the carbon cycle chapter 8 geo 307 dr. garver 5/5/2015
TRANSCRIPT
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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