Carbon cycle reservoirs

Fig. 11-18 A four-box model of the global carbon cycle. Reservoir inventories are given in moles and fluxes in mol/yr. The turnover time of CO2 in each reservoir with respect to the outgoing flux is shown in brackets. (Reprinted with permission from L. Machta, The role of the oceans and biosphere in the carbon dioxide cycle, in D. Dryssen and D. Jagner (1972). "The Changing Chemistry of the Oceans," pp. 121-146, John Wiley.)...

Figure 2. The marine carbon cycle. Reservoir sizes, flux estimates, and isotopic values are presumed to be representative of the Phanerozoic. The short-term carbon cycle is enclosed within the dashed box. The dashed line from the short-term carbon cycle to the organic reservoir represents the slow leak of biosphere organic carbon that supplies the long-term organic carbon reservoir. Reservoir sizes in Gmoles fluxes in Gmole/ky.

The great virtues or attributes of are that (1) it is a carbon isotope, and is introduced in to the carbon cycle reservoirs as carbon dioxide in the earth s atmosphere, and (2) its half-life is well suited to study late Quaternary events and processes, including dating of sediments and timing of deep and bottom water formation. 

Figure 1. The global carbon cycle. Estimates of reservoir size and annual fluxes are from Post et al. (4), Vegetation carbon reservoir was estimated from latest carbon density estimates. All values except the atmospheric reservoir are approximate only. All values are in gigatons. Fluxes are next to the arrows and are in gigatons ear.

The most common way in which the global carbon budget is calculated and analyzed is through simple diagrammatical or mathematical models. Diagrammatical models usually indicate sizes of reservoirs and fluxes (Figure 1). Most mathematical models use computers to simulate carbon flux between terrestrial ecosystems and the atmosphere, and between oceans and the atmosphere. Existing carbon cycle models are simple, in part, because few parameters can be estimated reliably. 

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... 

Fig. 4-3 Principal reservoirs and fluxes in the carbon cycle. Units are 10 g (Pg) C (burdens) and PgC/yr (fluxes). (From Bolin (1986) with permission from John Wiley and Sons.)...

Fig. 10-16 A simple schematic of the carbon cycle. Part (a) is the pre-industrial case, and part (b) shows the contemporary reservoirs and fluxes, in Pg C and Pg C/yr, respectively (Pg C = lO g C). This diagram of the carbon cycle is similar to those presented in Chapters 4 and 11. (Reprinted by permission from Nature (1993). 365 119-125, Macmillan.)...

This treatment of the carbon cycle is intended to give an account of the fundamental aspects of the carbon cycle from a global perspective. After a presentation of the main characteristics of carbon on Earth (Section 11.2), four sections follow 11.3, about the carbon reservoirs within the atmosphere, the hydrosphere, the biosphere... 

Although the largest reservoirs of carbon are found in the lithosphere, the fluxes between it and the atmosphere, hydrosphere, and biosphere are small. It follows that the turnover time of carbon in the lithosphere is many orders of magnitude longer than the turnover times in any of the other reservoirs. Many of the current modeling efforts studying the partitioning of fossil fuel carbon between different reservoirs only include the three "fast" spheres the lithosphere s role in the carbon cycle has received less attention. 

The freshwater cycle is an important link in the carbon cycle as an agent of erosion and as a necessary condition for terrestrial life. Although the amount of carbon stored in freshwater systems is insignificant as a carbon reservoir (De Vooys, 1979 Kempe, 1979a), about 90% of the material transported from land to oceans is carried by streams and rivers. 

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. 

As partly mentioned before, natural and anthropogenic induced variations of the atmospheric C02 concentration and of the 14C/ 12C and 13C/12C ratios have been observed. For a quantitative discussion of these variations in relation to possible causes, models for the carbon cycle dynamics have been developed [21-25]. Compared to the noble gas radioisotopes 39Ar and 81Kr, for which we only have to consider a well mixed atmospheric reservoir, we have a much more complicated system for 14C. The C02 in the atmosphere exchanges with the carbon in the biosphere and with the... 

Additional material on this subject is provided in the supplemental information for Chapter 25.4 that is available online at http //elsevierdirect.eom/companions/9780120885305. Key topics covered are the role of tectonism in the geologic carbon cycle and how the evolution of pelagic calcifiers in the Phanerozoic led to the development of feedbacks, some stabilizing and some destabilizing, that act on the atmospheric COj reservoir. Also included is a short summary of how the global carbon cycle interacts with the atmospheric O2 and sulfur cycles. 

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