Carbon Oxygen Cycle

CFC destruction of ozone

(1) UV + CF2Cl2 → CF2Cl + Cl (2) O3 + Cl → O2 + ClO (100 000 O3: 1 Cl) (3) ClO + O → O2 + Cl (4) ClO + OH → HCl (acid rain) + O2

Solar formation of ozone

(1) UV + O2 → O + O + heat (2) O2 + O → O3

Solar destruction of ozone

(3) UV + O3 → O2 + O + heat

4 main reservoirs through which carbon moves

- Atmosphere - Terrestrial organisms, referred to as biota - Ocean - Land

Inorganic Forms and Location of Carbon and Oxygen (Abiotic)

- CO2 gas in the atmosphere - CO2 dissolved in water as HCO3 and CO3 ̄ "sink effect" - CO2 in the skeletons and shells or aquatic organisms (including planktons) as CaCO3 (biosynthesis) - CO2 in sedimentary rock (limestone) as CaCO3 (uplift & weathering) - O2 in the troposphere and soil air spaces - O2 dissolved in water - O2 and O3 (ozone) in the stratosphere absorb ultraviolet radiation

Organic Forms and Location of Carbon (Producers and Consumers)

- Carbohydrates and other organic molecules in Plants (Producers) - Eating - Carbohydrates and other organic molecules in Animals (Consumers) - Fossil fuel formation - Fossil fuels: Oil Gas Coal

Organic to Inorganic Conversion Processes (Consumers and Decomposers)

- Cellular respiration - Decomposition - Combustion

The Greenhouse Effect and Global Warming

Carbon dioxide is transparent to light but rather opaque to (absorbs) heat rays. - Therefore, CO2 in the atmosphere retards and absorbs/traps the radiation of heat from the earth back into space—the "greenhouse effect".

Carbon Cycle

All living things are composed of organic molecules, which are carbon-based compounds. - Therefore, the carbon cycle is extremely important. - The exchange pool for carbon is the atmosphere where the carbon resides in the form of carbon dioxide. - Carbon enters the biotic community through the process of photosynthesis in which CO2 is removed from the air and used to make carbohydrates. - Carbon moves through trophic levels, and at every level cellular respiration releases CO2 into the atmosphere. - The burning of fossil fuels has significantly increased the amount of CO2 in the atmosphere.

Carbon Cycle Analogy

Although we don't usually think of carbon in our day to day lives, carbon plays the central role in the "reduction-oxidation battlefield" that we call life. - On the one side of the battlefield you have the photosynthetic organisms that use light energy and atmospheric CO2 to produce a pool of reduced organic compounds with high potential energy, plus a reservoir of oxygen. - On the other side of the battlefield you have the heterotrophic creatures, like ourselves, that are trying to release this stored energy by oxidizing the reduced organic compounds, consuming O2 and adding CO2 to the atmosphere in the process.

Biogeochemical Cycles

Besides energy, all organisms require various nutrients. - In addition to water molecules, the elements of primary importance in these nutrients are carbon, nitrogen, oxygen and phosphorus. - Nutrients, unlike energy, are recycled through ecosystems in nutrient (biogeochemical) cycles. For each element, the cycle may involve: 1) a reservoir, in which the nutrient is present but temporarily unavailable, 2) an exchange pool, which is the primary source of nutrients, (atmosphere, lithosphere soil, hydrosphere) and 3) the biotic community, which consists of the organisms through which nutrients pass. Human activities have altered nutrient cycles.

Volcanic Activity

CO2 concentrations in the atmosphere are related to volcanic activity. - The concentration of CO2 has varied over a large range in our atmosphere in the geologic past. - When volcanic activity is high, the CO2 concentration in the atmosphere is also high due to the release of CO2 from volcanoes into the atmosphere. - Particles released by large, single volcanic eruptions today can cause a slight (but temporary) cooling of the Earth's surface.

Rock Weathering

Carbon in the rocks is consumed in the weathering of many rocks. This weathering produces bicarbonate (HCO3-), a form of inorganic carbon, and calcium (Ca2+) that are then transported in riverwater to the oceans. - Once in the oceans, the calcium and bicarbonate are combined by organisms (biosynthesis) to form calcium carbonate, the mineral that is found in shells and skeletons of microscopic diatom phytoplankton. - This calcium carbonate mineral is buried in the sediments. - High-temperature processes convert some of the calcium carbonate back to CO2, which is released to the atmosphere to begin the cycle over again.

Human Activity

Humans are changing the CO2 cycle by burning fossil fuels and biomass (e.g., forests). - These increases in CO2 are linked to increased warming in our atmosphere. - Since humans started to pump CO2 into the atmosphere there has been a large increase in atmospheric CO2, and this increase will undoubtedly continue in the future. - An important point to consider is that even if we stopped our emissions of CO2 today, we would still experience climate change because of what has already been set in motion. - The burning of fossil fuels releases carbon dioxide from carbon stores long-buried in the earth. - This adds excess to the levels of carbon dioxide in the atmosphere, increasing the greenhouse effect and contributing to global warming.

Oceans

Oceans play a major role in determining carbon dioxide levels in the atmosphere. - Carbon dioxide dissolves in ocean water and returns to the atmosphere when it spontaneously comes out of solution. - Carbon leaves the water when it enters aquatic food chains via photosynthesis and biosynthesis (HCO3- converted to CaCO3 in the skeletons of diatoms, phytoplankton, crustaceans and shellfish). - The carbon is returned to the water when aquatic organisms respire.

Ozone in the Stratosphere

Ozone (O3) shields the earth's surface from much of the ultraviolet radiation reaching the earth from the sun. - Ultraviolet rays can cause skin cancer, cataracts, and may depress the immune system. - Although some of the recent depletion of ozone in the stratosphere was probably due to natural causes (volcanic eruptions, fewer sunspots), some is most likely caused by manmade chlorofluorocarbons (CFCs). - These gases escape from such sources as aerosol spray cans, leaky or discarded refrigeration units, insulation in transformers and a variety of industrial processes.

Inorganic to Organic Conversion Processes (Producers)

Photosynthesis and some Chemosynthesis

Atmosphere and biota

The atmosphere plays a central role in the carbon cycle. - Here, carbon is found as carbon dioxide. - Atmospheric carbon dioxide enters terrestrial food chains through plants when they perform photosynthesis. - Some of the carbon picked up by plants returns to the atmosphere as carbon dioxide when plants respire. - The rest of the carbon is used to build plant tissues. - The carbon then either moves through the food chain, beginning with herbivores when they eat plants, or to decomposers, when plants die. - Animals and decomposers return the carbon to the atmosphere as carbon dioxide when they cellular respirate.

Carbon Accounting

There are several different forms of carbon that we have to keep track of in learning about the carbon cycle.The main forms are: (a) Inorganic-C in rocks and oceans (such as bicarbonate and carbonate); (b) organic-C (such as carbohydrates found in organic plant and animal material); and (c) carbon gases such as CO2, (carbon dioxide), CH4, (methane), and CO (carbon monoxide).

Pathways and Cycling

There are several pathways in the carbon cycle that are of particular importance. The main pathways to and from the atmosphere are: - diffusion into and out of the ocean, - photosynthesis which consumes CO2 from the atmosphere (an output from the atmosphere), - respiration which produces CO2 from the atmosphere (an input to the atmosphere), - the burning of fossil fuels and biomass which also produces an input of CO2 to the atmosphere. - Although the largest storage of carbon is in rocks, it is not available in short time periods.