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1.4.19.24: The Carbon Cycle - Biology

1.4.19.24: The Carbon Cycle - Biology


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Learning Objectives

  • Discuss the carbon cycle and why carbon is essential to all living things

Carbon is the second most abundant element in living organisms. Carbon is present in all organic molecules, and its role in the structure of macromolecules is of primary importance to living organisms. Carbon compounds contain especially high energy, particularly those derived from fossilized organisms, mainly plants, which humans use as fuel. Since the 1800s, the number of countries using massive amounts of fossil fuels has increased. Since the beginning of the Industrial Revolution, global demand for the Earth’s limited fossil fuel supplies has risen; therefore, the amount of carbon dioxide in our atmosphere has increased. This increase in carbon dioxide has been associated with climate change and other disturbances of the Earth’s ecosystems and is a major environmental concern worldwide. Thus, the “carbon footprint” is based on how much carbon dioxide is produced and how much fossil fuel countries consume.

The carbon cycle is most easily studied as two interconnected sub-cycles: one dealing with rapid carbon exchange among living organisms and the other dealing with the long-term cycling of carbon through geologic processes. The entire carbon cycle is shown in Figure 1.

Click this link to read information about the United States Carbon Cycle Science Program.

The Biological Carbon Cycle

Living organisms are connected in many ways, even between ecosystems. A good example of this connection is the exchange of carbon between autotrophs and heterotrophs within and between ecosystems by way of atmospheric carbon dioxide. Carbon dioxide is the basic building block that most autotrophs use to build multi-carbon, high energy compounds, such as glucose. The energy harnessed from the sun is used by these organisms to form the covalent bonds that link carbon atoms together. These chemical bonds thereby store this energy for later use in the process of respiration. Most terrestrial autotrophs obtain their carbon dioxide directly from the atmosphere, while marine autotrophs acquire it in the dissolved form (carbonic acid, H2CO3). However carbon dioxide is acquired, a by-product of the process is oxygen. The photosynthetic organisms are responsible for depositing approximately 21 percent oxygen content of the atmosphere that we observe today.

Heterotrophs and autotrophs are partners in biological carbon exchange (especially the primary consumers, largely herbivores). Heterotrophs acquire the high-energy carbon compounds from the autotrophs by consuming them, and breaking them down by respiration to obtain cellular energy, such as ATP. The most efficient type of respiration, aerobic respiration, requires oxygen obtained from the atmosphere or dissolved in water. Thus, there is a constant exchange of oxygen and carbon dioxide between the autotrophs (which need the carbon) and the heterotrophs (which need the oxygen). Gas exchange through the atmosphere and water is one way that the carbon cycle connects all living organisms on Earth.

The Biogeochemical Carbon Cycle

The movement of carbon through the land, water, and air is complex, and in many cases, it occurs much more slowly geologically than as seen between living organisms. Carbon is stored for long periods in what are known as carbon reservoirs, which include the atmosphere, bodies of liquid water (mostly oceans), ocean sediment, soil, land sediments (including fossil fuels), and the Earth’s interior.

As stated, the atmosphere is a major reservoir of carbon in the form of carbon dioxide and is essential to the process of photosynthesis. The level of carbon dioxide in the atmosphere is greatly influenced by the reservoir of carbon in the oceans. The exchange of carbon between the atmosphere and water reservoirs influences how much carbon is found in each location, and each one affects the other reciprocally. Carbon dioxide (CO2) from the atmosphere dissolves in water and combines with water molecules to form carbonic acid, and then it ionizes to carbonate and bicarbonate ions:

The equilibrium coefficients are such that more than 90 percent of the carbon in the ocean is found as bicarbonate ions. Some of these ions combine with seawater calcium to form calcium carbonate (CaCO3), a major component of marine organism shells. These organisms eventually form sediments on the ocean floor. Over geologic time, the calcium carbonate forms limestone, which comprises the largest carbon reservoir on Earth.

On land, carbon is stored in soil as a result of the decomposition of living organisms (by decomposers) or from weathering of terrestrial rock and minerals. This carbon can be leached into the water reservoirs by surface runoff. Deeper underground, on land and at sea, are fossil fuels: the anaerobically decomposed remains of plants that take millions of years to form. Fossil fuels are considered a non-renewable resource because their use far exceeds their rate of formation. A non-renewable resource, such as fossil fuel, is either regenerated very slowly or not at all. Another way for carbon to enter the atmosphere is from land (including land beneath the surface of the ocean) by the eruption of volcanoes and other geothermal systems. Carbon sediments from the ocean floor are taken deep within the Earth by the process of subduction: the movement of one tectonic plate beneath another. Carbon is released as carbon dioxide when a volcano erupts or from volcanic hydrothermal vents.

Carbon dioxide is also added to the atmosphere by the animal husbandry practices of humans. The large numbers of land animals raised to feed the Earth’s growing population results in increased carbon dioxide levels in the atmosphere due to farming practices and the respiration and methane production. This is another example of how human activity indirectly affects biogeochemical cycles in a significant way. Although much of the debate about the future effects of increasing atmospheric carbon on climate change focuses on fossils fuels, scientists take natural processes, such as volcanoes and respiration, into account as they model and predict the future impact of this increase.

Learning Objectives

This video talks about two of the biogeochemical cycles: carbon and water. The hydrologic cycle describes how water moves on, above, and below the surface of the Earth, driven by energy supplied by the sun and wind. The carbon cycle does the same . for carbon!

