Lecture 11: Cretaceous Hothouse and Sea Level Change

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Lecture 11 Cretaceous Hothouse and Sea Level
Change

• Climate hothouse at 100 Myr
• very important info about possible climate states
• geological context understood
• study role of CO2
• test GCMs
• Sea level changes
• controls
• implications

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Good Paleocontinental Reconstructions Available
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The Post-Pangaea World

• Sea-floor spreading, higher sea level lead to
  separate continents and emergent landmasses

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Climate-DataTargets for Models

• What differences or similarities do you see?
• Name three.

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Results from Basic GCM Simulations

• Hows the fit?
• Overall?
• In detail?

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Why the Mismatch? The Data?

• Fossils might be painting the wrong picture or
  may have been misinterpreted
• not likely
• Bias towards climate records from moderate
  coastal regions, as opposed to strongly seasonal
  interiors
• maybe
• Isotopic records have been degraded
• maybe

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Why the Mismatch? The Models?

• Models dont handle oceans well. They
• ignore upwelling
• are bad at deep ocean circulation
• miss small seas, lakes
• Was ocean circulation at 100 Myr fundamentally
  different?

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Different Cretaceous Ocean Circulation?
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Aside Non-Linearity of CO2 Forcing

• snow-ice positive feedback
• Saturation of CO2 greenhouse window

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Sea Level is Important
(now)
(100 Myr)
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Sea Level Has Varied
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Tectonic Controls on S.L., I
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Tectonic Controls on S.L., II
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Climate Controls on S.L.
Water storage in ice sheets Thermal
expansion of oceans
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Causes, Cretaceous Sea Level Changes
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Climate Impacts of Sea Level Change

• Change in surface extent of water vs. land
• Heat capacity of water
• moderates continental interiors
• Albedo of water versus rock and soil?
• ? What are the relative values?
• Productivity and carbon storage, marine versus
  terrestrial ecosystems?
• ? What might changes be if sea level rises?