Carbon Cycling Internal
The 4 subcycles
Atmosphere
The Earth’s Atmosphere
The Earth has a radius of some 6400 km. Ninety-nine percent of the earth's
atmosphere is contained within a layer approximately 50 km thick.
Life on earth inhabits a layer about 9 km thick, extending from a few
kilometres above sea level to a few kilometres below.
The atmosphere is a mixture of gases. Nitrogen and oxygen make up 99% of
air. 1% are "trace" gases, especially argon. Two other trace gases, carbon
dioxide and ozone, have a large impact on humans and all other life.
Water vapor is also present in small amounts. It absorbs heat from the Earth
and Sun.
The atmosphere is divided into four layers based on temperature: the
troposphere, stratosphere, mesosphere, and thermosphere.
We live in the troposphere.90% of our air is in this layer.
This is where all our weather occurs. Gravity keeps the atmosphere denser
close to the earth's surface
How it Works:
• Greenhouse gases act like an invisible blanket that traps just enough
energy, in a similar way that glass traps heat inside a greenhouse.
Without them the Earth's average surface temperature would be a cold,
18°C rather than the pleasant 15°C.
• The most important greenhouse gas is carbon dioxide. Carbon dioxide
has a huge effect on climate.
• Sunlight warms the Earth’s surface which then radiates out heat into the
atmosphere. Carbon dioxide molecules absorb some of this heat,
insulating the surface of the Earth from the cold of space and warming
the land and ocean.
When we talk about the greenhouse effect we mean the ENHANCED effect
which is caused by the increase of greenhouse gases from human sources.
Causes
The main sources of these emissions, particularly carbon dioxide, methane and
nitrous oxide, are:
• the combustion of large amounts of fossil fuels (producing CO2)
• deforestation (less trees mean that less CO2 is being mopped up) – often
to provide land for farming.
• decay (producing CO2 if oxygen is present, methane (CH4) if it is not.)
Not all of the Carbon Ends up in the Air
• Curiously, the increase in atmospheric CO2 is only about one-half of what
would have been expected from the amount of fossil fuel consumption
and forest burning.
• Where has the rest gone? Research has shown that increased CO2 levels
lead to increased net production by photoautotrophs. There is evidence
that at least some of the missing CO2 has been incorporated by
increased growth of forests, especially in North America;
• increased amounts of photoautotrophic plankton in the oceans;
• uptake by desert soils (mechanism as yet unknown).
Resources
DVD
• BBC Earth- the power of the planet
• BBC How the Earth made us
Oceans
The role of the oceans
The oceans have two important roles in helping keep a stable climate on Earth.
1. The great ocean currents play a very important part in maintaining a
steady climate. They transport huge quantities of heat in enormous
volumes of water.
The thermohaline current is a current that travels around the whole
world, mixing water from all the oceans and distributing heat. This
current has a huge influence on our climate.
Part of the current flows on the surface of the ocean and part flows far
under the surface in deep ocean basins. Cold dense water forms in the
Arctic Sea and around Antarctica and sinks. Warm less dense water from
other parts of the ocean moves to replace the sinking cold dense water.
This is what causes circulation forming the global thermohaline current
which spreads heat around the whole world.
2. Ocean circulation also influences the amount of carbon dioxide in the
atmosphere in 2 ways:
Waves on the surface of the ocean cause CO2 from the atmosphere to be
dissolved into the water. The colder the water, the more carbon dioxide
can be absorbed.
Tiny marine plants called phytoplankton, lock up carbon dioxide as part
of their bodies in the form of calcium carbonate shells. When they die
they sink to the bottom of the ocean and become part of the deep sea
sediments. Carbon dioxide is removed this way for several million years.
Photos of plankton that have shells made of calcium carbonate. When these
shells fall to the ocean bottom they become part of the sediment accumulating
there. The sediment gets compacted and limestone, which is calcium
carbonate, is formed.
Exercise
• Waves on the surface of the ocean cause _______ from the
atmosphere to be dissolved into the water. The colder the
water, the more
can be absorbed.
• Tiny marine plants called
_______________________________ lock up carbon dioxide
as part of their ___________ in the form of
__________________ ____________________ shells. When
they die they ___________ to the bottom of the ocean and
become part of the deep sea _______________________.
Carbon dioxide is removed this way for ________________
_____________________ years.
• In your own words write (in your book) about how carbon is
cycled in the oceans. Use these key words as part of your
answer: carbon dioxide, dissolved, carbonates,
photosynthesis, respiration, phytoplankton, sedimentation,
weathering, uplift (remember that phytoplankton is the sea’s
producer and carbon enters food chains in the ocean through
phytoplankton).
Biocycle
Plants & The Carbon Cycle
• Plants take in carbon dioxide and convert it to sugar which can
be stored until used for energy.
• This process is called photosynthesis.
• 6CO2 + 6H2O sunlight 6O2 + C6H12O6
• Plants release carbon dioxide as a waste product when they
convert their stored sugar to chemical energy.