A YouTube element has been excluded from this version of the text. You can view it online here: pb.libretexts.org/bionm2/?p=600


Carbon Cycle, Nitrogen Cycle, Phosphorus and Sulphur Cycle

Based on the replacement period, a nutrient cycle is referred to as Perfect or Imperfect cycle.

  • A perfect nutrient cycle is one in which nutrients are replaced as fast as they are utilized.
  • Most gaseous cycles are generally considered as perfect cycles.
  • In contrast sedimentary cycles are considered relatively imperfect, as some nutrients are lost from the cycle and get locked into sediments and so become unavailable for immediate cycling.

Based on the nature of the reservoir, a nutrient cycle is referred to as Gaseous or Sedimentary cycle

  • Gaseous Cycle: the reservoir is the atmosphere or the hydrospherewater cycle, carbon cycle, nitrogen cycle , etc. and
  • Sedimentary Cycle: the reservoir is the earth’s crust (soluble elements mostly found in earth’s crust) — phosphorous cycle, sulphur cycle, calcium cycle, magnesium cycle etc.

Carbon Cycle (Gaseous Cycle)

  • Carbon is a minor constituent of the atmosphere as compared to oxygen and nitrogen.
  • However, without carbon dioxide life could not exist because it is vital for the production of carbohydrates through photosynthesis by plants.
  • It is the element that anchors all organic substances from coal and oil to DNA (deoxyribonucleic acid: the compound that carries genetic information).
  • Carbon is present in the atmosphere, mainly in the form of carbon dioxide (CO2).
  • Carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms.
  • Carbon from the atmosphere moves to green plants by the process of photosynthesis, and then to animals.
  • By process of respiration and decomposition of dead organic matter, it returns to the atmosphere. It is usually a short term cycle.
  • Some carbon also enters a long term cycle. It accumulates as un-decomposed organic matter in the peaty layers of marshy soil or as insoluble carbonates in bottom sediments of aquatic systems which take a long time to be released.
  • In deep oceans, such carbon can remain buried for millions of years till geological movement may lift these rocks above sea level.
  • These rocks may be exposed to erosion, releasing their carbon dioxide, carbonates and bicarbonates into streams and rivers.
  • Fossil fuels such as coals, oil and natural gas etc. are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When they are burned the carbon stored in them is released back into the atmosphere as carbon dioxide.
Q. Consider the following:

Which of the above add carbon dioxide to the carbon cycle on Earth?

  1. 1 and 4 only
  2. 2 and 3 only
  3. 2,3 and 4 only
  4. 1, 2, 3 and 4
  • Photosynthesis takes out CO2 from the carbon cycle. Rest all add CO2.
Q. Which one of the following is the process involved in photosynthesis?
  1. Potential energy is released to form free energy
  2. Free energy is converted into potential energy and stored
  3. Food is oxidized to release carbon dioxide and water
  4. Oxygen is taken, and carbon dioxide and water vapour are given out
  • Potential energy is released to form free energy (false – sun’s free energy is converted into potential energy in photosynthesis)
  • Food is oxidized to release carbon dioxide and water (false – oxygen is released and not carbon dioxide)
  • Oxygen is taken, and carbon dioxide and water vapour are given out (false – CO2 is taken, and oxygen is given out)
  • Answer: b) Sunlight (free energy) is converted into carbohydrates (potential energy) using water and carbon dioxide. Oxygen is released in the process.

Nitrogen Cycle (Gaseous Cycle)

  • Apart from carbon, hydrogen and oxygen, nitrogen is the most prevalent element in living organisms.
  • Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls and many of the vitamins (explained in Biology NCERT).
  • Plants compete with microbes for the limited nitrogen that is available in the soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
  • Nitrogen exists as two nitrogen atoms (N2) joined by a very strong triple covalent bond (N ≡ N).
  • In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O).
  • Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.

Nitrogen Fixing – Nitrogen to Ammonia (N2 to NH3)

  • There is an inexhaustible supply of nitrogen in the atmosphere, but the elemental form cannot be used directly by most of the living organisms.
  • Nitrogen needs to be ‘fixed’, that is, converted to ammonia, nitrites or nitrates , before it can be taken up by plants.
  • Nitrogen fixation on earth is accomplished in three different ways:
  1. By microorganisms (bacteria and blue-green algae),
  2. By man using industrial processes (fertiliser factories) and
  3. To a limited extent by atmospheric phenomena such as thunder and lighting.
  • Certain microorganisms are capable of fixing atmospheric nitrogen into ammonia (NH3) and ammonium ions (NH4+).
  • Ammonia (NH3) is a molecule consisting of nitrogen and hydrogen, while ammonium (NH4+) is an ion of ammonia that is formed by accepting a hydrogen ion.
  • The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes. Such microbes are called N2-fixers. These include:
  • free-living nitrogen fixing bacteria (non-symbiotic nitrogen-fixing bacteria or nitrogen-fixing soil bacteria) (e.g. aerobic Azotobacter and Beijemickia anaerobic Clostridium and Rhodospirillum ),
  • symbiotic nitrogen-fixing bacteria (e.g. Rhizobium ) living in association with leguminous plants and non-leguminous root nodule plants and
  • some cyanobacteria (a major source of nitrogen fixation in oceans) (blue-green algae. E.g. Nostoc, Anabaena, Spirulina etc.).
  • Leguminous: denoting plants of the pea family (Leguminosae), typically having seeds in pods, distinctive flowers, and root nodules containing nitrogen-fixing bacteria.

