Noakhali Science & Technology University
Department of Fisheries and Marine Science
Course Title: Biological & Chemical Oceanography
Course Code: FIMS 4101, Year 4 Term 1
An Assignment On
Carbon Cycle
Submitted to Submitted by
Nazmun Naher Rima
Assistant Professor,
Department of Fisheries &
Marine Science, NSTU
Nazmul Haque Syekat
ROLL: ASH1802050M
Year 4 Term 1
Session: 2017-18
Date of Submission: 21th
August 2022

TABLE OF CONTENTS
SL NAME OF CONTENTS PAGE
1 Introduction: 1
2 What is the carbon cycle? 1
3 The Ocean Carbon Cycle
2
4 Steps of Carbon Cycle
3
5 Different Elements in Carbon Cycle 4
6 Importance of Carbon Cycle 7
7 Conclusion 7
8 References 7

1
Carbon Cycle
Introduction:
Carbon is an essential element for all life forms on Earth. Whether these life forms
take in carbon to help manufacture food or release carbon as part of respiration, the
intake and output of carbon is a component of all plant and animal life.
The carbon cycle is vital to life on Earth. Nature tends to keep carbon levels balanced,
meaning that the amount of carbon naturally released from reservoirs is equal to the
amount that is naturally absorbed by reservoirs. Maintaining this carbon balance
allows the planet to remain hospitable for life. Scientists believe that humans have
upset this balance by burning fossil fuels, which has added more carbon to
the atmosphere than usual and led to climate change and global warming.
What is the carbon cycle?
Carbon makes up the backbone of all life on Earth. It’s found in the cells of all living
things, is abundant in rocks and sediments, and is also found in the atmosphere and
ocean. But carbon doesn’t remain in one place.
Fig; The carbon cycle © Woods Hole Oceanographic Institution

2
Individual atoms move from one reservoir to another: between the atmosphere and the
oceans, from plants to animals to decomposers, to sediments and rock, and eventually
back to the atmosphere. This movement of carbon from one place to another, which
is caused by natural and human processes, is known as the carbon cycle.
The Ocean Carbon Cycle
Carbon exists in many forms in the global carbon cycle, including carbon dioxide (CO2)
and methane (CH4), two prominent greenhouse gases. CO2 exists naturally but is also
increasingly being emitted into the atmosphere through human activities like the
burning of fossil fuels. One quarter of this anthropogenic CO2 released into the
atmosphere is taken up by the ocean.
Fig: Shows how works carbon cycle in ocean
Some of this CO2 returns to the atmosphere, and some is exported to the deep ocean,
where the reservoir of carbon is 50 times larger than that stored in the atmosphere.
The ocean provides a vital service to our planet through this capacity to regulate
atmospheric CO2 levels and thereby limits climate change and its impacts. However,
a small change in the fluxes to the ocean carbon pool could impact the ocean’s storage
capacity and in turn impact atmospheric CO2 levels.

3
Steps of Carbon Cycle
Fig; Shows different steps associated with carbon cycle
The carbon cycle does not just happen in the terrestrial environment (that means ‘on
land’), it also happens in the marine environment (that means ‘in the sea’). The same
main processes exist in the marine carbon cycle:
1. Photosynthesis,
2. Respiration,
3. Consumption,
4. Decay and
5. Fossilisation.
In addition, you can see the blue arrows on the diagram that show the carbon flow between
the ocean and atmosphere as well as the process of physical mixing. Zooplankton play an
important role in removing carbon from the upper ocean and taking it to the deep
ocean.

4
Different Elements in Carbon Cycle
Fig; shows that how different elements interact each other to functioning carbon cycle [Source
“2007-2010 The University of Waikato” retrieved from www.sciencelearn.org.nz ]
1.Atmosphere
✓ Carbon in the atmosphere is mostly in the form of carbon dioxide with
some methane and hydrofluorocarbons. The amount of carbon dioxide in the
atmosphere is increasing.
2.Vegetation
✓ Plants store carbon as carbohydrates made from carbon dioxide from the
atmosphere. Land plants take up about a quarter of all carbon dioxide that
enters the atmosphere.
3.Soil and organic matter
✓ Soil contains a lot of carbon in the form of dead plant material and in the
many bacteria and other small organisms that live there.
4.Coal, oil, gas
✓ Carbon has been locked up in fossil fuels, built up from once-living things, for
millions of years.

