Past Sea LevelNote today’s low sea level!!
Has sea level remained constant over time?
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Five potential causes for sea level change
1. Tectonic – mid ocean ridges– Activity: How does spreading rate affect the
volume of the ocean basins?– Thin vs fat mid ocean ridges:
• Ocean floor depth (m) = original depth + 350*age1/2
• Today’s ridge depth = 2500 m• Activity: What is the square root of 5, 10, 20, 40,
60, 80, 100? How much change in depth occurs over each period?
• Crust that is more than 60 Ma old has reached a relatively stable depth of 5500 m
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Plate spreading driver of sea level
• Faster spreading makes ocean basins more shallow, causing high sea level (ocean pushed up on to continents)
• Slower spreading…(visa versa)
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Drivers of sea level change
2. Tectonics – collisions– When continents collide, some of the
continental land mass is thickened (mountains and plateaus), shrinking continents and by default expanding oceans• Modern example?
– Tibetan Plateau started 55 Ma
3. Volcanic Plateaus– Take up room on ocean floor, displacing
water
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Drivers of sea level change
4. Climate:– Ice on land takes water out of the ocean– What is total range between greenhouse
world 100 Ma and 20,000 years ago?• ~300 m
5. Thermal expansion/contraction of sea water
– 1 part in 7000 for each degree C
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