Nitrification – Ammonia to Nitrates

  • Ammonium ions can be directly taken up as a source of nitrogen by some plants.
  • Others absorb nitrates which are obtained by oxidising ammonia and ammonium ions.
  • Ammonia and ammonium ions are oxidised to nitrites or nitrates by two groups of specialized bacteria.
  • Ammonium ions are first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococcus .
  • The nitrite is further oxidized to nitrate with the help of the bacterium Nitrobacter .
  • These steps are called nitrification. These nitrifying bacteria are chemoautotrophs (they use inorganic chemical energy sources to synthesise organic compounds from carbon dioxide).
  • The nitrate thus formed is absorbed by plants and is transported to the leaves.
  • In leaves, it is reduced to formammonia that finally forms the amine group of amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem.
  • Nitrification is important in agricultural systems , where fertiliser is often applied as ammonia.
  • Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia.
  • Nitrification also plays an important role in the removal of nitrogen from municipal wastewater.
  • The conventional removal is nitrification, followed by denitrification.

Ammonification – Urea, Uric Acid to Ammonia

  • Living organisms produce nitrogenous waste products such as urea and uric acid (organic nitrogen).
  • These waste products, as well as dead remains of organisms, are converted back into inorganic ammonia and ammonium ions by the bacteria. This process is called ammonification.
  • Some of this ammonia volatilizes and re-enters the atmosphere, but most of it is converted into nitrate by soil bacteria.

Denitrification – Nitrate to Nitrogen

  • Nitrate present in the soil is reduced to nitrogen by the process of denitrification.
  • In the soil as well as oceans there are special denitrifying bacteria ( Pseudomonas and Thiobacillus ), which convert the nitrates/nitrites to elemental nitrogen.
  • This nitrogen escapes into the atmosphere, thus completing the cycle.
  • Most of the ammonia escapes into the atmosphere. Rest is Nitrified (Step 2) to nitrates.
  • Some of the nitrates is available for plants. Rest is Denitrified (Step 4).
  • The amount of nitrogen fixed by man through the industrial process has far exceeded the amount fixed by the Natural Cycle.
  • As a result, nitrogen fixed by man has become a pollutant which can disrupt the balance of nitrogen. It may lead to Acid rain, Eutrophication and Harmful Algal Blooms .
Q. Which of the following adds/add nitrogen to the soil?

Select the correct answer using the codes given below.

  • All the above three adds to the nitrogen cycle.
  • Burning coal releases CO, CO2, sulphur dioxide and oxides of nitrogen – air pollutants.
  • Oxides of nitrogen fall on earth as acid rain. Acidic rain is a complex mixture of nitrous, nitric, sulphurous and sulfuric acids which all combine to lower the pH.
  • But, the question asks, “Which of the following adds/add nitrogen to the soil?”
  • Animal waste like urea, uric acid and death of vegetation add nitrogen in the form of nitrates directly into the soil.
  • Coal combustion adds nitrogen to the atmosphere and from there it falls back to earth in the form of acid rain and acid rain adds nitrogen to the soil.
  • “The release of nitric oxides into the air in large quantities causes smog and acid rain. The increase in nitrogen and nitrous oxide is caused by automobiles, power plants and a wide variety of industries.”
  • And also http://chemistry.elmhurst.edu/vchembook/307nitrogen.html says:
  • “Nitrogen will only react with oxygen in the presence of high temperatures and pressures found near lightning bolts and in combustion reactions in power plants or internal combustion engines. Nitric oxide, NO, and nitrogen dioxide, NO2, are formed under these conditions. Eventually, nitrogen dioxide may react with water in the rain to form nitric acid, HNO3. The nitrates thus formed may be utilised by plants as a nutrient (so, soil gets nitrogen from acid rain).”
  • From the above explanation, it is clear that burning of coal by man adds nitrogen to soil but indirectly though acid rain.

Answer: Official UPSC Key says the answer is c) 1 and 3 only.

Q. Consider the following:

Which of the above is/are the emission/emissions from coal combustion at thermal power plants?

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
  • Burning coal releases CO, CO2, sulphur dioxide and oxides of nitrogen.
Q. What can be the impact of excessive/inappropriate use of nitrogenous fertilisers in agriculture?
  1. Proliferation of nitrogen-fixing microorganisms in soil can occur.
  2. Increase in the acidity of soil can take place.
  3. Leaching of nitrate to the ground-water can occur.

Select the correct answer using the code given below.

  • Nitrification is important in agricultural systems, where fertiliser is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble.
  • Agricultural fertilisation and the use of nitrogen-fixing plants also contribute to atmospheric NOx, by promoting nitrogen fixation by microorganisms. Excess NOx leads to acid rain. Acid rain lowers pH of the soil (increase in acidity of soil)
  • The legume-rhizobium symbiosis is a classic example of mutualism — rhizobia supply ammonia or amino acids to the plant and in return receive organic acids as a carbon and energy source.
  • So, excessive/inappropriate use of nitrogenous fertilisers can make the plants independent of both symbiotic and free-living nitrogen fixers. Fixers don’t get the food from the plants due to a broken relationship and other factors. So, their population decreases.

