Chapter 55

Carbon CyclingEssential Idea: Continued availability of carbon

in ecosystems depends on carbon cycling.

Model for Nutrient CyclingModel for Nutrient Cycling

As stated in the last section, when we look at nutrient cycling, we have to consider:

• The main reservoirs for elements.• Processes that transfer the elements

between reservoirs.

Model for Nutrient CyclingModel for Nutrient Cycling

Each reservoir has two questions that need to be answered: Does it contain organic

or inorganic materials? Are the materials directly

available for use by organisms?

Carbon CycleCarbon Cycle Carbon is important because it forms the

framework for organic molecules essential to all life.

http://www.algen.si/node/83

Carbon CycleCarbon Cycle Photosynthesis makes use of CO2 by

converting it into forms used by consumers.

http://www.algen.si/node/83

Carbon CycleCarbon Cycle Carbon is found in great proportions in

fossil fuels, sediments of aquatic ecosystems, the oceans, plants and animal biomass, and the atmosphere.

Reservoir Carbon (gigatons)

Percent of Total Carbon

on EarthOceans 38 x 103 0.05

Rocks and Sediments 75 x 106 >99.5

Terrestrial Biosphere 2 x 103 0.003

Aquatic Biosphere 1-2 0.000002

Methane Hydrates 1 x 104 0.006

Fossil Fuels 4.2 x 103 0.014http://www.algen.si/node/83

Carbon CycleCarbon Cycle Additionally, aquatic ecosystems contain

carbon as dissolved CO2 and hydrogen carbonate ions.

Carbon CycleCarbon Cycle The largest carbon reservoir is found in

sedimentary rocks like limestone.

Bob Krist/Corbis

Limestone

Limestone

Limestone• Animals such as

reef-building corals and mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.

Carbon CycleCarbon Cycle Key processes concerning the carbon

cycle are: The conversion of CO2 into

carbohydrates and other carbon compounds by autotrophs. CO2 + H2O --> C6H12O6 + O2

The return of CO2 to the atmosphere through cell respiration. C6H12O6 + O2 --> CO2 + H2O

Carbon CycleCarbon Cycle When CO2 is produced by heterotrophs, it

diffuses out of the organism and into the water or the atmosphere.

Carbon CycleCarbon Cycle The CO2 in the atmosphere then diffuses

into autotrophs in the atmosphere or water.

travismulthaupt.com

Carbon CycleCarbon Cycle As stated in the last

section, volcanoes contribute a lot of CO2 to the atmosphere over geologic time.

The burning of fossil fuels is also adding a lot of CO2 to the atmosphere.

Methane• Methane is produced from organic matter

in anaerobic conditions by methanogenic archaeans.• It is done so in the absence of O2.• Anthropogenic sources• Natural sources.

www.biogas-renewable-energy.info

Methane• Some diffuses

into the surrounding water, bubbles into the atmosphere, or is trapped and accumulates in the ground.

https://www1.ethz.ch/ibp/research/environmentalmicrobiology/research/Wetlands

Methane• Natural sources of methane

include swamp bottoms, ruminant animals, wets soils where organic decay is occurring in anaerobic conditions.

• Anthropogenic sources include rice paddies, land fills, sewage treatment plants, etc.

http://www.climate-change-knowledge.org/ghg_sources.html

• Methane is a potent greenhouse gas and needs to be limited as much as possible to stem global warming/climate change.

Methane

www3.edp.gov

Methane• Methane removal from the atmosphere

comes from the chemical reaction of methane with a hydroxyl radical producing water and carbon dioxide.

• Methane removal in the soil comes from the action of methanotrophs.

Methane• Certain microorganisms in the soil are

able to use single-carbon compounds such as methane as a fuel.

• Using a complex pathway, they break methane down into CO2 and water.

https://microbewiki.kenyon.edu/index.php/Methylothermus_thermalis

Peat Formation

• Peat forms when plant material is inhibited from fully decaying by acidic and anaerobic conditions.

• It is composed mostly of wetland vegetation: principally mosses, sedges and shrubs.

Peat Formation

• When the soil becomes waterlogged, it often becomes anaerobic, acidic, or both and this contributes to the formation of peat.

Peat Formation

• Peat formation is the first step in the formation of coal.

• The formation of coal takes millions of years.

http://www.infoplease.com/dk/encyclopedia/energy-resources.html

Peat Formation

http://blogs.ubc.ca/thearodgers/2015/05/03/impacts-of-climate-change-on-carbon-emissions-from-canadian-peatlands/

Peat Formation

• Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulated in porous rocks.

serc.carleton.edu

Oil Formation

• Millions of years ago, plants and animals living in the ocean absorbed energy from the sun and stored this energy in their bodies in the form of carbon. 

Oil Formation• As these animals died, their bodies

sank to the bottom of the ocean where they were covered with layers of sediment deposits.

www.artinaid.com

• As these layers of sediment increased the heat and pressure exerted on these remains began to rise. 

Oil Formation

www.geocaching.com

• The degree of heat and the amount of pressure, along with the type of biomass, directly influenced whether oil or natural gas was formed. 

• As heat increases, a lighter gas is formed. 

• If the temperature raises to an even higher heat, or if the biomass is predominantly plant material, natural gas is formed. 

Oil Formation

www.need-media.smugmug.com

• As heat increases, a lighter gas is formed.  If the temperature raises to an even higher heat, or if the biomass is predominantly plant material, natural gas is formed. 

Oil Formation

www.need-media.smugmug.com

• After oil is formed, it travels from the source rocks, where it was formed, through tiny pores in the surrounding rock until it either seeps through the rock onto the surface or is trapped beneath a layer of impermeable rock or clay and forms a reservoir. 

Oil Formation

• Reservoirs range in depth below the surface.  Some are only hundreds of feet below, while others have been discovered at depths greater than 30,000 feet.  Still others are discovered offshore, and are covered with thousands of feet of water on top of tens of thousands of feet of sediment. 

Oil Formation

• The majority of reservoirs are made up of oil, gas, and water.  These fluids are generally separated into layers due to the influence of gravity and differences in density.  Gas, being the less dense of the three, migrates to the top, followed by oil and then water.  

Oil Formation

• 70% of oil deposits were formed in the Mesozoic age, 20% were formed in the Cenozoic age, and 10% were formed in the Paleozoic age.  These differences are the result of many factors,  The Mesozoic climate was primarily tropical worldwide, plankton were very abundant in the ocean, the ocean bottoms stagnant and anoxic (preventing the occurrence of decomposition), and organic-rich muds accumulated and formed later source rocks.

Oil Formation

Burning of Fossil Fuels

• When these fossil fuels are burned, CO2 is produced reentering the carbon cycle.

• Currently, we are producing far more CO2 than can be taken out of the atmosphere.

Oil Formation

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