Download The Carbon Cycle - San Jose State University

MET 112 Global Climate Change - Lecture 8
The Carbon Cycle
Eugene Cordero
San Jose State University
Outline




Earth system perspective
Carbon: what’s the big deal?
Carbon: exchanges
Long term carbon exchanges
1
MET 112 Global Climate Change
Goals
 We want to understand the difference
between short term and long term carbon
cycle
 We want to understand the main
components of the long term carbon cycle
2
MET 112 Global Climate Change
3
MET 112 Global Climate Change
An Earth System Perspective
 Earth composed of:
– Atmosphere
– Hydrosphere
– Cryosphere
– Land Surfaces
– Biosphere
 These ‘Machines’ run the Earth
 Holistic view of planet…
5
MET 112 Global Climate Change
The Earth’s history can be
characterized by different
geologic events or eras.
Hydrosphere
 Component comprising all liquid water
– Surface and subterranean (ground water)
 Fresh/Salt water
 Thus…lakes, streams, rivers, oceans…
 Oceans:
– Oceans currently cover ~ 70% of earth
– Average depth of oceans: 3.5 km
– Oceans store large amount of energy
– Oceans dissolve carbon dioxide (more later)
– Circulation driven by wind systems
– Sea Level has varied significantly over Earth’s history
– Slow to heat up and cool down
MET 112 Global Climate Change
8
Cryosphere
 Component comprising all ice
– Glaciers
– Ice sheets:
 Antarctica, Greenland, Patagonia
– Sea Ice
– Snow Fields
 Climate:
– Typically high albedo surface
– Positive feedback possibility Store large amounts of
water; sea level variations.
10
MET 112 Global Climate Change
Land Surfaces
 Continents
 Soils surfaces and vegetation
 Volcanoes
 Climate:
– Location of continents controls
ocean/atmosphere circulations
– Volcanoes return CO2 to atmosphere
– Volcanic aerosols affect climate
14
MET 112 Global Climate Change
Biosphere
 All living organisms; (Biota)
 Biota- "The living plants and animals of a
region.“ or "The sum total of all organisms alive
today”
– Marine
– Terrestrial
 Climate:
 Photosynthetic process store significant amount
of carbon (from CO2)
16
MET 112 Global Climate Change
Interactions Between Components of
Earth System
 Hydrologic Cycle (Hydrosphere, Surface,and
Atmosphere)
– Evaporation from surface puts water vapor into
atmosphere
– Precipitation transfers water from atmosphere to
surface
 Cryosphere-Hydrosphere
– When glaciers and ice sheets shrink, sea level rises
– When glaciers and ice sheets grow, sea level falls
18
MET 112 Global Climate Change
When ice sheets melt and thus sea
levels rise, which components of the
earth system are interacting?
H
ph
e
yd
io
s
re
-B
ro
s
ph
e
he
re
-B
io
s
ry
o
os
p
tm
e
re
0% 2%
s.
..
...
re
-C
A
yd
ro
s
ph
e
yd
ro
p
re
-H
he
H
os
p
tm
A
tm
os
p
he
re
-C
ry
os
p
...
5% 5%
ph
er
Atmosphere-Cryosphere
Atmosphere-Hydropshere
Hydrosphere-Cryosphere
Atmosphere-Biosphere
Hydrosphere-Biosphere
A
1.
2.
3.
4.
5.
89%
When water from lakes and the ocean
evaporates, which components of the
earth system are interacting?
Land Surface – atmosphere
Hydrosphere-atmosphere
Hydrosphere-land surface
Crysophere-Atmosphere
Biosphere-Atmosphere
88%
5%
0% 2%
...
-A
tm
os
ph
er
e
..
os
p
ph
er
e
At
m
io
s
B
C
ry
s
op
he
re
-
re
-la
nd
su
.
..
m
os
p.
ph
e
ro
s
yd
H
H
yd
ro
s
ph
e
–
re
-a
t
at
m
o.
..
5%
Su
rf
ac
e
nd
La
1.
2.
3.
4.
5.
The Earth’s history can be
characterized by different
geologic events or eras.
Interactions (cont)
 Components of the Earth System are linked by
various exchanges including
 Energy
 Water (previous example)
 Carbon
 In this lecture, we are going to focus on the
exchange of Carbon within the Earth System
23
MET 112 Global Climate Change
Carbon: what is it?
