Phenomenon
Since 1958, researchers have been measuring the amount of CO2 in the atmosphere at Mauna Loa Observatory in Hawaii. The center line shows yearly averaged CO2 and the oscillating line shows seasonal fluctuations in CO2 levels.
Focus Questions: Give your best response prior to learning about this topic. Your initial answers may change as you explore this unit.
Bio.1.3 Carbon Cycle
The Carbon Cycle
How does carbon move through different ecosystems and what are some of those effects?
Flowing water can slowly dissolve carbon in sedimentary rock. Most of this carbon ends up in the ocean. The deep ocean can store carbon for thousands of years or more. Sedimentary rock and the ocean are major reservoirs of stored carbon. Carbon is also stored for varying lengths of time in the atmosphere, in living organisms, and as fossil fuel deposits. These are all parts of the carbon cycle, which is shown in the next figure.
The Carbon Cycle. Carbon moves from one reservoir to another in the carbon cycle. What role
do organisms play in this cycle?
Why is recycling carbon important? Carbon is the cornerstone of organic compounds, the compounds necessary for life. But do organisms make their own carbon? Do they have the genes that encode proteins necessary to make carbon? No. In fact, there are no such genes. Carbon must be recycled from other living organisms, from carbon in the atmosphere, and from carbon in other parts of the biosphere.
Photosynthesis and cellular respiration recycle carbon. Autotrophs take carbon from the atmosphere and convert it to organic molecules. Protein, carbohydrates, and fats are all parts of heterotrophs and all contain carbon. When organisms break down food to produce energy, they break down protein, carbohydrates, and fat, and release carbon dioxide.
Carbon in the Atmosphere
Though carbon can be found in ocean water, rocks and sediment and other parts of the biosphere, the atmosphere may be the most recognizable reservoir of carbon. Carbon occurs in various forms in different parts of the carbon cycle. Some of the different forms in which carbon appears are described in the Table below.
Carbon in Carbon Dioxide
Carbon cycles quickly between organisms and the atmosphere via photosynthesis and respiration. In the atmosphere, carbon exists primarily as carbon dioxide (CO2). Carbon dioxide cycles through the atmosphere by several different processes, including those listed below.
Because of human activities, there is more carbon dioxide in the atmosphere today than in the past hundreds of thousands of years. Burning fossil fuel has released great quantities of carbon dioxide into the atmosphere. Cutting forests and clearing land has also increased carbon dioxide into the atmosphere because these activities reduce the number of autotrophic organisms that use up carbon dioxide in photosynthesis. In addition, clearing often involves burning, which releases carbon dioxide that was previously stored in autotrophs. Carbon cycles through the atmosphere relatively quickly.
Human Actions Impact the Carbon Cycle
Humans have changed the natural balance of the carbon cycle because we use coal, oil, and natural gas to supply our energy demands. Fossil fuels are a sink for CO2 when they form, but they are a source for CO2 when they are burned.
The equation for combustion of propane, which is a simple hydrocarbon looks like this:
The equation shows that when propane burns, it uses oxygen and produces carbon dioxide and water. So when a car burns a tank of gas, the amount of CO2 in the atmosphere increases just a little. Added over millions of tanks of gas and coal burned for electricity in power plants and all of the other sources of CO2, the result is the increase in atmospheric CO2 seen in the Figure above.
The second largest source of atmospheric CO2 is deforestation (Figure below). Trees naturally absorb CO2 while they are alive. Trees that are cut down lose
their ability to absorb CO2. If the tree is burned or decomposes, it becomes a source of CO2. A forest can go from being a carbon sink to being a carbon source.
This forest in Mexico has been cut down and burned to clear forested land for agriculture.
Effects of Carbon in the Oceans on Ecosystems
As the oceans absorb CO2, the minerals in the seawater change. Normally, the ocean has a lot of calcium carbonate available. Shellfish and coral use this mineral to build and repair their shells. When an area of the ocean experiences an increase in carbon dioxide, a chemical reaction makes the calcium carbonate unavailable This causes shells to thin, coral to stop growing and animals die. Many sea animals spend at least part of their life cycles on the reefs. As these ecosystems disappear, species will die out, the food web will experience disruptions, and our oceans will become less diverse.
Many oceanographers say that this threat to the ecosystem is actually more urgent than the threat posed by global warming. Coral reefs take thousands of years to grow, but can deteriorate in only a few decades. Without some sort of a change, we may be looking at a future where the seas are a little more acidic, and a lot less lively.
Putting It Together
Focus Questions
Final Project
Explore products being developed to reduce or clean up human carbon emissions. Pick one of these products and create a full-color advertisement for it.
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