Plate Tectonics and Climate

1. Chapter 5 of EARTH’S CLIMATE Plate Tectonics and Climate 陳奕穎 Institute of Hydrological Sciences

2. Plate tectonic process Glaciation alternation Polar Position Hypothesis Climate model Changes CO2 Ex: 200Myr ago Greenhouse Icehouse Two hypotheses BLAG Spreading Rate Uplift Weathering

3. 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.

4. Structure and Composition of Tectonic Plates Earth Outer Layers 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

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

6. Plate boundaries • Divergent margins • Convergent margins • Transform fault margins

7. 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.

8. Magnetic lineations • Molten fluid record magnetic field.

9. 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.

10. 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.

11. 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.

12. Moving continents

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

14. Gondwana and South Pole

15. Glaciations and Continental Positions since 500 Myr Ago Why ? CO2 Icehouse Greenhouse

16. 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 ?

17. 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

18. 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.

19. 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

20. 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

21. 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 CO2 Climate change Change

22. Age of the seafloor • Spreading rates are as much as ten times faster in the Pacific than in Atlantic.

23. Earth’s Negative Feedback

24. Silicate rock Atmosphere Plankton Plankton Ocean sediment Silicate rock Atmosphere Tectonic-scale Carbon cycle Imbalance CO2 Climate changes

25. 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.

26. The Uplift Weathering Hypothesis • Chemical weathering • Rock exposure • Fresh rock • Exposure time Cooling down!

27. Fragmentation of Rock Weathering and Exposure Time

28. Three Hypotheses:

29. 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.