 Carbon (C), the fourth most abundant element
in the Universe,
 Building block of life.
– from fossil fuels and DNA
– Carbon cycles through the land (bioshpere),
ocean, atmosphere, and the Earth’s interior
 Carbon found
– in all living things,
– in the atmosphere,
– in the layers of limestone sediment on the
ocean floor,
– in fossil fuels like coal.
MET 112 Global Climate Change
25
Carbon: where is it?
 Exists:
– Atmosphere:
–CO2 and CH4 (to lesser extent)
– Living biota (plants/animals)
–Carbon
– Soils and Detritus
–Carbon
–Methane
– Oceans
–Dissolved CO2
–Most carbon in the deep ocean
MET 112 Global Climate Change
27
Carbon conservation
 Initial carbon present during Earth’s formation
 Carbon doesn’t increase or decrease
globally
 Carbon is exchanged between different
components of Earth System.
29
MET 112 Global Climate Change
The Carbon Cycle
 The complex series of reactions by which carbon
passes through the Earth's
– Atmosphere
–
–
 Carbon is exchanged in the earth system at all time
scales
- Short term cycle (from seconds to a few years)
30
MET 112 Global Climate Change
The Carbon Cycle
 The complex series of reactions by which carbon
passes through the Earth's
– Atmosphere
– Land (biosphere and Earth’s crust)
– Oceans
 Carbon is exchanged in the earth system at all time
scales
- Long term cycle (hundreds to millions of years)
- Short term cycle (from seconds to a few years)
31
MET 112 Global Climate Change
The carbon cycle has different
speeds
Short Term Carbon Cycle
Long Term Carbon Cycle
Short Term Carbon Cycle
 One example of the short term carbon cycle involves plants
 Photosynthesis: is the conversion of carbon dioxide and
water into a sugar called glucose (carbohydrate) using
sunlight energy. Oxygen is produced as a waste product.
 Plants require
 Sunlight, water and carbon, (from CO2 in atmosphere or
ocean) to produce carbohydrates (food) to grow.
 When plants decays, carbon is mostly returned to the
atmosphere (respiration)
 During spring: (more photosynthesis)
 atmospheric CO2 levels go down (slightly)
 During fall: (more respiration)
 atmospheric CO2 levels go up (slightly)
35
MET 112 Global Climate Change
36
MET 112 Global Climate Change
Carbon exchange (short term)
 Other examples of short term carbon
exchanges include:
 Soils and Detritus:
- organic matter decays and releases carbon
 Surface Oceans
– absorb CO2 via photosynthesis
– also release CO2
38
MET 112 Global Climate Change
Short Term Carbon Exchanges
In Class Question
Explain why CO2 concentrations
goes up and down each year
Long Term Carbon Cycle
Long Term Carbon Cycle

Carbon is slowly and continuously being transported
around our earth system.
– Between atmosphere/ocean/biosphere
– And the Earth’s crust (rocks like limestone)

The main components to the long term carbon cycle:
1. Chemical weathering (or called: “silicate to
carbonate conversion process”)
2. Volcanism/Subduction
3. Organic carbon burial
4. Oxidation of organic carbon
43
MET 112 Global Climate Change
Long Term Carbon Cycle

Carbon is slowly and continuously being transported
around our earth system.
– Between atmosphere/ocean/biosphere
– And the Earth’s crust (rocks like limestone)

The main components to the long term carbon cycle:
1. Chemical weathering (or called: “silicate to
carbonate conversion process”)
2. Volcanism/Subduction
3. Organic carbon burial
4. Oxidation of organic carbon
44
MET 112 Global Climate Change
The Long-Term Carbon Cycle
(Diagram)
Subduction/
Volcanism
Atmosphere (CO2)
Ocean (Dissolved CO2)
Biosphere (Organic Carbon)
Silicate-toCarbonate
Conversion
Carbonates
Organic
Carbon
Burial
Oxidation
of Buried
Organic
Carbon
Buried Organic Carbon
45
MET 112 Global Climate Change
Where is most of the carbon today?
