Fossil carbon reservoir

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. 

The crust is the largest carbon reservoir in the crustal-ocean-atmosphere factory (8 x 10 Pg C including the sediments). Most of this carbon is in the form of inorganic minerals, predominantly limestone, with the rest being organic matter, predominantly contained in shale and secondarily in fossil fuel deposits (coal, oil, and natural gas). The oceanic reservoir (4 X lO" Pg C) and the terrestrial reservoir (2 to 3 x 10 Pg C) are both far smaller than the crustal reservoir. The smallest reservoir is found in the atmospheric, primarily as CO2 (preindustrial 6 x 10 Pg C, now 8 x 10 Pg C and rising). The flux estimates in Figure 25.1 have been constrained by an assumption that the preindustrial atmospheric and oceanic reservoirs were in steady state over intermediate time scales (millennia). 

Although the amount of carbon stored in the fossil fuel reservoir is a very small component of the total crustal reservoir, it is large in comparison to the atmospheric reservoir. By burning fossil fuels, we have greatly accelerated the rate at which this carbon is released back into the atmosphere. Once in the atmosphere, this remobilized carbon is then able to interact with the biospheric and hydrospheric reservoirs. 

Variability in the Amount of Carbon in Reservoirs. In addition to variations in the production and distribution of radiocarbon over time and within portions of various carbon reservoirs, variations may result in situations where carbon not in equilibrium with the contemporary standard values is added or removed from any reservoir. Two instances of this are well documented since they occurred within the last century as a result of human intervention. The first is known as the industrial or Suess effect and is caused by the combustion of fossil fuels beginning about 1890, resulting in a depletion of atmospheric activities by about 3% (76). A more recent occurrence has been called the atomic bomb or Libby effect. The detonation of nuclear devices in the atmosphere beginning in 1945 produced large amounts of artificial increasing the radiocarbon concentrations in the atmosphere by more than 100% in the Northern Hemisphere (77). Because of equilibration with the oceans, the levels have been diminishing steadily since the atmospheric testing was terminated by the major nuclear powers except France and the People s Repub-... 

The corresponding example of reservoirs is depicted in Table 1. This Table shows current estimates of the most important carbon reservoirs and averaged residence times for carbon in these pools. The lithosphere is the reservoir for the bulk of global carbon, with about 20% of this being in the form of fossil organic fuels. 

Figure 22.6 shows a six-compartment model of the carbon cycle due to Schmitz (2002). The quantities shown in parentheses in each compartment are estimates of the pre-industrial ( 1850) amount of carbon, indicated by the M, symbols, measured in petagrams (Pg C) in each reservoir. Since the amount of carbon in the aquatic biosphere and in rivers, streams, and lakes is negligible compared with those in the other reservoirs in Figure 22.6, these are omitted. The fossil fuel reservoir affects the global carbon cycle only as a source of carbon. Sediments are actually the largest carbon reservoir of all, but the fluxes of carbon into and out of sediments are so small that sediments can be neglected as a compartment over any realistic timescale. Estimates of the pre-industrial flux of carbon... 

At the preindustrial steady state, the perturbation fluxes, Ff = Fj = Fr = 0, and F2i - F12 + F31 — F13 + F51 - F15 + F61 = 0, so that dMx/dt = 0. The total amount of carbon stored in fossil fuels affects the carbon cycle only through the amount actually released to the atmosphere. Falkowski et al. (2001) have estimated that the fossil fuel reservoir contains 4130 Pg C. (The ratio of the estimated fossil fuel reservoir to the current atmospheric reservoir, 4130/788 = 5.2. Thus, if the entire estimated fossil fuel reservoir were added to the atmosphere with no carbon taken up by other reservoirs, the atmospheric concentration of C02 would increase by a factor of 6.2. This can be considered as an upper-limit estimate for increase of atmospheric CO2.)... 

The full compartmental model and numerical values of the coefficients are given in Table 22.1. It is assumed that all reforested land increases the terrestrial biota, so ar = 1.0. The value of ad = 0.23 is that suggested by Schmitz (2002) [Lenton (2000) proposed 0.27]. Initial values for all M, are the preindustrial values given in Figure 22.6. The preindustrial fossil fuel reservoir is assumed to have contained 5300 Pg carbon the actual value is not important, only the emission rate Ff(t). The model requires as input Ff(t), Fd(t), and Fr(t) from preindustrial times to the present. Ff(t) is obtained from the historical record of carbon emissions from fossil fuels Fd(t) is that for deforestation, expressed also in units of Pg C yr-1. Until very recently, reforestation, Fr, can be assumed to have been negligibly small. 

FIGURE 8.2 Carbon reservoirs and sinks. The resource base (the sum of reserves and resources) is used for fossil fuels [Rogner, 1997], The consumption box shows worldwide cumulative consumption of fossil fuels. The upper section of the atmosphere box shows the increase in CO2 since preindustrial times. The error bars are a rough summary of current knowledge and do not reflect systematic analysis of uncertainty. The upper bound for storage in aquifers is of the order 10,000 GtC. The oceanic capacity is based on an arbitrary upper limit to pH change of 0.3 surface ocean pH has already decreased by -0.1 due to anthropogenic CO2. 

An important issue that remains unresolved, because of the lack of adequate quantitative data on reservoirs and fluxes, is the location of the so called "missing" carbon. Missing carbon is the carbon added to the atmosphere from the burning of fossil fuel that cannot be accounted for by the measured increase in atmospheric concentration or by diffusion into the ocean (5). 

However, with "only" 1000 Pg emitted into the system, i.e. less than 3% of the total amount of carbon in the four reservoirs, the atmospheric reservoir would still remain significantly affected (20%) at steady state. In this case the change in oceanic carbon would be only 2% and hardly noticeable. The steady-state distributions are independent of where the addition occurs. If the CO2 from fossil fuel combustion were collected and dumped into the ocean, the final distribution would still be the same. 

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