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5.Sediments and sedimentary rock
✓ The carbon cycle overlaps the rock cycle. Ocean sediments and the rocks they
turn into contain huge amounts of carbon. This is mostly
in calcite and limestone.
6.Ocean surface
✓ Exchange of carbon dioxide between the ocean and the atmosphere takes place
at the surface.
7.Deep ocean
✓ Most of the carbon entering the ocean ends up in the deep ocean where it can
be carried by currents for hundreds of years or be lost in sediments.
8.Burning fossil fuels
✓ In fossil fuels, the carbon is stored in long-chain hydrocarbons, and then
through combustion with oxygen in our cars or in factories, the carbon is
converted to CO2, which is released to the atmosphere. And in addition, a
number of other byproducts are also produced through inefficiencies in
combustion like CO which are atmospheric pollutants.
9.Respiration
✓ Plants and animals release carbon dioxide into the atmosphere through the
process of respiration. Respiration releases energy from carbohydrates, with
carbon dioxide as a waste product.
10.Burning
✓ All the mass of all the trees that you’re seeing around is mostly coming from
atmospheric CO2. So, when we cut down forests and burn forests, then we are
releasing CO2 into the atmosphere.
11.Photosynthesis
✓ Plants take in carbon dioxide from the atmosphere during photosynthesis.
They use energy from the sun to combine the carbon dioxide and water to form
carbohydrates.

6
12.Decay
✓ In the soil, decomposers (such as microbes and soil animals) break down dead
plant material. As well as making nutrients available for living plants, this
process also releases carbon dioxide into the atmosphere.
13.Carbon dioxide exchange
✓ There is a constant vigorous exchange that is going two ways between the ocean
and the atmosphere. So once the CO2 goes into the ocean then that CO2 forms
carbonic acid, bicarbonate and carbonate ion, and it means that the ocean can
take up more CO2, so at present, there is about 60 times as much carbon in the
ocean as there is in the atmosphere.
14.Phytoplankton
✓ Plants take up CO2 – they essentially breathe it in and use it to build their
physical structures – and phytoplankton are basically teeny tiny microscopic
plants that live in the surface of the ocean, so essentially you have in the surface
of the ocean these little tiny microscopic plants are taking carbon from the
water and using it to build parts of their bodies.
15.Sinking sediment
✓ When phytoplankton die, many sink and take their carbon (calcium carbonate
shells) to form sediments at the bottom of the ocean. This is called a biological
pump, removing carbon from the ocean and atmosphere systems for long
periods of time.
16.Deep circulation
✓ Some carbon from phytoplankton is carried by deep ocean currents that might
not return it to the surface for hundreds of years.
17.Rock formation
✓ Sediments containing lots of calcium carbonate from shells can be turned into
rock over millions of years. This limestone rock can be pushed up to form land
by tectonic Earth movements. Some carbon trapped in the sediments forms gas
and oil.

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18.Weathering and run-off
✓ Rain slowly dissolves minerals from rocks – a process called weathering. These
minerals eventually get washed into the sea, where some minerals, such as
calcium carbonate, add to sediments at the bottom of the ocean.
Importance of Carbon Cycle
The carbon cycle describes the way the element carbon moves between the Earth's
biosphere, hydrosphere, atmosphere, and geosphere. It is important because a stable
carbon cycle is essential to life on Earth. Maintaining a carbon balance allows the
planet to remain habitable for life. Without it, life on Earth as we know it would be in
danger of being destroyed.
One form carbon take is the greenhouse gas carbon dioxide, CO2. Increased levels of
carbon dioxide insulate the Earth, causing temperatures to rise. Understanding how
carbon dioxide is absorbed and released helps us understand the climate and
predict global warming.
Conclusion
The oceans play a particularly important role in the carbon cycle. Surface waters
exchange gases with the atmosphere, absorbing and releasing carbon dioxide, oxygen,
and other gases. Plant-like phytoplankton living in the ocean convert carbon dioxide
into sugars that feed marine ecosystems. When marine animals die, their bodies may
sink into the depths, where the carbon they contain either gets dissolved back in to
deep waters, or a smaller fraction settles to the seafloor where it is covered in sediment
and locked away for centuries. Such processes may eventually create coal or oil
deposits deep underground.
References:
Bauer, J.E., W.-J. Cai, P.A. Raymond, T.S. Bianchi, C.S. Hopkinson, & P.A. Regnier.
The changing carbon cycle of the coastal ocean. Nature, vol. 504.2013. doi:
10.1038/nature12857.
NASA. Carbon cycle. https://science.nasa.gov/earth-science/oceanography/ocean-
earth-system/ocean-carbon-cycle. Accessed on February 18. 2021.
NOAA. What is the carbon cycle? https://oceanservice.noaa.gov/facts/carbon-
cycle.html. Accessed on February 18, 2021.