The Major Reservoirs of Carbon

Approximately 1% of the atmospheric carbon cycle is maintained by methane (Ehhalt, 1974). Global background levels of CH4 are estimated at 

7 ppmv, which corresponds to 3Pg C (Blake and Rowland, 1988). Sources of methane are found in the sea and on land however, the main sink for methane in the atmosphere is oxidation by the hydroxyl radical ( OH). 

Oxidation of methane is one of the sources of atmospheric CO. Another internal source of importance is the oxidation of terpenes and isoprenes emitted by forests (Crutzen, 1983). The carbon monoxide concentration in the atmosphere ranges from 0.05 to 0.20 ppmv in the remote troposphere (with considerable differences between the northern and southern hemispheres), which means that about 0.2 Pg of carbon is present as CO in the atmosphere. 

Apart from CO2, CH4, and CO, there are many other gases in the atmosphere that contain carbon terpenes, isoprenes, various compounds of petrochemical origin, and others. We will not discuss them further, although some, like dimethylsulfide [DMS (CH3)2S], are of great importance in the bio-geochemical cycles of other elements. The total amount of atmospheric carbon in forms other than the three discussed is estimated at 0.05 Pg C (Freyer, 

280 ppmv. Fossil fuel emissions (Marland and Boden, 1991 Marland and Rotty, 1984 Marland et al, 1989 Rotty, 1981) are well known the trade in coal and oil has considerable economic value and is therefore well documented. Assuming that all fossil fuel produced is oxidized within a few years from its removal from the ground, a good estimate of the total emissions can be made. During the past decades there has been an average observed airborne fraction of about 0.55. (The observed airborne fraction is defined as the observed CO2 increase divided by the amount produced by fossil fuel combustion.) Since this quantity does not take any biospheric influences into account, it has limited value, although its use is widespread. 

Greenland (Neftel et al, 1982 Barnola et ah, 1983 Etheridge et al, 1996) give the least criticized data and indicate a value of 280 + 10 ppmv (see Fig. 11-5). 

Oxidation of methane is one of the sources of atmospheric CO. Another internal source of importance is the oxidation of terpenes and 

A detailed characterization of DOC is difficult to make a large number of compounds have been detected but only a small portion of the total DOC has been identified. Identified species 

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The quantity of dissolved organic carbon in the oceans has been estimated to be about 1018 g and constitutes one of the major reservoirs of organic carbon. Although large in total mass, the concentration of organic carbon in seawater is low (typically 0.5 -1.5 mg C per litre). 

Kvenvolden, K.A. (1988). Methane hydrate - a major reservoir of carbon in the shallow geosphere. Chemical Geology, 71 (1-3), 41-51. 

From Figure 9.1, it can be seen that the major form of carbon in the atmosphere is C02(g), constituting over 99% of atmospheric carbon. Carbon dioxide makes up 0.035% by volume of atmospheric gases, or 350 ixatm = 350 ppmv. The atmosphere has a mass of CO2 that is only 2% of the mass of total inorganic carbon in the ocean, and both of these carbon masses are small compared to the mass of carbon tied up in sediments and sedimentary rocks. Therefore, small changes in carbon masses in the ocean and sediment reservoirs can substantially alter the CO2 concentration of the atmosphere. Furthermore, there is presently 3 to 4 times more carbon stored on land in living plants and humus than resides in the atmosphere. A decrease in the size of the terrestrial organic carbon reservoir of only 0.1% y-1 would be equivalent to an increase in the annual respiration and decay carbon flux to the atmosphere of nearly 4%. If this carbon were stored in the atmosphere, atmospheric CO2 would increase by 0.4%, or about 1 ppmv y-l. The... 

The major reservoirs of C are stored in the Earth s crust, with much of it as inorganic carbonate and the remaining as organic C (e.g., kerogen). 

The rapid increase in the atmospheric reservoir of carbon dioxide (CO2) is one of the dramatic realities of our times. Equivalent today to over 720 gigatonnes (Gt) of carbon, the reservoir is increasing at almost 3 Gt per annum ( ), or about 0.4 per cent per annum. Since carbon dioxide is a raw material for photosynthesis and a radiatively significant gas, this increase has major implications for climatologists and biologists. It also... 

Thus, there are two major reservoirs of carbon in the Earth carbonate and organic compounds. It should be stressed that both are of biotic origin. Non-biotic carbonates, for instance, from volcanoes, are the rare exception of the rule. A connecting link between the carbonate and organic species is CO2, which serves as an essential starting material for both the photosynthesis of organic matter and the microbial formation of carbonates. 

Among the carbon reservoirs of the biosphere, a large proportion is stored in soil organic matter and marine sediments (Bolin, 1977). The accumulation of carbon in soils and sediments is a function of the organic carbon balance between net primary production (carbon fixation) and heterotro-phic metabolism (decomposition). The fixation of atmospheric carbon through photosynthesis is the major sonrce of carbon to terrestrial, wetland, and aquatic ecosystem. 

At the ecosystem scale, POM is generated through litter fall (in forested wetlands) and detrital production. This is the major reservoir of organic carbon above the soil surface and constitutes approximately 95% of the total carbon. The POM is broken down into simple readily utilizable organic forms, followed by simultaneous mineralization to inorganic carbon. 

Kaiser, K., and Benner, R. (2008). Major bacterial contribution to the ocean reservoir of detrital organic carbon and nitrogen. Limnol. Oceanogr. 53, 99-112. 

To the extreme right of Figure 9.1 is the major gaseous reservoir of carbon in the atmosphere—CO2. The residence time (x) of about 6 years means that the gas should be reasonably well-mixed in the atmosphere, but there is a small gradient in mean concentration from the northern hemisphere to the southern. The residence time is calculated with respect to total organic productivity (although the system is not at steady state and X changes with time) ... 

There are 5 major reservoirs in the Earth system atmosphere, biosphere (vegetation, animals), soils, hydrosphere (oceans, lakes, rivers, groundwater), and the lithosphere (Earth crust). Elemental cycles of carbon, oxygen, nitrogen, sulfur, phosphorus, and other elements interact with the different reservoirs of the Earth system. The carbon cycle has important aspects in tropical forests due to the large amount of carbon stored in the tropical forests and the high rate of tropical deforestation 0acob 1999)-... 

The major disadvantage of solid phase extraction is that it provides a chemically biased view of the DOM reservoir, and seems to preferentially extract compounds with relatively low amounts of N. Other problems include sample contamination by various resins and incomplete elution of adsorbed DOM. SoHd phase extraction remains, however, the only technique capable of reproducibly isolating DOM compounds within the entire range of MWs. Furthermore, the radiocarbon content (A " C) of DOC isolated by XAD resins is depleted relative to the total dissolved inorganic carbon (DIG) reservoir values for XAD isolates are between —300... 

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