THE CARBON CYCLE CHAPTER 8 GEO 307 DR. GARVER 5/5/2015.

THE CARBON CYCLE

CHAPTER 8

GEO 307DR. GARVER

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RISE IN ATMOSPHERIC CARBON DIOXIDE FROM 1744 TO 1992 (INCREASE IS EXPONENTIAL)

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CARBON CYCLE

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ARCHER FIG. 8.1

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Fraction of Earth’s C

50x C of atm Several times more C than atm

Lots of C!!

Mostly limestone sedimentary rocks

1. C exists in a range of forms

Most stable as CO2 and CaCO3

2. Photosynthesis stores energy by producing

organic carbon

3. Atmosphere contains only a fraction of carbon

4. Biosphere has several more times carbon than

atm

Seasonal signal seen

5, Oceans contains 50x C of atmosphere

Responsible for large changes in CO2 over 100,000 year

time scales

6. Weathering of rock consumes CO2 on timescales

of millions of years

FROM ARCHER FIG. 8.1

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C.________%________

A._________

%______

B._________

%_______

D.___________

%___________

E._______

G.________

F.______

CARBON SINKS (RESERVOIRS)

Reservoir that uptakes a

chemical element from another

part of its cycle.

Each year hundreds of billions of

tons of carbon, in the form of

CO2, are absorbed by oceans,

soils, plants.

SINKS

(1) biosphere - living and dead material

+organic matter in soils

(2) atmosphere – CO2

(3) lithosphere - fossil fuels, sedimentary

rocks

(4) Oceans - dissolved CO2 & calcium

carbonate (shells) in marine organisms.

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CARBON FLUXES

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CARBON FLUXES

Plants - CO2 from atmosphere.

CO2 enters ocean by diffusion.

Used to produce shells (coral, clams)

Organisms die, shells sink to the ocean

floor.

After long periods of time, deposits are

physically and chemically altered into

sedimentary rocks.

CARBON FLUXESCarbon from ecosystems as CO2 by respiration.

Respiration - both plants and animals -

breakdown of carbon-based organic

molecules into CO2

detritus food chain - decomposition of organic

matter.

Natural ecosystems store between 20 to

100x more CO2 than agricultural land.

CARBON ON EARTH --- START HERE WEEK 9

Now let’s back up to the beg. of the chapter

and think about Carbon in more detail…

p. 89 Backbone for constructing the machinery

of life & provides the means of storing

energy.

Photosynthesis – converts suns energy into

carbon biomolecules.

Energy then used by plant, or animal that eats

it.

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CARBON ON EARTH

Over geologic timescales, carbon stores

energy on a planetary scale.

“Charges up” the biosphere with a store of

biomolecules like a giant battery.

Extracting energy from fossil fuels harvests

ancient energy stores of the biosphere.

Rearranges the distribution of carbon

among its reservoirs (sinks) on Earth.04/18/23

CARBON

‘Rich, wondrous chemistry’

Carbon chemistry is kept highly organized

within living things.

Then, after life is finished carbon left in soils,

sediments, and rocks forms itself into

humic acids or kerogen.

The number of configurations of carbon is

infinite.

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HUMIC ACIDS/HUMIC SUBSTANCES

Major constituents of soil organic matter

Precursors of fossil fuels

found in peat, coal, streams/lakes, ocean

Created by microbial degradation of dead

plant and animal material.

Most stable part of organic matter in soils,

can persist for tens, hundreds or even

thousands of years.04/18/23

KEROGEN

Mixture of organic chemical

compounds that make up a portion

of the organic matter in

sedimentary rocks.

crude oil or natural gas,

hydrocarbons

oil shale deposits

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To understand carbon and

all its forms, need to think

about oxidation.

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REDUCTION-OXIDATION CHEMISTRY

‘Oxidation’ - measure of the surplus or deficit of

electrons.

Chemical reaction in which atoms have their oxidation

number changed.

Interaction between oxygen molecules and all the

different substances they may contact, from

metal to living tissue.

Most elements have more than one possible Most elements have more than one possible

oxidation state.oxidation state.04/18/23

P. 90 REDUCTION-OXIDATION CHEMISTRY

Oxidized Intermediate Reduced

Simplest example

CO2 CH20 CH4

C oxidation state

+4 0 -4

General Category

Inorganic carbon

Carbohydrates Hydrocarbons

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‘Oxidation’ is a measure of the surplus or deficit

of electrons.

Oxygen atoms each want to steal 2 electrons.

Gives it its most stable electronic configuration.