Phosphorus Cycle (Sedimentary cycle)

  • Phosphorus plays a central role in aquatic ecosystems and water quality.
  • Unlike carbon and nitrogen, which come primarily from the atmosphere, phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and mining activities.
  • This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants (phytoplankton) in lakes (leads to eutrophication) .
  • The main storage for phosphorus is in the earth’s crust.
  • On land, phosphorus is usually found in the form of phosphates.
  • By the process of weathering and erosion, phosphates enter rivers, streams and finally oceans.
  • In the ocean, phosphorus accumulates on continental shelves in the form of insoluble deposits.
  • After millions of years, the crustal plates rise from the seafloor and expose the phosphates on land.
  • After more time, weathering will release them from rock, and the cycle’s geochemical phase begins again.

Sulphur Cycle (Sedimentary cycle)

  • The sulphur reservoir is in the soil and sediments where it is locked in organic ( coal, oil and peat ) and inorganic deposits ( pyrite rock and sulphur rock ) in the form of sulphates, sulphides and organic sulphur.
  • It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.
  • The sulphur cycle is mostly sedimentary except two of its compounds, hydrogen sulphide (H2S) and sulphur dioxide (SO2), which add a gaseous component.
  • Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels (coal, diesel etc.), from the surface of the ocean and gases released by decomposition .
  • Atmospheric hydrogen sulphide also gets oxidised into sulphur dioxide.
  • Atmospheric sulphur dioxide is carried back to the earth after being dissolved in rainwater as weak sulphuric acid (acid rain).
  • Whatever the source, sulphur in the form of sulphates is taken up by plants and incorporated through a series of metabolic processes into sulphur bearing amino acid which is incorporated in the proteins of autotroph tissues. It then passes through the grazing food chain.
  • Sulphur bound in a living organism is carried back to the soil, to the bottom of ponds and lakes and seas through excretion and decomposition of dead organic material .
Q. With reference to agricultural soils, consider the following statements:
  1. A high content of organic matter in soil drastically reduces its water holding capacity.
  2. Soil does not play any role in the Sulphur cycle.
  3. Irrigation over a period of time can contribute to the salinization of some agricultural lands.

Which of the statements given above is/are correct?

  1. 1 and 2 only
  2. 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
  • A high content of organic matter (humus) in soil increases its water holding capacity.

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Sir, one doubt u have given a list of about 500 national parks.do we have to cram whole of it.i am not finding it humanly possible.

No, you should only remember those that are in news recently.

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1.4.19.24: The Carbon Cycle - Biology

Carbon dating to determine the age of fossil remains

In this section we will explore the use of carbon dating to determine the age of fossil remains.

Carbon is a key element in biologically important molecules. During the lifetime of an organism, carbon is brought into the cell from the environment in the form of either carbon dioxide or carbon-based food molecules such as glucose then used to build biologically important molecules such as sugars, proteins, fats, and nucleic acids. These molecules are subsequently incorporated into the cells and tissues that make up living things. Therefore, organisms from a single-celled bacteria to the largest of the dinosaurs leave behind carbon-based remains.

Carbon dating is based upon the decay of 14 C, a radioactive isotope of carbon with a relatively long half-life (5700 years). While 12 C is the most abundant carbon isotope, there is a close to constant ratio of 12 C to 14 C in the environment, and hence in the molecules, cells, and tissues of living organisms. This constant ratio is maintained until the death of an organism, when 14 C stops being replenished. At this point, the overall amount of 14 C in the organism begins to decay exponentially. Therefore, by knowing the amount of 14 C in fossil remains, you can determine how long ago an organism died by examining the departure of the observed 12 C to 14 C ratio from the expected ratio for a living organism.

Decay of radioactive isotopes

Radioactive isotopes, such as 14 C, decay exponentially. The half-life of an isotope is defined as the amount of time it takes for there to be half the initial amount of the radioactive isotope present.

For example, suppose you have N0 grams of a radioactive isotope that has a half-life of t * years. Then we know that after one half-life (or t * years later), you will have

grams of that isotope.

t* years after that (i.e. 2t* years from the initial measurement), there will be

grams.

3t* years after the initial measurement there will be

grams,

and so on.

We can use our our general model for exponential decay to calculate the amount of carbon at any given time using the equation,

N (t) = N0e kt .

Modeling the decay of 14 C.

Returning to our example of carbon, knowing that the half-life of 14 C is 5700 years, we can use this to find the constant, k. That is when t = 5700, there is half the initial amount of 14 C. Of course the initial amount of 14 C is the amount of 14 C when t = 0 , or N0 (i.e. N(0) = N0e k&sdot0 = N0e 0 = N0). Thus, we can write:

.

Simplifying this expression by canceling the N0 on both sides of the equation gives,


.

Solving for the unknown, k , we take the natural logarithm of both sides,

.

Thus, our equation for modeling the decay of 14 C is given by,

.

Other radioactive isotopes are also used to date fossils.

The half-life for 14 C is approximately 5700 years, therefore the 14 C isotope is only useful for dating fossils up to about 50,000 years old. Fossils older than 50,000 years may have an undetectable amount of 14 C. For older fossils, an isotope with a longer half-life should be used. For example, the radioactive isotope potassium-40 decays to argon-40 with a half life of 1.3 billion years. Other isotopes commonly used for dating include uranium-238 (half-life of 4.5 billion years) and thorium-232 (half-life 14.1 billion years).

*****


Carbon Cycle and Ecosystems

Carbon is a fundamental part of the Earth system. It is one of the primary building blocks of all organic matter on Earth and a key element in setting Earth’s temperature. Carbon moves from the atmosphere to the land, ocean, and life through biological, chemical, geological and physical processes in a cycle called the carbon cycle. Because some carbon gases are greenhouse gases, changes in the carbon cycle that put more carbon in the atmosphere also warm Earth’s climate.

