Download Climate Science Lecture 7 – Chemical Weathering and Carbon

Climate Science
Lecture 7 – Chemical Weathering and Carbon
1) Carbon Reserviors on Earth
a) Vast majority in Sediments and Rocks
i) Limestone CaCO3
ii) Hydrocarbons – fossil fuels
b) A bit in the Deep Ocean
c) Tiny amounts in vegetation, ocean surface
water, soil, and atmosphere
ii) Dissolution – rain + atmospheric CO2
makes acid – acid weathers carbonate
rocks (common rocks at earth’s surface) –
creates ions that are used to build shells
and CO2 which returns to the atmosphere
(1) Dissolution generally returns the CO2
to the atmosphere, so it doesn’t help
store much
iii) So we rely on hydrolysis – the weathering
of silicate rocks to pull CO2 out of the
atmosphere and store it in sediments and
then rocks
2) Movement of Carbon between reservoirs
a) Rate inversely related to size of reservoir
i) e.g. vegetation to atmosphere has
continuously, second after second
ii) but, deep ocean to atmosphere is very
slow – centuries
4) Weathering depends on
iii) and, rocks to atmosphere takes millions of
a) Temperature – Bunsen burner in chem. lab
years
b) Precipitation – the water to make the acid
(1) Until recently (burning fossil fuels)
c) Vegetations – transfer CO2 to soil to make
b) Volcanic activity as a transfer mechanism
the acid
from earth’s interior (rocks) to atmosphere
i) Also, physical break rocks into smaller
i) Eruptions suddenly inject a large amount
bits – allows faster chemical weathering
of CO2 into the atmosphere
ii) Happens at such a rate that it does keep a 5) Weathering thermostat - negative feedback
certain flow of carbon from interior of
system
earth to the atmosphere
a) More CO2 in atmosphere (volcano or other
iii) Could this mechanism be the thermostat
source)
we are looking for – NO
b) Causes increase temp
iv) Thermostat must be effected by the
c) Causes increase precip
change they cause
d) Causes increase vegetation
(1) Explain spring of home thermostat
e) All 3 cause more weathering
v) Volcanic activity is unaffected by the
f) Weathering removes CO2 from atmosphere
concentration of CO2 in the atmosphere,
i) Over millions of years (response time)
therefore cannot be the thermostat
g) Less CO2 in atmosphere
vi) But volcanoes have been adding CO2 to
h) Causes decrease temp – decrease precip –
the atmosphere forever, why hasn’t it
decrease vegetation - negative feedback
built up and caused problems?
i) If CO2 decreases in atmosphere – temp dec –
(1) Especially considering the Young Sun
precip dec – vegetation dec – weathering dec
Paradox
– less CO2 removed from atmosphere –
vii) Answer – something must be removing
atmosphere warms, etc.
CO2 from the atmosphere at a rate
comparable to volcanic activities input
3) Chemical Weather as a removal mechanism
a) Two chemical reactions do this
i) Hydrolysis – rain + atmospheric CO2
makes acid – acid weathers silicate rocks
(most common rocks in earth’s crust,
especially in young mountains) – creates
ions that are used to build shells – which
end up as sediment then rock