Transcript Institute of Hydrological Sciences

Chapter 5 of EARTH’S CLIMATE
Plate Tectonics and Climate
陳奕穎
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Plate tectonic process
Glaciation alternation
Climate model
Changes CO2
Greenhouse
BLAG Spreading Rate
Polar Position Hypothesis
Ex: 200Myr ago
Icehouse
Two hypotheses
Uplift Weathering
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Plate tectonics:
The scientific theory which describe Earth is called plate tectonics.
 Wegener[1914] 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
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
chemical composition
Continental crust (30-70 km)
Granites (花崗岩) 2.7 g/cm3
Ocean crust (5-10 km)
Basalts (玄武岩) 3.2 g/cm3
Mantle (Fe, Mg) to 2890 km
>3.6 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 Earth’s geography
 Energy from the magnetic field which result from molten
fluids circulating in Earth’s 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 world’s 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.
Laurasia
Gondwana
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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:
1. Distribution of land and sea
2. Global sea level
3. Topography
Using simplified
symmetrical
1000 m
Comparable to
today’s
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 Sun’s
energy weaker 1% than today’s.
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Output from the Model Simulation of
Pangaean Climate
 Dry continental
Downward
Uplift
climate
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
 BLAG[1983] (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
Change
CO2
Climate 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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Earth’s Negative Feedback
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Tectonic-scale Carbon cycle
Chemical weathreing on land
CaSiO3  CO2  CaCO3  SiO2
Silicate rock Atmosphere
Plankton
Plankton
Meltimg and transforma tion in subduction zone
CaSiO3  SiO2  SiCO3  CO2
Ocean sediment
Silicate rock
Atmosphere
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
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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.
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