On the short time scale, the carbon cycle is most visible in life. Plants on land and in the ocean convert carbon dioxide to biomass (like leaves and stems) through photosynthesis. The carbon returns to the atmosphere when the plants decay, are eaten and digested by animals, or burn in fires. Because plants and animals are an integral part of the carbon cycle, the carbon cycle is closely connected to ecosystems. As ecosystems change under a changing climate, the carbon cycle will also change. For example, plants may bloom earlier in the year and grow for more months (assuming sufficient water is present) as the growing season gets longer, altering the food supply for animals in the ecosystem. If more plants grow, they will take more carbon out of the atmosphere and cool temperatures. If, on the other hand, warming slows plant growth, habitats will shift and more carbon will go into the atmosphere where it can cause additional warming.

Terra and the Carbon Cycle

Terra’s five instruments provide measurements of plant (vegetation) composition, structure, extent, and change. All four measurements are necessary to estimate how much carbon plants take up as they grow, and how much is being released to the atmosphere over time. Terra also measures concentrations of carbon monoxide in the atmosphere. Since Terra measurements begin in 2000, they provide a record of the rate and extent of change for more than a decade.

MODIS measures chlorophyll concentrations and fluorescence at the ocean surface to assess the concentration and health of photosynthesizing organisms like phytoplankton. Such measurements indicate how much carbon is taken up by ocean biology. MODIS also measures particulate organic carbon and particulate inorganic carbon, which can be used to gauge how much carbon the ocean exchanges with the atmosphere directly. See The Ocean’s Carbon Balance on the Earth Observatory.

Land vegetation

MISR collects data on the general height and structure of broad areas of vegetation (the canopy structure), the area covered by photosynthesizing leaves, and the amount of energy absorbed by leaves. Such measurements provide insight into carbon flux. MODIS collects a variety of measurements that indicate how much plants are growing, including vegetation indices, leaf area index, primary productivity, and evapotranspiration. See Measuring Vegetation on the Earth Observatory.

Land cover change

The MODIS land cover product indicates what type of vegetation is growing (forest, grassland, etc.) in a given location. Disturbance products, including the burned area product, show how land cover changes through deforestation or reforestation, agriculture, fire, urbanization, and so forth. ASTER’s 15 meter resolution imagery can be used to assess land cover change on a local scale, particularly as it relates to events like fires, floods, landslides, or volcanic eruptions. Although CERES does not directly collect data on carbon it does collect data on energy flux, in relation to energy balance, that takes place in vegetation and land surface.

MOPITT measures carbon monoxide in the atmosphere. While carbon monoxide (CO) is not itself a greenhouse gas, CO is chemically linked with methane, ozone, and carbon dioxide, and therefore impacts both climate and air quality. Primary sources of CO include fossil-fuel burning, biomass burning and methane oxidation. MOPITT measurements of CO concentrations in the troposphere are based on observations made with a suite of gas correlation radiometers operating in two CO-sensitive spectral bands. MOPITT CO products are used to study the movement of pollution in the atmosphere, to quantify CO emissions and to support air quality forecasts.


New study shows microbes trap massive amounts of carbon

Violent continental collisions and volcanic eruptions are not things normally associated with comfortable conditions for life. However, a new study, involving University of Tennessee, Knoxville, Associate Professor of Microbiology Karen Lloyd, unveils a large microbial ecosystem living deep within the earth that is fueled by chemicals produced during these tectonic cataclysms.

When oceanic and continental plates collide, one plate is pushed down, or subducted, into the mantle and the other plate is pushed up and studded with volcanoes. This is the main process by which chemical elements are moved between Earth's surface and interior and eventually recycled back to the surface.

"Subduction zones are fascinating environments--they produce volcanic mountains and serve as portals for carbon moving between the interior and exterior of Earth," said Maarten de Moor, associate professor at the National University of Costa Rica and coauthor of the study.

Normally this process is thought to occur outside the reach of life because of the extremely high pressures and temperatures involved. Although life almost certainly does not exist at the extreme conditions where Earth's mantle mixes with the crust to form lava, in recent decades scientists have learned that microbes extend far deeper into Earth's crust than previously thought.

This opens the possibility for discovering previously unknown types of biological interactions occurring with deep plate tectonic processes.

An interdisciplinary and international team of scientists has shown that a vast microbial ecosystem primarily eats the carbon, sulfur, and iron chemicals produced during the subduction of the oceanic plate beneath Costa Rica. The team obtained these results by sampling the deep subsurface microbial communities that are brought to the surface in natural hot springs, in work funded by the Deep Carbon Observatory and the Alfred P. Sloan Foundation.

The team found that this microbial ecosystem sequesters a large amount of carbon produced during subduction that would otherwise escape to the atmosphere. The process results in an estimated decrease of up to 22 percent in the amount of carbon being transported to the mantle.

"This work shows that carbon may be siphoned off to feed a large ecosystem that exists largely without input from the sun's energy. This means that biology might affect carbon fluxes in and out of the earth's mantle, which forces scientists to change how they think about the deep carbon cycle over geologic time scales," said Peter Barry, assistant scientist at the Woods Hole Oceanographic Institution and a coauthor of the study.

The team found that these microbes--called chemolithoautotrophs--sequester so much carbon because of their unique diet, which allows them to make energy without sunlight.