• This process is called respiration.
Animals & The Carbon Cycle
• Animals eat carbon contained in animal and plant tissues and
release carbon dioxide as a waste product.
• This process is respiration.
• C6H12O6 + 6O2
6CO2 + 6H2O + energy
Aerobic vs Anaerobic Respiration
• Aerobic respiration is the process that takes place in presence
of oxygen (see above slide).
• Aerobic respiration is a high energy yielding process.
• Anaerobic respiration is the process of oxidation of molecules
in the absence of oxygen.
• Anaerobic respiration can occur in any of the following ways :
Glucose →Energy + Ethanol + Carbon dioxide (CO2)
Glucose →Energy + Lactic acid
• Glucose
methane and water + energy
Decay & The Carbon Cycle
• Decomposers release the carbon from dead plant and animal
tissues back into the atmosphere.
• Decomposers, when they break down dead organic matter,
release carbon dioxide into the air also. Decomposers are
essential because without them, all of the carbon on the planet
would eventually become locked up in dead carcasses.
Storage
In the bio cycle carbon is stored in leaves of plants. A percentage
passes to herbivores which store it in their tissues as muscle, fat and
glycogen. A percentage of this is then passed onto carnivores.
Decomposers return this carbon to the soil and air in the short term.
Long term storage can occur when the carbon stored in the lignin of
plants is buried and fossilised into coal.
Over millions of years fossil fuels may form from the buried
remains of plants and animals.
Agriculture
Agriculture affects the carbon cycle in the following ways:
1. Organic matter (mostly carbon) affects soil quality.
2. Crop residues create organic matter.
3. Manure adds organic matter.
Intensive tillage, burning fuels and the use of equipment adds CO2 to
the atmosphere.
No-till systems remove CO2.
Why no-till systems are good
1. Organic matter stays put.
2. Earthworms thrive.
3. Root channels remain undisturbed.
4. Prevents soil from crusting.
5. Water holding capacity improves.
6. Nutrient exchange improved.
7. Crop residues stay on surface.
8. Soil compaction reduced.
9. Long term crop production improved.
Geocycle/Lithocycle
Tectonic plates and volcanoes
• Earth is the only planet in our Solar System with tectonic plates.
Although plate tectonics involves the solid parts of the planet it
still has an important part to play in keeping the climate steady.
• The crust and the hard upper part of the mantle are broken
into giant rock plates called tectonic plates which float on the
softer, lower mantle. The core of Earth gives off an enormous
amount of heat which keeps the rock in the lower part of the
mantle soft and able to be moved along by giant convection
currents. This moves the tectonic plates so that sometimes
they collide and other times move apart from each other.
• When plankton with shells made of calcium carbonate die the
shells fall to the ocean bottom and become part of the
sediment accumulating there. The sediment gets compacted
and forms rock. Rock formed from compressed plankton shells
is called limestone. Both the shells and limestone is made of
calcium carbonate. This sediment will remain on the bottom of
the ocean forming deeper and deeper layers of limestone.
• Eventually much of the limestone will become subducted when
two tectonic plates collide, as is happening off the coast of the
North Island. The limestone is subducted deep into the ground
where it may be melted and become magma. Most of the
volcanoes around the world occur along boundaries between
tectonic plates.
• When magma is erupted from a volcano vast amounts of
carbon dioxide are released back into the atmosphere.
•
•
• 1. Carbon dioxide (and other greenhouse gases) keeps the
Earth at a pleasant, average temperature of about 15 degrees.
• 2. This warmth means that seawater evaporates, forming
clouds and rain.
• 3. Rain contains dissolved carbon dioxide (CO2) from the
atmosphere which makes it slightly acid. Therefore it dissolves
minerals from rocks which go into water such as rivers and
lakes.
• 4. The water and minerals are washed out to sea. The minerals
settle on the ocean floor or are made into the shells of tiny
plankton.
• 5. When plankton die their shells settle onto the ocean floor
where they become part of seafloor sediment. This sediment
forms thick layers which become compacted to form limestone.
• 6. When two tectonic plates collide one plate is often
subducted under the other. When this happens the limestone
will be subducted too.
• 7. When the subducted plate reaches a certain depth, the
limestone, along with other rock and sediment, will melt
forming magma.
• 8. Molten magma rises and is erupted from volcanoes as lava,
ash and gases, including vast amounts of carbon dioxide. The
carbon dioxide enters the atmosphere.
• This cycle is an extremely effective thermostat. When the
planet is warm, more water evaporates from the oceans and
rainfall increases. Because carbon dioxide is easily dissolved in
water, the extra rain speeds up the rate of atmospheric carbon
dioxide removal. This means that there is less greenhouse gas
in the atmosphere and therefore less heat can be trapped. The
planet is cooled. When it is cold, less water evaporates from
the oceans, rainfall decreases, allowing volcanic gases to build
up in the atmosphere, warming the planet.