Lecture 24. Forces Stabilizing Climate_ Carbonate-Silicate Cycle by yurtgc548

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									Lecture 24. Forces Stabilizing Climate,
      Carbonate-Silicate Cycle.




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           reading: Chapter 4
                   Forces Stabilizing Climate


1. Presence of an atmosphere
      What happens on the Moon?
      How does an atmosphere stabilize climate during day and night?

        What happens when you have a ticker atmosphere?
        What happens when you have a thinner atmosphere?
           Seasons are Caused by Tilt (also called Obliquity)




                                     ecliptic = plane of the
                                         solar system




More solar radiation in the summer
Less solar radiation in the winter

Earth’s tilt angle: 23.5˚
            Forces Stabilizing Climate, cont.


2. Having a large Moon

 Moon very large compared to the Earth and other Moons.
 The Moon stabilizes the tilt of the Earth.
 This stabilizes the seasons.




            animation
                Forces Stabilizing Climate, cont.

Mars:
Currently Mars’ tilt is 25˚
No large Moons (2 tiny Moons: Deimos and Phobos)
Tilt is highly variable - chaotic.
Tilt varies between 0-60˚ on timescales of tens of
          thousands of years/millions of years




                                   ecliptic = plane of the
                                       solar system
        Mars at High and Low Tilt Angles


                                                       high tilt angle




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                                             low tilt angle
          Forces Stabilizing Climate, cont.

3. The Carbonate-Silicate Cycle

Unique feature of the Earth -
is a result of:

a. plate tectonics
b. volcanism         } having a geologically active planet
c. having oceans


Where does most CO2 come from?
Plate Tectonics
                Forming Carbonate Rocks

CO2 + H2O ---> H2CO3         (carbonic acid, dissolved in rainwater
                                and in the oceans)

Ca2+ + H2CO3 ---> CaCO3 + 2H+             (limestone + acid)


Where is most of the CO 2 in the Earth?
1x                tiny bit in atmosphere (270 ppm)
50x               dissolved in the oceans
30,000x           deposited as carbonate rocks (sedimentary rock)
1.7 millionx      dissolved in the mantle

If we were to put all carbonate rocks into the atmosphere, would
have an atmosphere similar to Venus.
                        Silicate/Rock Weathering


CaSiO3 + 2H2CO3 ---> Ca2+ + 2HCO3- + SiO2 + H2O

silicate    carbonic         ions                 quartz
 rock        acid

Another type of silicate rock:

2KAlSi3O8 + 2H2CO3 + 9H2O ---> 2K+ + 2HCO3- + 4H4SiO4 + Al2Si2O5(OH)4
feldspar   carbonic            ions           quartz    clay
            acid

Acid weathering of rocks produces ions (Ca2+, K+, Fe2+, Mg2+, etc.).
Ions washed into rivers and the oceans (ocean salinity).
Clays and quartz are produced.
Ions combine with H2CO3 to produce limestone.
                 Forming Carbonate Rocks

CO2 + H2O ---> H2CO3           (carbonic acid, dissolved in rainwater
                                  and in the oceans)

Ca2+ + H2CO3 ---> CaCO3 + 2H+               (limestone + acid)


Today:
Much of the limestone is biogenic (coral reefs, shells)
Some of the limestone is abiogenic.
                 Subduction



CaCO3 +       SiO2    --->   CaSiO3 + CO2

limestone    quartz          silicate
                              rock

metamorphic reaction: occurs at high T and P
               The Carbonate-Silicate Cycle



1.   CO2 outgassing from volcanos (greenhouse gas)
2.   CO2 dissolves in rain, lakes, streams, turns into carbonic acid
3.   Carbonic acid reacts with rocks, making ions, quartz, and clay
4.   Ions and dissolved CO2 reacts to make carbonate rocks
5.   Carbonate rocks are subducted
6.   Subducted carbonate rocks turned into CO2
            How Does this Cycle Stabilize Climate?

CO2 + H2O ---> H2CO3         (carbonic acid, dissolved in rainwater
                                and in the oceans)

Ca2+ + H2CO3 ---> CaCO3 + 2H+             (limestone + acid)

At high temperatures, more limestone is precipitated.
More CO2 dissolves in the oceans.
This cools climate and lower temperatures.
                                                    }   negative feedback
                                                        loop
CO2 Constantly Replaced By Subduction
            Earth’s Climate Is Obviously Not That Stable


1. The tilt undergoes precession (spinning like a top)
Alters how much solar radiation each hemisphere
        receives during summer and winter.
Cycles: 20,000 years

2. There are small variation in the Earth’s tilt
21.5 to 24.5˚
Cycles: 40,000 years

3. Small variation (5%) in Earth’s eccentricity
Changes the distance to the Sun, higher heating when closer.
Cycles: 100,000 years

Milankovitch cycles - could
trigger ice ages.
Lecture 25. Snowball Earth vs. Slushball Earth..




                       reading: Chapter 4

								
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