 Most Carbon is ‘locked’ away in the earth’s crust (i.e.
rocks) as
– Carbonates (containing carbon)
 Limestone is mainly made of calcium carbonate
(CaCO3)
 Carbonates are formed by a complex geochemical
process called:
– Silicate-to-Carbonate Conversion (long term carbon
cycle)
47
MET 112 Global Climate Change
Silicate to carbonate conversion –
chemical weathering
One component of the long term
carbon cycle
Granite (A Silicate Rock)
49
MET 112 Global Climate Change
Limestone (A Carbonate Rock)
50
MET 112 Global Climate Change
Silicate-to-Carbonate Conversion
1. Chemical Weathering Phase
• CO2 + rainwater  carbonic acid
• Carbonic acid dissolves silicate rock
2. Transport Phase
• Solution products transported to ocean by
rivers
3. Formation Phase
• In oceans, calcium carbonate precipitates
out of solution and settles to the bottom
52
MET 112 Global Climate Change
Silicate-to-Carbonate Conversion
Rain
2. Acid
Dissolves
Silicates
(carbonic
acid)
Land
1. CO2 Dissolves in
Rainwater
3. Dissolved Material Transported
to Oceans
4. CaCO3 Forms in
Ocean and Settles to
the Bottom
Calcium carbonate
MET 112 Global Climate Change
54
Changes in chemical weathering
 The process is temperature dependant:
– rate of evaporation of water is temperature
dependant
– so, increasing temperature increases weathering
(more water vapor, more clouds, more rain)
 Thus as CO2 in the atmosphere rises, the planet
warms. Evaporation increases, thus the flow of carbon
into the rock cycle increases removing CO2 from the
atmosphere and lowering the planet’s temperature
– Negative feedback
56
MET 112 Global Climate Change
Earth vs. Venus
 The amount of carbon in carbonate minerals (e.g.,
limestone) is approximately
– the same as the amount of carbon in Venus’
atmosphere
 On Earth, most of the CO2 produced is
– now “locked up” in the carbonates
 On Venus, the silicate-to-carbonate conversion process
apparently never took place
58
MET 112 Global Climate Change
Subjuction/Volcanism
Another Component of the Long-Term
Carbon Cycle
Subduction
Definition: The
process of the
ocean plate
descending
beneath the
continental plate.
During this
processes, extreme
heat and pressure
convert carbonate
rocks eventually
into CO2
61
MET 112 Global Climate Change
Volcanic Eruption
Eruption injected
(Mt – megatons)
17 Mt SO2,
42 Mt CO2,
3 Mt Cl,
491 Mt H2O
Can inject large amounts of
CO2 into the atmosphere
Mt. Pinatubo (June 15, 1991)
63
MET 112 Global Climate Change
Organic Carbon Burial/Oxidation of
Buried Carbon
Another Component of the Long-Term
Carbon Cycle
Buried organic carbon (1)
 Living plants remove CO2 from the atmosphere
by the process of
– photosynthesis
 When dead plants decay, the CO2 is put back
into the atmosphere
– fairly quickly when the carbon in the plants is
oxidized
 However, some carbon escapes oxidation when
it is covered up by sediments
66
MET 112 Global Climate Change
Organic Carbon Burial Process
O2
CO2
Removed
by PhotoSynthesis
CO2 Put Into
Atmosphere by
Decay
C
C
Some Carbon
escapes
oxidation
C
Result: Carbon into land
68
MET 112 Global Climate Change
Oxidation of Buried Organic Carbon
 Eventually, buried organic carbon may be
exposed by erosion
 The carbon is then oxidized to CO2
69
MET 112 Global Climate Change
Oxidation of Buried Organic Carbon
Atmosphere
Buried Carbon
(e.g., coal)
70
MET 112 Global Climate Change
Oxidation of Buried Organic Carbon
Atmosphere
Erosion
Buried Carbon
(e.g., coal)
71
MET 112 Global Climate Change
Oxidation of Buried Organic Carbon
Atmosphere
CO2
O2
C
Buried Carbon
Result: Carbon into atmosphere (CO2)
72
MET 112 Global Climate Change
The (Almost) Complete Long-Term
Carbon Cycle
 Inorganic Component
– Silicate-to-Carbonate Conversion
– Subduction/Volcanism
 Organic Component
– Organic Carbon Burial
– Oxidation of Buried Organic Carbon
74
MET 112 Global Climate Change
The Long-Term Carbon Cycle
(Diagram)
Subduction/
Volcanism
Atmosphere (CO2)
Ocean (Dissolved CO2)
Biosphere (Organic Carbon)
Silicate-toCarbonate
Conversion
Carbonates
Organic
Carbon
Burial
Oxidation
of Buried
Organic
Carbon
Buried Organic Carbon
76
MET 112 Global Climate Change
77
MET 112 Global Climate Change
Review of Long Term Carbon Cycle
79
MET 112 Global Climate Change
If volcanism was to increase over a period of
thousands of years, how would this affect
atmospheric CO2 levels?