"Chemolithoautotrophs are microbes that use chemical energy to build their bodies. So they're like trees, but instead of using sunlight they use chemicals," said Lloyd, a co-corresponding author of the study. "These microbes use chemicals from the subduction zone to form the base of an ecosystem that is large and filled with diverse primary and secondary producers. It's like a vast forest, but underground."

This new study suggests that the known qualitative relationship between geology and biology may have significant quantitative implications for our understanding of how carbon has changed through deep time. "We already know of many ways in which biology has influenced the habitability of our planet, leading to the rise in atmospheric oxygen, for example," said Donato Giovannelli, a professor at the University of Naples Federico II and co-corresponding author of the study. "Now our ongoing work is revealing another exciting way in which life and our planet coevolved."

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Two sides of the same coin

Several recent articles by journalists and scientists have framed the plastic pollution problem as a distraction from the problem of climate change. The issue of plastic pollution may compete with climate change for funding and attention, delaying action what is a more pressing environmental issue, they say.

I disagree. Research shows that the plastic problem is not independent from climate change.

Greenhouse gas emissions from the burning of fossil fuels. (Pixabay)

Plastic and climate are two sides of the same coin: the majority of plastic polymers are made from petrochemical feed-stocks and their raw materials for synthesis are ethylene and propylene. These compounds are derived from naphtha, one of several chemicals refined from petroleum. What else is refined from petroleum? Gasoline, the fossil fuel we burn for energy that emits greenhouse gases.

These sister compounds are used differently but they have a common origin and they instigate the very issues in question. When demand for petroleum drops, companies ramp up their plastic production. When demand for plastic drops, fossil fuel companies might be inclined to shift their production ratio again. Failing to recognize the intimate connections between these issues not only makes tackling these issues inefficient, but may also undermine efforts on both fronts.


Carbon cycle

The carbon cycle is a complex cyclical process through which all of the carbon atoms in existence rotate. The same carbon atoms that exist in your body today have been used in many other molecules since time began - in a tree, in a plant and even in a dinosaur.

Step 1: Creation of fossil fuels

Under the right conditions carbon-based fossil fuels, coal, oil and gas are formed. These are mined from the ground.

Step 2: Fossil fuels releasing carbon

Carbon is released into the atmosphere when fossil fuels are burned.

Step 3: Decomposers

More carbon is released into the atmosphere by respiration of decomposers.

Step 4: Respiration

And finally carbon is released into the atmosphere by respiration of living organisms.

Step 5: Photosynthesis

Photosynthetic microbes and green plants take in carbon during photosynthesis and produce glucose (a sugar).

Step 6: Decomposition

Dead organisms and waste products decay bringing the carbon into the ground.

Overtime (millions of years) and under the right conditions some decomposed remains will be turned into fossil fuels such as coal and gas.

Algae as well as bacteria called cyanobacteria are similar to green plants because they can all make their own food through a process called photosynthesis.

Photosynthesis

Chlorophyll, the substance that makes algae and plants green, uses the energy from sunlight. In algae and plants it is contained in a structure called the chloroplast cyanobacteria carry out photosynthesis directly in the cytoplasm of the cell. The microbe uses this energy to change carbon dioxide gas from the air and the water around them into a sugar called glucose. The sugar is either transported to other cells and used as food or stored as insoluble starch. This process is called photosynthesis. The gas oxygen is released as a waste product. This is very important as animals including humans need oxygen to live. In fact 70 &ndash 80 % of all the oxygen we breathe comes from algae.

The chemical reaction for photosynthesis:

Carbon, which is represented by the letter C in the equation, is being transferred from the carbon in the carbon dioxide to the carbon in the glucose. This reaction forms part of the carbon cycle.

Aerobic respiration

Aerobic respiration takes place in the presence of oxygen and occurs in the opposite direction to the photosynthesis reaction. Aerobic respiration is the release of energy from glucose, which takes place inside the mitochondria of living cells.

The chemical reaction for aerobic respiration:

This reaction forms part of the carbon cycle.

Nitrogen cycle

Similar to the carbon cycle the nitrogen cycle is the process by which nitrogen in all its forms, cycles to the environment.

Food chain

All living things depend on each other to live. Find out where microbes are in the food chain.

Microbes and the human body

Ever wondered why when we are surrounded by microbes we are not ill all the time?

Microbes and food

Food for thought – bread, chocolate, yoghurt, blue cheese and tofu are all made using microbes.


Where is all our carbon?

  • Carbon is stored in all living things, the ocean, the atmosphere, soil and a lot of rock.
  • All carbon eventually passes through the atmosphere.
  • 99.9 per cent of carbon is stored in rock, mostly as limestone.
  • After rock, the ocean is the next biggest storage site with 38,000 billion tonnes of dissolved CO2.
  • Soil stores three times as much carbon as all the world's plants.
  • Plants and the ocean absorb slightly more CO2 than they release each year, making up for half the excess carbon we release.

Individual atoms of carbon constantly move from one form to another - in air, water, living things and rock. The movement is managed by different chemical and physical processes, from photosynthesis, respiration, combustion and plate tectonics, to plain old dissolving and off-gassing.

And the one thing that all of these carbon paths have in common is that they all pass through the atmosphere, because they all at some stage turn carbon into a gas, and gases float.

Together those paths that carbon can take make up a cycle. But unlike the simple water cycle (evaporation - clouds - rain - evaporation), the carbon cycle takes place in all parts of the planet and across all time scales.

In fact, the cycle takes place in such different time scales - from a fraction of a second to many millions of years - that there are really two carbon cycles, the quick and the slow.


