Organic carbon global reservoirs

Figure 1 The global organic carbon cycle. Numbers in parentheses are approximate reservoir sizes (10 g C = Gt) and italicized are approximate fluxes (10 gCyr ). Nonitalicized numbers are approximate ranges for stable carbon isotopic compositions (S C, per mil) and italicized numbers are approximate radiocarbon ages...

The reduction is typically limited by the availability of organic carbon and often occurs in shallow waters at continental margins. Thus, global sulfide production would be dependent on the availability of biological productive areas over geological time. Sulfur-isotope data can be used to constrain simple models of the sulfur cycle over geological time and establish the size of the reservoirs as shown in Figure 5(b). 

Figure 15.18. Comparison of global reservoirs and their residence times (t in years) (Example 15.3). The reservoirs of the atmosphere, of surface fresh waters, and of living biomass are significantly smaller than the reservoirs of sediment and marine waters and are thus more susceptible to distuibance. For example, the combustion of fossil fuel (from the reservoir of organic carbon in sediments) will have an impact on the smaller reservoirs CO2 in the atmosphere will be markedly enlarged. This combustion also fixes some N2 to NO and NO2 sulfur, associated with the organic carbon, introduces CO2 into the atmosphere. These nitrogen and sulfur compounds are washed out relatively rapidly into soil and aquatic ecosystems. The total groundwater reservoir may be twice that of surface fresh water but, however, is less accessible. (From Stumm, 1986.)...

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).)...

The ocean is one of the largest reservoirs of organic (biogenic) carbon on the earth s surface [1]. Globally, the composition of this reservoir is regulated by feedback mechanisms that maintain the planetary environment within the relatively narrow range necessary for life [2,3]. Phytoplankton productivity is the ultimate source of organic carbon in the ocean [4] the best estimate of this primary production is 45-50 Gt C year [5] - about half of the combined total for terrestrial and marine productivity [1]. 

The global rate of carbon burial is 50 x 10 mol per year, four parts carbonate and one part organic carbon. The residence time of the combined surface carbon and carbonate reservoirs is 67,000 years. During this time, a carbon atom is in CO2 for 66,000 years and in the biomass for 1000 years. It gets oxidized and reduced 165 times. This example indicates that organic carbon burial cannot be... 

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