CO2 – oxygen takes 4 electrons (+4)

CH4 – hydrogen atoms each give 1 electron to

carbon (-4)

CH2O – C gains 2 from H but give 2 to O

C has many oxidation states so we group them C has many oxidation states so we group them

into families.into families.04/18/23

1. Inorganic (oxidized) carbon - Most of the C on Most of the C on

EarthEarth

Most stable form;

CaCO3 (Limestone)

Dissolved in oceans

2. Organic Carbon (reduced & intermediate) -

Hydrocarbons

Oil

Natural gas

3. Carbohydrates (life is comprised of C in the

intermediate state)

Sugars

Life on Earth is based on the ‘nifty trick’ of

harvesting energy from the sun and

storing it by creating organic carbon from

inorganic (oxidized) carbon.

CO2 + H2O + energy CH2O + O2

Photosynthesis – forward direction of eqn (plants)

Respiration – backward direction of eqn (consumers)

PHOTOSYNTHESIS

Serves 2 purposes in the biosphere:uses carbon in the oxidation state

stores energy from the sun in the form of organic carbon

Nearly all of the organic carbon Nearly all of the organic carbon

produced by photosynthesis is produced by photosynthesis is

respired sooner or later.respired sooner or later.Peat deposits may hold organic carbon for thousands of

years.

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But, on geologic scales, only organic

carbon that ends up in ocean

sediments escapes degradation back

to CO2

Earth has built up sizable pool of

carbon in the reduced form of ocean

sediments and sedimentary rocks

(former ocean sed. on land).

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FIG. 8.1

CO2 in atm – tiniest fraction of all C on Earth

Atm contains 700 gigatons of CGton = 1 billion (109) metric tons

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• Other sinks have more C• All ‘breathe’ CO2, causing atm CO2 to vary naturally.

• Timescales – 1 yr. to millions.

THE LAND BREATHES

2 forms of carbon associated with the landscape;

1. Terrestrial biosphere (plants/animals)

-similar in size to atm

2. Soil Carbon Pool

-more C than in living biosphere

-highly varied place to place

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•Living CarbonAnnual cycle

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THE OCEAN BREATHESLarger sink than land surface or

atm.Dissolved inorganic Cnot only dead, it’s oxidized.CO2, H2CO3 (carbonic acid)Dissolved organic carbondetritusLiving CFish, algaeFlux – similar to landC is released from water in some areas and dissolves in others

EVEN THOUGH OCEAN AND LAND FLUXES ARE SIMILAR…Oceans don’t effect the CO2 levels of atm

as quickly as biosphere can.Atm absorbs CO2 from oceans until the

rate in and out balances.It takes hundreds of years for this equilibrium, because the oceans circulate so slowly.

Glacial/interglacial cycle are an example of how oceans effect atm CO2

Ice age every 150 million yearsInterglacial last 10,000 years

Very different timescale than atm/land flux!!

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Ice core data shows changes in CO2

Glacial intervals 180 – 200 ppm CO2

Interglacial 260 – 280 ppm (preindustrial)

No one is sure why the CO2 cycles

up and down, but the oceans are

thought to be the source.

THE ROCKS BREATHESedimentary rock carbon pool largest Limestone (CaCO3) + some organic C (Kerogen)

Fossil Fuels

Flux is very small!!But sink is HUGE!500x atm/land combined

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UREY REACTION

CaSiO3 + CO2 CaCO3 + SiO2

Silicate rocks are weathered to produce sedimentary rocks.

Flux is extremely smallBut, if degassing stopped CO2 would

be gone from atm in a few hundred thousand years.

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Takes CO2 out of atm

Puts CO2 back into atm

THE CARBONATE-SILICATE CYCLE

Also known as the Urey Reaction

Rainfall acts to "wash" CO2 out of the

atmosphere in the form of carbonic acid:

CO2 (gas) + H2O (liquid) --> H2CO3 (carbonic acid)

The carbonic acid weathers the rocks on the

Earth's surface, releasing ions of calcium (Ca++)

and bicarbonate (HCO-3) into the oceans.

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These combine into calcium carbonate (CaCO3)

on the sea floor either through

formation of carbonate rocks

living organisms making carbonate shells

The calcium carbonate is eventually subducted

down into the Earth (via plate tectonics),

where high temps and pressures convert it

back to CO2 gas.

CO2 gas gets outgassed from volcanos back into

the atmosphere.

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TAKE HOME POINTS

Most stable form of C is oxidized as COMost stable form of C is oxidized as CO22 or or

CaCOCaCO33

Photosynthesis stores energy by producing organic C

There is less C in atm than any other sink.

Land and ocean sinks effect atm C, seasonally

for land, 100,000 year scale for oceans.

Flux from sed. rock sink is small (weathering)

though size of this sink is the largest.

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EXERCISE #3 ZERO DEG

EXERCISE #3 10 DEG

EXERCISE #3 23.5 DEG

EXERCISE #3 45 DEG

EXERCISE #3 90 DEG

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EXERCISE #3 – 420 WM2 AT EQUATOR = 320 K

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EXERCISE #3 – 420 WM2 AT EQUATOR WITH 10% ALBEDO = 347 K

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EXERCISE #3 HEAT TRANSPORT PART C – HIGH LATITUDES

EXERCISE #3

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