The Carbon Cycle
Carbon Dioxide and Carbonate system
Why is it important?
1. CO2 regulates temperature of the planet
2. Important for life in the ocean
3. Regulates the pH of water
100 ppm
CO2
TEMPERATURE
1-6°C
Glacial-interglacial CO2 and temperature change
CO2
Temperature
80 ppm
CO2 changes in the last 300 yr
100 ppm
Industrial Revolution
CO2 changes in the last 50 yr: the Keeling curve
Oceans
Biosphere
Rock Weathering
How much CO2 can you sink in the ocean?
Chemical
Process that control CO2
absorption in the ocean
Biological
Physical
Carbon Cycle
Carbon Cycle
O2
CO2
pH
acid
basic
Dissolved Gases in the Ocean
Oxygen profile
O2
CO2
pH
The Carbonate System
sources of inorganic carbon
from dissolved CO2 gas

 H 2CO2 (aq) 


H 2O  CO2 ( gas) 



2


H   HCO3 (aq) 
2
H

CO

3 (aq )
from dissolution of Calcium Carbonate
2
3
2


CaCO ( s) 
Ca
(
aq
)

CO

3
CO2 in the ocean
pH   log10 [ H  ]
Total dissolved inorganic carbon
this is very small
 CO
2
not found in this form
 CO2 ( gas )  H 2CO2 (aq ) 
 HCO3 (aq )  CO32 (aq )
Total dissolved inorganic carbon
[ CO2 ]  [ HCO3 ]  [CO32 ]
(1)
(2)
formation and decomposition of organic matter
from dissolution of Calcium Carbonate
2
2


CaCO3 ( s) 
Ca
(
aq
)

CO

3
Total dissolved
inorganic carbon
Carbon Dioxide and Carbonate system
Carbonic Acid






H 2O  CO2 ( gas) 
H
CO
H

HCO
 2 3 

3

2


HCO3 
2
H

CO

3
Carbonate
Bicarbonate Ion
Distribution of Carbon species in water
+
[ HCO3 ]
[CO32 ]
-
[ HCO3 ]
[CO32 ]
CO2 changes in the last 50 yr
Oceans
Biosphere
Rock Weathering
What control the absorption of Carbon
Dioxide in the ocean?
The carbonate system chemistry in seawater
How can we measure it?
The concept of alkalinity, pH …
Def:
Alkalinity: is the net molar concentration, in chargeequivalents, of the cations of strong bases in excess of the
anions of strong acids
Strong base cations
A  [ Na  ]  [ K  ]  2[ Mg 2 ]  2[Ca 2 ] 
Strong acid anions

2

[
Cl
]

2[
SO
]

[
B
r
]

4
What happens to this balance?
Strong base cations
A  [ Na  ]  [ K  ]  2[ Mg 2 ]  2[Ca 2 ] 
Strong acid anions

2

[
Cl
]

2[
SO
]

[
B
r
]

4
Total dissolved inorganic carbon
[ CO2 ]  [ HCO3 ]  [CO32 ]
(2)
Calcium Carbonate dissolution and formation
2
2


CaCO3 ( s) 
Ca
(
aq
)

CO

3
-alkalinity
Total dissolved
inorganic carbon
+alkalinity
Alkalinity can be measured by titration

 H 2O  CO2 ( gas)
HCO (aq)  H 


3


 H 2O  CO2 ( gas)
CO32 (aq)  2 H  


3
2
3
A  [ HCO ]  2[CO ]
What happens if I add or remove CO2 by
photosynthesis and respiration?

 H 2O  CO2 ( gas)
HCO (aq)  H 


3


 H 2O  CO2 ( gas)
CO32 (aq)  2 H  


3
2
3
A  [ HCO ]  2[CO ]
Carbon Dioxide and Carbonate system
Carbonic Acid






H 2O  CO2 ( gas) 
H
CO
H

HCO
 2 3 

3

2


HCO3 
2
H

CO

3
Carbonate
Bicarbonate Ion
(1)
(2)
formation and decomposition of organic matter
Calcium Carbonate dissolution and formation
2
2


CaCO3 ( s) 
Ca
(
aq
)

CO

3
- acid
-alkalinity
+acid
Total dissolved
inorganic carbon
+alkalinity
Carbon Cycle
Ocean acidification: What corals are dying
to tell us
slides from Ken Caldeira
A cautionary tale
from 65Ma: the
Cretaceous-Tertiary
extinction
-huge comet blasts Yucatan
-releases S into atmosphere
-acid rain falls on ocean for
1-2 years
-ALL surface calcifiers die
for 2 million years!
We are changing CO2 rates faster than
the geologic past
CO32- is becoming a rare commodity
The surface ocean changes will lead
deep ocean changes
Corals are being pushed out of their
preferred saturation state
…and they are the most sensitive to
changes in saturation state