Global carbon reservoirs

Figure 3 Global carbon reservoirs and annual fluxes. Units are gigatons of carbon in the reservoirs and Gt C yr for fluxes...

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.

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... 

Figure 3.2. Global carbon reservoirs, fluxes, and turnover times.

In these models the increase in the number of factors considered is clearly observed, as is the respective increasing adequacy that accompanies them. One of the first and sufficiently complete models of the global C02 cycle is the model proposed by Bjorkstrom (1979) which takes into account the dynamic interaction between carbon reservoirs in the biosphere and fluxes between them. For the first time, a unit for the World Ocean was realistically represented. In this unit the ocean is... 

Figure 3.6. A block diagram of the global biogeochemical cycle of carbon on Earth. Carbon reservoirs and fluxes are described in Table 3.3.

Martian meteorites provide no direct information on the geochemistry of martian sediments. However, SNCs have higher Ca/Si ratios than martian soils. Rubin et al. (2000) suggested that the lower Ca/Si in soils might indicate removal of calcium into a global carbonate reservoir. 

Productivity and C-isotope records—Attributing trends in bulk S Corg only to the trade-off between dominance of respiration-influenced local carbon reservoirs versus dominance of production-influenced global carbon reservoirs is clearly a gross oversimphfication, as a number of other factors may influence C-isotope fractionation in the biogenic and aqueous reservoirs of the carbon cycle. However, this hypothesis finds support in the observations of Cretaceous and Devonian basins summarized herein. In each of these case studies, relative depletion of S Corg values are observed in association with units interpreted to represent examples of the anoxia-nutrient feedback mechanism, and recycling of... 

The rate of global production of bicarbonate by weathering can be determined because we loiow approximately the flow of HCO J in the world s major rivers. This represents a drain of the CO2 of the atmosphere, which must be balanced by resupply to maintain a steady One is tempted to estimate the vulnerability of atmospheric/co to the imbalance between the atmospheric CO2 drain by weathering and resupply by CaCOs precipitation by focusing on the CO2 fluxes from and to the atmosphere. This, however, would be incorrect because the ocean and atmosphere carbon reservoirs are approximately in chemical equilibrium on time scales greater than the circulation of the ocean (see Chapter 11). In order to emphasize the severity of the HCOs imbalance estimated in Fig. 2.4 one should focus on the fluxes of DlC and alkalinity between the land and ocean. Because we have not yet discussed alkalinity and DIC relationships (Chapter 4) a simple approximation can be made by considering the fluxes of bicarbonate and calcium. 

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. 

Table 13. The major global carbon reservoirs (based on Dobrovolsky. 1994).

This chapter summarizes the most recent compilations of carbonate reservoir size in the ocean and sediments, as well as the particulate and dissolved fluxes (Fig. 9.5) provided by the above mentioned authors. Coral reefs are probably the best documented shallow-water carbonate environment. Carbonate production on reef flats range as high as 10.000 g CaCOj m yr , with a global mean of about 1800 g CaCOj myr . Totally this amounts to 24.5 10 molyr (Table 9.1) from which 14.5-10 mol yr accumulate and 10-10 mol yr are transported to the deep-sea either by particulate or dissolved export. One of the most uncertain numbers in all these budget calculations are the estimates of the global carbonate production in... 

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... 

Figure 1 Major global reservoirs Involved in active production, exchange and cycling of organic carbon. Reservoir sizes are shown in Gt carbon (1 GtC = 10 g C). Numbers in parentheses are based on 1980s values numbers without parentheses are estimates of the pre-anthropogenic values. Fluxes primarily mediated by biological reactions are shown with dashed arrows physical transport processes are shown with solid arrows. (Modified after Siegenthaler and Sarmiento (1993) and Hedges and Oades (1997).)...

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