Carbon exchange reservoir

Radiocarbon is uniformly distributed in the carbon exchange reservoir. 

Budgets and cycles can be considered on very different spatial scales. In this book we concentrate on global, hemispheric and regional scales. The choice of a suitable scale (i.e. the size of the reservoirs), is determined by the goals of the analysis as well as by the homogeneity of the spatial distribution. For example, in carbon cycle models it is reasonable to consider the atmosphere as one reservoir (the concentration of CO2 in the atmosphere is fairly uniform). On the other hand, oceanic carbon content and carbon exchange processes exhibit large spatial variations and it is reasonable to separate the... 

The balance between calcium carbonate production and dissolution is the major pH buffering mechanism of seawater over periods of time at least on the order of thousands of years ( ). The atmospheric carbon dioxide reservoir is less than 2 percent the size of the seawater reservoir ( ) and there is active exchange between these two reservoirs across the air-water interface. Consequently, the carbon dioxide content of the atmosphere and accumulation of calcium carbonate in the deep oceans are closely coupled. 

The atmosphere is an important conveyor belt for many pollutants. The atmosphere reacts most sensitively to anthropogenic disturbance because proportionally it represents a much smaller reservoir than land and water furthermore, the residence times of many constituents of the atmosphere are smaller than those that occur in the other exchange reservoirs. Water and atmosphere are interdependent systems. Many pollutants, especially precursors of acids and photooxidants, originate directiy or indirecdy from the combustion of fossil fuels. Hydrocarbons, carbon monoxide, and nitrogen oxides released by thermal power plants and, above all by automobile engines, can produce, under the influence of sunlight, ozone and other photooxidants. 

In this example it was assumed that the carbon gas reservoir of a given 6 C was large in comparison to the C reservoir of the water and the solid phases and was in continuous isotopic exchange with these phases. If such a water becomes isolated from the gas reservoir and then interacts with calcite or dolomite, then the content of the solution will also depend on that of the dissolving carbonate rock. 

CARBON CYCLE refers to the continual transformation of carbon from one form to another, and its ceaseless transport from one place to another. Schematically, the transformation can be represented as conversions between inorganic and organic forms of carbon and the transport as redistribution within and exchanges among different reservoirs the atmosphere, vegetation and soils, oceans, and the lithosphere. This is presented in Fig. 1. CO2 is chemically inert in the atmosphere, and so its abundance is determined principally by its carbon exchanges with the land, ocean and lithosphere. 

FIGURE 1 Schematic diagram of the global carbon cycle, showing carbon exchanges among the different reservoirs. 

Information on the sources and sinks of CO2 can be obtained from variations of carbon isotopes. Carbon-13, a stable isotope, comprises approximately 1% the total inventory of carbon. Different carbon exchange processes have different degrees of fractionation or discrimination against the heavier isotope, so that the variations in the ratio of C C in the atmospheric terrestrial and oceanic carbon reservoirs provide additional information about the sources and sinks of atmospheric CO2. 

The carbon cycle is dynamic, and is fully interactive with the chmate. The earth s climate changes as a result of changes in the abundance of CO2 in the atmosphere climate change in turn changes the dynamics of carbon exchange among the reservoirs and causes shifts in the atmospheric CO2 levels. 

The cycles of carbon and the other main plant nutrients are coupled in a fundamental way by the involvement of these elements in photosynthetic assimilation and plant growth. Redfield (1934) and several others have shown that there are approximately constant proportions of C, N, S, and P in marine plankton and land plants ("Redfield ratios") see Chapter 10. This implies that the exchange flux of one of these elements between the biota reservoir and the atmosphere - or ocean - must be strongly influenced by the flux of the others. 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

The content of the material in a carbon reservoir is a measure of that reservoir s direct or indirect exchange rate with the atmosphere, although variations in solar also create variations in atmospheric content activity (Stuiver and Quay, 1980, 1981). Geologically important reservoirs (i.e., carbonate rocks and fossil carbon) contain no radiocarbon because the turnover times of these reservoirs are much longer than the isotope s half-life. The distribution of is used in studies of ocean circulation, soil sciences, and studies of the terrestrial biosphere. 

Keeling, C. D. (1973a). The carbon dioxide cycle. Reservoir models to depict the exchange of atmospheric carbon dioxide with the oceans and land plants. In "Chemistry of the Lower Atmosphere" (S. Rasool, ed.), pp. 251-329. Plenum Press, New York. 

Pearman, G. I. and Hyson, P. (1986). Global transport and inter-reservoir exchange of carbon dioxide with particular reference to stable isotopic distributions, /. Atm. Chem. 4, 81-124. 

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