Carbon reservoirs sedimentary rocks

From Eqn 6.6 it can be seen that the geological record of 813C for kerogens and carbonates reflects changes in the sizes of C reservoirs, in addition to changes in the relative importance of the various fractionation pro-cesses (such as C3 photosynthesis). Because the kerogen and carbonate in sedimentary rocks dominate the shallow reservoirs (>99.9%), the isotopic mass balance in Eqn 6.6 can be written simply as ... 

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... 

This definition of a geochemical cycle demonstrates that recognizing the appropriate scale of the cycle is vital. Particularly important is the timescale. It is clear that on short timescales catastrophic transfers may take place between reservoirs which on a longer timescale would be "smoothed out." As has already been noted, the appropriate choice of timescale is particularly pertinent to a consideration of the carbon cycle (see Kump et al., 1999), for whether or not the sedimentary rock... 

The vast majority of carbon is found in sedimentary rocks as inorganic carbonate minerals and solid organic compounds, and in the deep interior as carbon dioxide and methane. The global carbon cycle can therefore be envisioned as the long-term transfer of deep crustal and mantle carbon to shallow crustal sediment reservoirs via the ocean/atmosphere system, where carbon is parsed into several reservoirs through reactive pathways that modify the initial carbon isotopic value of the outgassed carbon. The... 

Carbon is exchanged among the atmosphere, oceans, the terrestrial biosphere, and sediments and sedimentary rocks, the latter two more slowly than the other reservoirs. The more rapid components of the cycle are shown in Figure 21.11. During the preindustrial period, when the carbon cycle can be assumed to have been in balance, 98.1% of the CO2... 

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