Carbon Cycling Internal

Transcription

1 Carbon Cycling Internal The 4 subcycles Atmosphere The Earth s Atmosphere The Earth has a radius of some 6400 km. Ninety-nine percent of the earth's atmosphere is contained within a layer approximately 50 km thick. Life on earth inhabits a layer about 9 km thick, extending from a few kilometres above sea level to a few kilometres below. The atmosphere is a mixture of gases. Nitrogen and oxygen make up 99% of air. 1% are "trace" gases, especially argon. Two other trace gases, carbon dioxide and ozone, have a large impact on humans and all other life. Water vapor is also present in small amounts. It absorbs heat from the Earth and Sun.

2 The atmosphere is divided into four layers based on temperature: the troposphere, stratosphere, mesosphere, and thermosphere. We live in the troposphere.90% of our air is in this layer. This is where all our weather occurs. Gravity keeps the atmosphere denser close to the earth's surface

3 How it Works: Greenhouse gases act like an invisible blanket that traps just enough energy, in a similar way that glass traps heat inside a greenhouse. Without them the Earth's average surface temperature would be a cold, 18 C rather than the pleasant 15 C. The most important greenhouse gas is carbon dioxide. Carbon dioxide has a huge effect on climate. Sunlight warms the Earth s surface which then radiates out heat into the atmosphere. Carbon dioxide molecules absorb some of this heat, insulating the surface of the Earth from the cold of space and warming the land and ocean. When we talk about the greenhouse effect we mean the ENHANCED effect which is caused by the increase of greenhouse gases from human sources. Causes The main sources of these emissions, particularly carbon dioxide, methane and nitrous oxide, are: the combustion of large amounts of fossil fuels (producing CO2)

4 deforestation (less trees mean that less CO2 is being mopped up) often to provide land for farming. decay (producing CO2 if oxygen is present, methane (CH4) if it is not.) Not all of the Carbon Ends up in the Air Curiously, the increase in atmospheric CO2 is only about one-half of what would have been expected from the amount of fossil fuel consumption and forest burning. Where has the rest gone? Research has shown that increased CO2 levels lead to increased net production by photoautotrophs. There is evidence that at least some of the missing CO2 has been incorporated by increased growth of forests, especially in North America; increased amounts of photoautotrophic plankton in the oceans; uptake by desert soils (mechanism as yet unknown). Resources DVD BBC Earth- the power of the planet BBC How the Earth made us Oceans The role of the oceans The oceans have two important roles in helping keep a stable climate on Earth. 1. The great ocean currents play a very important part in maintaining a steady climate. They transport huge quantities of heat in enormous volumes of water. The thermohaline current is a current that travels around the whole world, mixing water from all the oceans and distributing heat. This current has a huge influence on our climate. Part of the current flows on the surface of the ocean and part flows far under the surface in deep ocean basins. Cold dense water forms in the Arctic Sea and around Antarctica and sinks. Warm less dense water from other parts of the ocean moves to replace the sinking cold dense water.

5 This is what causes circulation forming the global thermohaline current which spreads heat around the whole world. 2. Ocean circulation also influences the amount of carbon dioxide in the atmosphere in 2 ways: Waves on the surface of the ocean cause CO2 from the atmosphere to be dissolved into the water. The colder the water, the more carbon dioxide can be absorbed. Tiny marine plants called phytoplankton, lock up carbon dioxide as part of their bodies in the form of calcium carbonate shells. When they die they sink to the bottom of the ocean and become part of the deep sea sediments. Carbon dioxide is removed this way for several million years.

6 Photos of plankton that have shells made of calcium carbonate. When these shells fall to the ocean bottom they become part of the sediment accumulating there. The sediment gets compacted and limestone, which is calcium carbonate, is formed.

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8 Exercise Waves on the surface of the ocean cause from the atmosphere to be dissolved into the water. The colder the water, the more can be absorbed. Tiny marine plants called lock up carbon dioxide as part of their in the form of shells. When they die they to the bottom of the ocean and become part of the deep sea. Carbon dioxide is removed this way for years. In your own words write (in your book) about how carbon is cycled in the oceans. Use these key words as part of your answer: carbon dioxide, dissolved, carbonates,

9 photosynthesis, respiration, phytoplankton, sedimentation, weathering, uplift (remember that phytoplankton is the sea s producer and carbon enters food chains in the ocean through phytoplankton). Biocycle Plants & The Carbon Cycle Plants take in carbon dioxide and convert it to sugar which can be stored until used for energy. This process is called photosynthesis. 6CO 2 + 6H 2 O sunlight 6O 2 + C 6 H 12 O 6