Contents

The two main cycles are the land-atmosphere cycle, and the ocean-atmosphere cycle. They both occur on very different timescales, with the land cycle occurring at a high rate while the ocean cycle is much slower.

  • Land-atmosphere - this cycle occurs via two main drivers photosynthesis and respiration. In photosynthesis, carbon dioxide is absorbed from the atmosphere to create a fuel for the plant, while respiration consumes oxygen and produces carbon dioxide. Respiration also occurs via decaying matter, in which the compounds making up the matter decompose by bacteria which consumes oxygen along with the matter to produce energy and carbon dioxide. ΐ]
  • Ocean-atmosphere - the driving mechanism for this cycle is the difference in carbon dioxide's partial pressure between the ocean and atmosphere (partial pressure is the pressure the gas would have if it occupied the entire volume of the mixed solutions, in this case the volume of the ocean and atmosphere). This pressure varies with both the temperature of the ocean, and the local marine photosynthesis. The lower the ocean temperature is the less carbon is emitted (much like how a warm glass of pop becomes flat more quickly). Therefore some regions of the ocean take in carbon (carbon sink) while some emit carbon (carbon source). ΐ]

35 gigatonnes of carbon dioxide) becomes an extra 4 gigatonnes in the atmosphere, an extra 3 gigatonnes of photosynthesis and an extra 2 gigatonnes in the ocean every year. This is how humans are changing the natural carbon cycle.


Follow the Carbon

Understanding the carbon cycle is fundamental to making sense of environmental changes such as global warming and ocean acidification. This model shows the relative abundance of carbon in each of the earth’s main carbon reservoirs, and also shows the yearly exchanges between these reservoirs.

Tools and Materials

  • Five pounds rice (or other small grain or material)
  • Cups or other containers for counting and weighing rice
  • Scale
  • Permanent marker
  • Four gallon-sized plastic zip-top bags
  • Five quart or sandwich-sized plastic bags
  • A box with the dimensions 10 cm x 10 cm x 10 cm (this can be made from a 1/2 gallon paperboard milk carton, cut in half)
  • Meter stick
  • Carbon reservoir images

Assembly

Note: A gigaton of carbon (GtC) and a petagram of carbon (PgC) are the fundamental units of measurement of carbon at planetary cycling scales. One gigaton is equal to one billion metric tons of carbon (or one petagram, which is 10 15 grams). They are interchangeable, and we will use GtC in this Snack.

  1. Before you begin, ask participants if they can think of any of the earth’s carbon reservoirs. The five major carbon reservoirs are: Rock, Atmosphere, Oceans, Terrestrial Biosphere, and Fossil Fuels.
  2. Each participant should count 100 grains of rice, and combine 5 of these to make 500 grains total. Find the mass of this amount. (In our sample, 500 grains of rice had a mass of 15 grams.) To create an accurate model of the relative abundance of carbon present in each of the five major carbon reservoirs, let each grain of rice represent 1 gigaton of carbon (GtC). If you have a large group, you will be able to use all those "extra" 100s of grains of rice for the next step.
  3. Using the chart below (click to enlarge), calculate how many grams of rice represents the amount of carbon in each of the four reservoirs (listed in bold) except Rock.
  4. Use a marker to label four of the gallon-sized bags with the name of each of the four major reservoirs except Rock. (Because rock contains a large amount of carbon, it cannot be physically represented by this model, so no bag will be needed for it.) Then, using the scale, measure the amount of rice that corresponds to the amount of carbon in each reservoir and place it into the correct bags. You may want to divide participants into four groups—one for each carbon reservoir—to do this step most efficiently.
  5. If something is too large to be represented by a physical model, it can help to find a way to visualize it. To help imagine the amount of rice needed to represent the carbon in the Rock reservoir, determine how many grains will fit inside the 10 cm x 10 cm x 10 cm box. How many of those rice-filled boxes would you need to represent the amount of carbon in the Rock reservoir? How much space in the room would all those boxes take up? (A meter stick might be helpful to make these calculations.)
  6. Place the appropriate carbon reservoir image with the bag of rice that represents that reservoir.

To Do and Notice

These investigations will help you model how carbon flows from one reservoir to another.

Note: Before you begin, notice the relative abundance of carbon in each of the five reservoirs. Rock contains far more carbon than the other four reservoirs combined. Since rock is part of the slow carbon cycle, it is not part of the exchanges you will model in this snack.

Pathway 1: Flow between the Atmosphere and Terrestrial Biosphere

The natural flux between the atmosphere and terrestrial biosphere is about 120 GtC per year in each direction. In the terrestrial biosphere, photosynthesis removes about 120 GtC from the atmosphere each year. Decomposition of biological material and respiration from plants and soil microbes returns 120 GtC to the atmosphere each year.

To model this interaction, remove 120 grains of rice from the Atmosphere bag and place it in a quart-sized bag. Then do the same with the Terrestrial Biosphere bag. Exchange these two equal-sized bags while discussing how the carbon flows from one reservoir to another. Model this yearly exchange several times while reviewing the ways in which carbon cycles from one reservoir to the other.

Pathway 2: Flow between the Ocean and the Atmosphere

Carbon cycles between the ocean and the atmosphere at a rate of 90 GtC per year in each direction. Most of this exchange occurs by diffusion at the surface of the ocean.