Atmospheric CO2 levels would
Increase
Decrease
Stay the same
Are not related to
volcanism
22%
e
4%
vo
l..
el
at
ed
to
th
e
re
no
tr
St
ay
A
.
sa
m
e
ea
s
ec
r
D
re
a
se
4%
In
c
1.
2.
3.
4.
69%
If the silicate to carbonate conversion process
was to increase over a period of millions of years,
how would this affect volcanism?
Volcanism would
30%
...
e
th
e
d
by
th
e
N
ot
b
e
af
fe
ct
e
St
ay
D
ec
r
ea
s
sa
m
e
se
13% 13%
re
a
Increase
Decrease
Stay the same
Not be affected by
the silicate to
carbonate
conversion process
In
c
1.
2.
3.
4.
43%
If the oxidation of organic carbon was to
increase, how would global temperatures
respond?
Global temperatures
Would increase
Would decrease
Would stay the same
Are not affected by
the oxidation of
organic carbon
A
th
.
by
ct
ed
ffe
re
no
ta
ld
W
ou
..
m
e
sa
th
e
st
ay
de
ld
W
ou
ld
in
cr
cr
ea
ea
s
se
e
7% 2% 2%
W
ou
1.
2.
3.
4.
89%
If there was a decline in the silicate to carbonate
conversion process, how would global
temperatures respond?
Global temperatures
Would increase
Would decrease
Would stay the same
Are not affected by
the silicate to
carbonate
conversion process
17%
13%
th
e
by
ct
ed
ffe
ta
ld
A
re
no
W
ou
MET 112 Global Climate Change
...
m
e
sa
th
e
st
ay
de
ld
W
ou
ld
in
cr
cr
ea
ea
s
se
e
4%
W
ou
1.
2.
3.
4.
65%
83
Activity (groups of two)
Imagine that the global temperature were to
increase significantly for some reason.
1. How would the silicate-to-carbonate
conversion process change during this
warming period. Explain.
2. How would this affect atmospheric CO2
levels and as a result, global temperature?
3. What type of feedback process would this
be and why (positive or negative)?
84
MET 112 Global Climate Change
The silicate to carbonate conversion
processes would
Increase
Decrease
Remain unchanged
Impossible to tell
ll
to
ge
e
si
bl
po
s
Im
un
ai
n
MET 112 Global Climate Change
0%
te
e
ea
s
ec
r
R
em
0 of 5
0%
d
0%
D
In
c
re
a
se
0%
ch
an
1.
2.
3.
4.
Imagine that the global temperature were
to increase significantly for some reason.
85
How would atmospheric CO2 levels change?
Increase
Decrease
Stay the same
Impossible to tell
ll
te
e
si
bl
po
s
Im
MET 112 Global Climate Change
0%
to
sa
m
e
ea
s
St
ay
0 of 5
0%
e
0%
ec
r
D
In
c
re
a
se
0%
th
e
1.
2.
3.
4.
86
How would this affect global temps?
Increase
Decrease
Stay the same
Impossible to tell
ll
te
e
si
bl
po
s
Im
MET 112 Global Climate Change
0%
to
sa
m
e
ea
s
St
ay
0 of 5
0%
e
0%
ec
r
D
In
c
re
a
se
0%
th
e
1.
2.
3.
4.
87
What type of feedback process would
this be
Positive
Negative
Neither
Both
N
MET 112 Global Climate Change
ot
h
er
0%
B
0%
ei
th
eg
a
tiv
tiv
e
Po
si
0 of 5
0%
e
0%
N
1.
2.