10 Plants release carbon dioxide as a waste product when they convert their stored sugar to chemical energy. This process is called respiration. Animals & The Carbon Cycle Animals eat carbon contained in animal and plant tissues and release carbon dioxide as a waste product. This process is respiration. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Aerobic vs Anaerobic Respiration Aerobic respiration is the process that takes place in presence of oxygen (see above slide). Aerobic respiration is a high energy yielding process. Anaerobic respiration is the process of oxidation of molecules in the absence of oxygen. Anaerobic respiration can occur in any of the following ways : Glucose Energy + Ethanol + Carbon dioxide (CO 2 ) Glucose Energy + Lactic acid Glucose methane and water + energy

11 Decay & The Carbon Cycle Decomposers release the carbon from dead plant and animal tissues back into the atmosphere. Decomposers, when they break down dead organic matter, release carbon dioxide into the air also. Decomposers are essential because without them, all of the carbon on the planet would eventually become locked up in dead carcasses. Storage In the bio cycle carbon is stored in leaves of plants. A percentage passes to herbivores which store it in their tissues as muscle, fat and glycogen. A percentage of this is then passed onto carnivores. Decomposers return this carbon to the soil and air in the short term. Long term storage can occur when the carbon stored in the lignin of plants is buried and fossilised into coal. Over millions of years fossil fuels may form from the buried remains of plants and animals.

12 Agriculture Agriculture affects the carbon cycle in the following ways: 1. Organic matter (mostly carbon) affects soil quality. 2. Crop residues create organic matter. 3. Manure adds organic matter. Intensive tillage, burning fuels and the use of equipment adds CO 2 to the atmosphere.

13 No-till systems remove CO 2. Why no-till systems are good 1. Organic matter stays put. 2. Earthworms thrive. 3. Root channels remain undisturbed. 4. Prevents soil from crusting. 5. Water holding capacity improves. 6. Nutrient exchange improved. 7. Crop residues stay on surface. 8. Soil compaction reduced. 9. Long term crop production improved.

14 Geocycle/Lithocycle Tectonic plates and volcanoes Earth is the only planet in our Solar System with tectonic plates. Although plate tectonics involves the solid parts of the planet it still has an important part to play in keeping the climate steady. The crust and the hard upper part of the mantle are broken into giant rock plates called tectonic plates which float on the softer, lower mantle. The core of Earth gives off an enormous amount of heat which keeps the rock in the lower part of the mantle soft and able to be moved along by giant convection currents. This moves the tectonic plates so that sometimes they collide and other times move apart from each other. When plankton with shells made of calcium carbonate die the shells fall to the ocean bottom and become part of the sediment accumulating there. The sediment gets compacted and forms rock. Rock formed from compressed plankton shells is called limestone. Both the shells and limestone is made of calcium carbonate. This sediment will remain on the bottom of the ocean forming deeper and deeper layers of limestone. Eventually much of the limestone will become subducted when two tectonic plates collide, as is happening off the coast of the North Island. The limestone is subducted deep into the ground where it may be melted and become magma. Most of the volcanoes around the world occur along boundaries between tectonic plates. When magma is erupted from a volcano vast amounts of carbon dioxide are released back into the atmosphere.

15 1. Carbon dioxide (and other greenhouse gases) keeps the Earth at a pleasant, average temperature of about 15 degrees. 2. This warmth means that seawater evaporates, forming clouds and rain. 3. Rain contains dissolved carbon dioxide (CO 2 ) from the atmosphere which makes it slightly acid. Therefore it dissolves minerals from rocks which go into water such as rivers and lakes. 4. The water and minerals are washed out to sea. The minerals settle on the ocean floor or are made into the shells of tiny plankton. 5. When plankton die their shells settle onto the ocean floor where they become part of seafloor sediment. This sediment forms thick layers which become compacted to form limestone. 6. When two tectonic plates collide one plate is often subducted under the other. When this happens the limestone will be subducted too.

16 7. When the subducted plate reaches a certain depth, the limestone, along with other rock and sediment, will melt forming magma. 8. Molten magma rises and is erupted from volcanoes as lava, ash and gases, including vast amounts of carbon dioxide. The carbon dioxide enters the atmosphere.

17 This cycle is an extremely effective thermostat. When the planet is warm, more water evaporates from the oceans and rainfall increases. Because carbon dioxide is easily dissolved in water, the extra rain speeds up the rate of atmospheric carbon dioxide removal. This means that there is less greenhouse gas in the atmosphere and therefore less heat can be trapped. The planet is cooled. When it is cold, less water evaporates from the oceans, rainfall decreases, allowing volcanic gases to build up in the atmosphere, warming the planet.