To model this interaction, remove 90 grains of rice from the Atmosphere bag and place it in a new quart-sized bag. Then do the same with the Ocean bag. Exchange these two equal-sized bags while discussing how the carbon flows from one reservoir to another. Model this yearly exchange several times, while reviewing the ways in which carbon cycles from one reservoir to the other.

Notice that, until now, the carbon cycle has remained in balance, and no reservoir has a net gain or loss.

Pathway 3: Flow from Fossil Fuels

Human use of fossil fuels (the burning of which releases carbon dioxide into the atmosphere) is changing the balance of carbon, adding an additional 9.4 (±0.5) GtC to the atmosphere each year. Land use changes, such as deforestation, remove part of the carbon sink (materials in the natural environment capable of absorbing excess carbon), thereby “contributing” that addition of 1.5 (±0.7) GtC excess carbon. Human impacts are therefore contributing almost 11 GtC per year to the atmosphere.

To model this interaction, count 11 grains of rice from the Fossil Fuels bag.

Not all of this carbon goes into the Atmosphere, as other reservoirs are absorbing some of this added carbon. Each year 4 GtC (represented by 4 grains of rice) from the Fossil Fuels reservoir are absorbed by the Terrestrial Biosphere, and 3 GtC (3 grains of rice) are absorbed by the Ocean reservoir. This results in a net gain in the Atmosphere reservoir of 5 GtC (5 grains of rice) per year with a budget imbalance of 0.5 GtC per year indicating overestimated emmisions and/or underestimated sinks (see the equation below).

What’s Going On?

This activity models the fast carbon cycle, which involves the carbon reservoirs of the ocean, atmosphere, and biosphere. The fast carbon cycle takes place over months to years. The slow carbon cycle, which is the geochemical part of the carbon cycle, involves the cycling of carbon-containing rocks, takes thousands to millions of years, and is not modeled in this exercise.

The carbon cycling between the ocean, atmosphere, and biosphere was in balance until the Industrial Revolution, when fossil fuels were brought out of the rock (where they were part of the slow carbon cycle) and burned for energy, releasing a huge amount carbon (in the form of CO2) into the atmosphere, and into the fast carbon cycle. As a result, the carbon cycle is no longer in balance.

Today, carbon from fossil fuels, normally part of the slow carbon cycle, is being added to the atmosphere, and the fast carbon cycle cannot absorb it at the same rate. This has increased the amount of carbon in the atmosphere by about 5 GtC per year (2018). While natural processes can use up this additional carbon, these processes are part of the slow carbon cycle, and take hundreds of thousands to millions of years.

The consequences of the additional atmospheric carbon are many, and include increased atmospheric and oceanic temperatures, sea level rise, and ocean acidification.

Each year, the oceans absorb and release about 90 GtC, largely via diffusion across the air-ocean interface. The physical processes that control the sinking of CO2 into colder, deeper waters (where CO2 is more soluble), and the mixing of ocean water at intermediate depths, are known collectively as the “solubility pump,” and are not part of this model. Phytoplankton photosynthesis converts CO2 into organic carbon that is largely returned to ocean water as CO2 via microbial respiration and decomposition. The small fraction of organic carbon that is encapsulated by certain plankton into degradation-resistant clumps that sink to the ocean floor is called the “biological pump.” Together, the solubility pump and biological pump control the amount of carbon transported to ocean depths and the exchange of CO2 between ocean and atmosphere.

Going Further

The carbon amounts used in this model are based on solid carbon, which is not the form that carbon takes in all of the earth’s carbon reservoirs. As you can see from this list, carbon can take many different forms.

Rock: 65,300,000 GtC

The carbon in rock is mostly solid carbonate, such as limestone (calcium carbonate, CaCO3). Rocks are by far the largest reservoir of carbon on earth, but changes in the flow of carbon to and from this reservoir are extremely slow, and have no real impact on changes to the global carbon cycle at human timescales (tens to thousands of years). The carbon rock cycle is part of the slow carbon cycle, which takes hundreds of thousands to millions of years.

Atmosphere: 879 GtC (in 2018)

In the atmosphere, carbon is in a gaseous form. The most abundant carbon-containing gas is carbon dioxide (CO2) others are methane (CH4), and carbon monoxide (CO).

Ocean: 40,453 GtC

At the surface of the ocean, carbon shows up as dissolved carbon dioxide (CO2), carbonic acid (H2CO3), bicarbonate ions (HCO3 - ), and carbonate ions (CO3 -2 ). The relative abundance of these carbon compounds is controlled by the pH of the water. CO2 dissolves in seawater, creating carbonic acid, which releases H+ ions. H+ ions combine with carbonate in seawater to form bicarbonate, which doesn’t easily escape the ocean.

Terrestrial Biosphere: 1,950 GtC

The carbon in the biosphere—mostly organic plant material and soils—takes the form of simple sugars like glucose or fructose, and more complex molecules like starch and cellulose.

Fossil Fuels: 1,000 GtC

The carbon in fossil fuels includes solid coal, liquid hydrocarbon petroleum, and gas hydrocarbon methane, which resulted from photosynthesis hundreds of millions of years ago and subsequent burial. Because fossil fuels are sequestered in rock, they are also part of the slow carbon cycle.

Resources

The amount of carbon moving between reservoirs is changing every year. The data use in this Snack were based on annual fluxes from 2005–2014. Here are some of the sources we used:

Le Quéré, Corinne et al. "Global carbon budget 2018." Earth System Science Data, 10, 2041 - 2194, 2018.


Watch the video: The Carbon Cycle Process (July 2022).


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