Plate%20Tectonics%20and%20Climate

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Plate Tectonics and Climate
Chapter 5 of EARTHS CLIMATE

• ???

Institute of Hydrological Sciences
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(No Transcript)
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Plate tectonics The
scientific theory which describe Earth is called
plate tectonics.

• Wegener1914 find the margins of eastern South
  America and western Africa, could fit together.

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Structure and Composition of Tectonic Plates

• Earth Outer Layers
• chemical composition
• Continental crust (30-70 km)
• Granites (???) 2.7 g/cm3
• Ocean crust (5-10 km)
• Basalts (???) 3.2 g/cm3
• Mantle (Fe, Mg) to 2890 km
• gt3.6 g/cm3
• Physical behavior
• Lithosphere (100 km)
• hard, rigid unit that forms the tectonic plates
• Asthenosphere (100-250 km)
• softer unit capable of flowing

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Tectonic plates

• The outer rigid layer of Earth is broken into
  about dozen major segments called plates.

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Plate boundaries

• Divergent margins
• Convergent margins
• Transform fault margins

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Evidence of past plate motions

• Earth magnetic field ? evidence of Plate
  tectonics rearranging Earths geography
• Energy from the magnetic field which result from
  molten fluids circulating in Earths liquid iron
  core.

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Magnetic lineations

• Molten fluid record magnetic field.

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Paleomagnetic determination of past location of
continents

• Basalt is the best rocks to use (rich in highly
  magnetic iron).
• No ocean crust older than 175 Myrs.
• For earlier interval, it must focus on basalts on
  the continent.
• 500Myrs less reliable because of increasing
  likelihood that their magnetic signatures have
  been rest to the magnetic field of a later time.

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Short Summery

• We can reconstruct the position of the continents
  with good accuracy back to 300 Myrs ago.
• To measure rates of the seafloor spreading in
  ocean basin.
• Even we can compile spreading rates over enough
  of the worlds ocean to estimate the global mean
  rate of creation and destruction of ocean crust.

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The Polar Position Hypothesis

• ice sheets should appear on continents when they
  located at polar or near-polar latitude,
• but no ice should appear anywhere on Earth if no
  continent exist anywhere near poles.

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Moving continents
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• Pengaea
• Laurasia North-central Asia, Europe, North
  American
• Gondwana Africa, Arabia, Antarctica, Australia,
  South America, and India.

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Gondwana and South Pole
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Glaciations and Continental Positions since 500
Myr Ago
Why ?
CO2
Icehouse
Greenhouse
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Modeling Climate on the Supercontinent Pangaea

• Climate scientist use general circulation models
  (GCMs) to evaluate the impact of geography as
  well as several other factors.
• Questions
• What level of atmospheric CO2 ?
• Dose it match geologic record ?

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Input to the Model Simulation of Pangaean Climate

• Boundary condiction

Distribution of land and sea
1.
Global sea level
2.
Topography
3.
Using simplified symmetrical
1000 m
Comparable to todays
200 Myr ago
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Input to the Model Simulation of Pangaean Climate
cont.

• 4.Climate modelers constrain the likely CO2 level
  in atmosphere.
• 5.Astrophysical modelers indicate Suns energy
  weaker 1 than todays.

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Output from the Model Simulation of Pangaean
Climate

• Dry continental climate

Downward
Uplift
1.the great expanses of land at subtropical
latitudes beneath the dry. 2.trade wind lose
most of their water vapor by the time they
reached the continental interior
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Output from the Model Simulation of Pangaean
Climate cont.

• Monsoon circulations

Different rates of response of the land and sea
to heating in summer and radiative heat loss in
winter
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Tectonic Control of CO2 Input

• BLAG1983 (the geochemists Robert Berner,
  Antonio Lasaga, Robert Garrels) Climate changes
  during the last several hundred million years
  have been driven mainly by changes in the rate of
  CO2 into the atmosphere by plate tectonic
  process.(spreading rate hypothesis)

Spreading rates
Climate change
CO2
Change
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Age of the seafloor

• Spreading rates are as much as ten times faster
  in the Pacific than in Atlantic.

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Earths Negative Feedback
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Tectonic-scale Carbon cycle
Imbalance CO2
Climate changes
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A Warmer Earth 100Myr Ago

• The global mean spreading rate was as much as 50
  faster 100Myr ago than it is at present, so the
  rate of input of CO2 from the rocks to atmosphere
  must be higher than today.

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The Uplift Weathering Hypothesis

• Chemical weathering
• Rock exposure
• Fresh rock
• Exposure time

Cooling down!
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Fragmentation of Rock
Weathering and Exposure Time
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Three Hypotheses
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Conclusions

• Plate tectonic process largely explains
  alternations between icehouse intervals.
• Atmospheric CO2 changes in tectonic-scale in the
  last hundred million years needed to explain the
  climate variability.
• Both spreading rate uplift hypotheses attempt
  to link the changes in CO2 and in plate tectonic.