3.
4.
88
Effect of Imbalances
Imbalances in the long-term carbon cycle can cause
slow, but sizeable changes in atmospheric CO2
What would
happen?
Atmosphere-Ocean-Biosphere
Earth’s Crust
91
MET 112 Global Climate Change
 Consider the long term carbon cycle as seen below
 Suppose the Atmosphere-Ocean-Biosphere has 40,000 Gt* of
carbon and the earth’s crust has 40,000,000 Gt of carbon
Atmosphere-Ocean-Biosphere
*1 Gt = 1015 grams
Earth’s Crust
92
MET 112 Global Climate Change
 Suppose that an imbalance developed in which the amount
leaving the Atm/Ocean/Biosphere was to decrease by 1%.
 If the arrows represent flux (carbon moving), and flux from the
Earth’s crust to the atm/ocean/bio (labeled B) is 0.03Gt/year,
what would the flux be for arrow A?
Atmosphere-Ocean-Biosphere
40,000 Gt
*1 Gt = 1015 grams
A
B
0.0300
Gt./yr
Earth’s Crust
40,000,000 Gt
Arrow A would be
0.03 Gt/yr
0.3 Gt/yr
0.0297 Gt/yr
0.0303 Gt/yr
r
G
t/y
03
0.
03
97
0.
MET 112 Global Climate Change
0%
G
t/y
t/y
r
G
3
0.
G
t/y
03
0.
0 of 5
0%
r
0%
r
0%
02
1.
2.
3.
4.
94
 For such an imbalance as shown below, what is the net
carbon flux and in what direction?
Atmosphere-Ocean-Biosphere
40,000 Gt
0.0297
Gt./yr A
*1 Gt = 1015 grams
B
0.0300
Gt./yr
Earth’s Crust 40,000,000 Gt
95
MET 112 Global Climate Change
For such an imbalance as shown below, what is
the net carbon flux and in what direction?
0.033 - up
0.033 down
0.0003 up
0.0003 down
MET 112 Global Climate Change
0%
w
n
0.
00
03
do
03
w
n
do
0.
03
3
3
03
0.
0 of 5
0%
up
0%
-u
p
0%
0.
00
1.
2.
3.
4.
96
 Based on the below Carbon Flux information, how many
years will it take for the carbon in the atm/ocean/bio to
double?
*1 Gt = 1015 grams
Atmosphere-Ocean-Biosphere
40,000 Gt
Net Carbon Flux
0.0297
Gt./yr A
B
0.0300
Gt./yr
Earth’s Crust
40,000,000 Gt
0.0003 Gt./yr
How many years will it take for the carbon in the
atm/ocean/bio to double?
0.03 years
12 years
100,000 years
133 million years
ar
s
ye
io
n
0
m
ill
3
13
10
MET 112 Global Climate Change
0%
ye
ar
s
ye
12
ye
a
0.
03
0 of 5
0%
ar
s
0%
rs
0%
0,
00
1.
2.
3.
4.
98
 Based on the below Carbon Flux information, how many
years will it take for the carbon in the atm/ocean/bio to
double?
Answer: 40, 000/.0003 years = 133 million years
*1 Gt = 1015 grams
Net Carbon Flux
Atmosphere-Ocean-Biosphere
0.0297
Gt./yr A
B
0.0300
Gt./yr
Earth’s Crust
0.0003 Gt./yr
Long-Term CO2 Changes
Source: Berner, R. A., The rise of plants and their effect on
weathering and atmospheric
CO . Science, 276, 544-546.
MET 112 Global2Climate Change
100
Time Scale (Continued)
 The preceding operation would remove 40, 000
Gt. of carbon from the crust;
 This is only 0.1% of the carbon in the crust
 Thus, it is perfectly plausible that such an
imbalance could be sustained
101
MET 112 Global Climate Change
102
MET 112 Global Climate Change
Long-Term Carbon Cycle (Quantitative
Assessment)
AtmosphereOceanBiosphere
Carbon Content: 40, 000 Gt*.
Carbon Flux: 0.03 Gt/yr
Earth’s Crust
Carbon Flux: 0.03 Gt/yr
Carbon Content: 40, 000, 000 Gt.
*1 Gt = 1015 grams
MET 112 Global Climate Change
108