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The Carbon Cycle

Tracking Carbon Through the Earth System

H2CO3

Organic Inorganic

CO2

diffusion

CO2+H2OàH2CO3

CO2 CO2

Short Term

Long Term

weath

ering

CH4

decomposition

weatheringH2CO3

photosynthesisrespiration

uplift

rock formation

volc

anis

m

H2CO3àH++HCO3-

sedimentation sedimentationdissolution

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Inorganic Carbon ReservoirsGt = Gigaton

=109 metric tons;= 2679 x 109 pounds

Some More DefinitionsIonsAtoms or molecules having either more or less electrons (-) than protons (+)giving them a positive or negative electrical charge.

CationPositively charged ion, missing electrons (H+, Na+, Ca+2).

AnionNegatively charged ion, extra electrons (Cl-, CO3

-2)..

pH-log[H+], tells how acidic or basic a solution is.

AcidA solution with a high concentration of H+, pH < 7.

BaseA solution with a low concentration of H+, pH > 7.

Chemical equilibrium A steady state for a chemical reaction that can move in both directions.

DissociationMolecules breaking appart into ions when dissolved in water.

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Some More DefinitionsSourceInflow into a reservoirSinkOutflow from a reservoirFluxInflow, outflow; source, sink

HCl

HCl

HClHCl

H+

Cl-

Cl-

Cl-

H+

H+

Acid Water

Acids in Water Solutions

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Acid-Base Scale: pH = -log[H+]

Chemical Equations

H2CO3 H+ + HCO3-

productsreactants

H2O + CO2 H2CO3

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Equations to Know

Carbonic acid production from carbon dioxideand water:

CO2 + H2O H2CO3

H2CO3

Organic Inorganic

CO2

diffusion

CO2+H2OàH2CO3

CO2 CO2

Short Term

Long Term

weath

ering

CH4

decomposition

weatheringH2CO3

photosynthesisrespiration

uplift

rock formation

volc

anis

m

H2CO3àH++HCO3-

sedimentation sedimentationdissolution

6

DiffusionCO

2 CO2

Diffusion

CO2 + H2O <-----> H2CO3

Carbonate Chemistry

1

Water

CO2 DiffusionAtmosphere - Ocean Equilibrium

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What Happens When CO2Dissolves in Water?

Carbonic acid

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-1 2H+ + CO3

-2

Bicarbonate ion

Hydrogenion

Carbonate ion

Summary

• Removes dissolved CO2 from ocean• Increases acidity of ocean• Allows for further diffusion of CO2 from atmos-

phere into ocean.

Carbonate Ion Formation H2CO3 H

+ + HCO3-2 2H+ + CO3

-2

Acid FormationCO2 + H2O H2CO3

DiffusionCO2(atmos) CO2(ocean)

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H2CO3

Carbonate Weathering:CaCO3 + H2CO3 à Ca+2 + 2HCO3

-

Ca2+, SiO2, HCO3- to ocean

Silicate Weathering:CaSiO3 + 2H2CO3 à Ca2+ + 2HCO3

- + SiO2 + H2O

Weathering2

3 Carbonate Mineral Deposition

Calcium Carbonate precipitates in the OceanCa2+ + 2HCO3

-à CaCO3 + H2CO3by organisms that make shells & skeletal structure

Ca+2

CO3-2

Increases acidity of Ocean

In shallow ocean collectsin sediments limestone

In deep ocean is dissolved by more acidic waterDecreases acidity of Ocean

CaCO3

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4

CaCO3

Long-term Inorganic Cycle

Sedimentary Rockup

lift

volc

anis

mBalance of the Inorganic Carbon Cycle

Carbonateweathering

Carbonateprecipitation

Buried CO3-2 returns to atmosphere

via solid Earth processes.

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CO2+H2O --> H2CO3CaSiO3 +2H2CO3-->Ca2+ + 2HCO3

- + SiO2 + H2OCa2

+ + 2HCO3- --> CaCO3 + H2CO3

CaSiO3 + CO2 --> CaCO3 + SiO2

Atmospheric CO2 should go away in about a million years, but it has not. Why not?

Net: C goes fromatmos to ocean floor.

Togetherthese 3mechanismsremove CO2from atmos .

Silicate

weathering

Balance of the Inorganic Carbon Cycle

Carbonate-Silicate Cycle

Carbonate-Silicate weathering is “balanced” by Carbonate Metamorphism

CaCO3+ SiO2àCaSiO3 + CO2

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Carbonate-silicate Cycle

Silicate Weathering Feedback

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H2CO3

Organic Inorganic

CO2

diffusion

CO2+H2OàH2CO3

CO2 CO2

Short Term

Long Term

weath

ering

CH4

decomposition

weathering

H2CO3

photosynthesisrespiration

uplift

rock formation

volc

anis

m

H2CO3àH++HCO3-

sedimentation sedimentationdissolution

Inorganic Carbon Cycle ProcessesWhat causes local imbalance in

ocean-atmosphere CO2 flux?

• Photosynthesis: Where plants actively take up CO2, ocean uptake may dominate.

• Upwelling: “Old” water contains lots of CO2. Where up-welling occurs, CO2 release to the atmosphere may dominate.

• Precipitation of CaCO3: In the open ocean, some phytoplankton make shells. At the same time they do photosynthesis. For every one CO2 they produce by precipitation, they take up 4 CO2’s by photosynthesis (See Color Figure 7-8b), ocean uptake may dominate.

Answer: Variations in productivity and upwelling.

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Ocean-Atmosphere CO2 Diffusion

Reservoir = Atmosphere

in in

outout

out

Inorganic Carbon Cycle

WeatheringSedimentationDiffusion

Short term

Long term

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Earth’s Carbon Reservoirs

0.08 Gton/yr

~7Gton/yr

increase inflowby ~ 6%

Equations to Know

• Photosynthesis:CO2 + H2O à CH2O + O2

• Respiration:O2 + CH2O à CO2 + H2O

2CH2O àCO2 + CH4

• Carbonic acid production from carbon dioxideand water:CO2 + H2O ßà H2CO3