biogeochemical cycle

1. CARBON CYCLE

3. What is a Carbon Cycle?
 The carbon cycle is the biogeochemical cycle by
which carbon is exchanged among
the biosphere, pedosphere, geosphere, hydrosphere,
and atmosphere of the Earth. Carbon is the main component
of biological compounds as well as a major component of
many minerals such as limestone. Along with the nitrogen
cycle and the water cycle, the carbon cycle comprises a
sequence of events that are key to make Earth capable of
sustaining life. It describes the movement of carbon as it is
recycled and reused throughout the biosphere, as well as
long-term processes of carbon sequestration to and release
from carbon sinks.
 The carbon cycle was discovered by Joseph
Priestley and Antoine Lavoisier, and popularized by Humphry
Davy.

4. Main Components
The carbon cycle is usually divided into the following major reservoirs of carbon
interconnected by pathways of exchange:
 The atmosphere
 The terrestrial biosphere
 The ocean, including dissolved inorganic carbon and living and non-living
marine biota
 The sediments, including fossil fuels, freshwater systems, and non-living
organic material.
 The Earth's interior (mantle and crust). These carbon stores interact with the
other components through geological processes.
 The carbon exchanges between reservoirs occur as the result of various
chemical, physical, geological, and biological processes. The ocean contains
the largest active pool of carbon near the surface of the Earth. The natural
flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and
sediments are fairly balanced so that carbon levels would be roughly stable
without human influence.

5. Atmosphere
 Carbon in the Earth's atmosphere exists in two main forms: carbon
dioxide and methane.
 Carbon dioxide of the atmosphere can be utilized for the production of
organic compounds by the reduction of carbon in the process of
photosynthesis. These organic compounds get oxidized during the
process of respiration releasing again carbon dioxide along with energy.
 Another source by means of which carbon dioxide is released is the
decomposition of carbon compounds by micro-organisms. Methane is a
common gas produced in marshes due to decomposition. It is released
in the atmosphere where it is ultimately changed into carbon dioxide.

6. Terrestrial Biosphere
 The terrestrial biosphere includes the organic carbon in all land-living
organisms, both alive and dead, as well as carbon stored in soils.
 Most carbon in the terrestrial biosphere is organic carbon, while about a third
of soil carbon is stored in inorganic forms, such as calcium carbonate.
 Carbon leaves the terrestrial biosphere in several ways. The combustion
or respiration of organic carbon releases it rapidly into the atmosphere. It can
also be exported into the ocean through rivers or remain sequestered in soils
in the form of inert carbon.

8. Lithosphere
 Lithosphere can also release carbon dioxide into
Earth’s atmosphere. This gas can be created by
chemical reactions in the Earth’s crust and mantle.
 Coal and petroleum when burnt release carbon
dioxide in the atmosphere. Burning of fossil fuels
adds about 5.9 billion tons of carbon to the
atmosphere.
 Volcanic eruptions as well as weathering of
carbonate rocks also releases carbon dioxide in the
atmosphere.

9. Oceans
 Oceans play an important role in regulating carbon dioxide content of the
atmosphere. The dissolved carbon in sea water helps to form carbonic acid-
dissolved liquid form of carbon, which converts carbonates into bicarbonates.
Large amounts of calcium in sea water also accelerates carbonate deposition.

11. Human Influence
 Since the industrial revolution, human activity has modified the carbon cycle
by changing its components' functions and directly adding carbon to the
atmosphere.
 The largest human impact on the carbon cycle is through direct emissions
from burning fossil fuels, which transfers carbon from the geosphere into the
atmosphere. The rest of this increase is caused mostly by changes in land-
use, particularly deforestation.
 Another direct human impact on the carbon cycle is the chemical process
of calcination of limestone for clinker production, which releases CO
2. Clinker is an industrial precursor of cement.
 Humans also influence the carbon cycle indirectly by changing the terrestrial
and oceanic biosphere

13. Why is Carbon Cycle Important?
 It is important for a few reasons:
i. Carbon is an essential element for all life, so understanding how it moves
helps us to understand biological processes and factors that influence them.
ii. One form carbon takes 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.
iii. The carbon cycle is tied to the availability of other elements and compounds.
For example, the carbon cycle is tied to the availability of oxygen in the
atmosphere. During photosynthesis, plants take carbon dioxide from the air
and used it to make glucose (stored carbon), while releasing oxygen.