Organic carbon total annual

Several authors have applied in situ pulse labeling of plants (grasses and crops) with C-CO2 under field conditions with the objective of quantifying the gross annual fluxes of carbon (net assimilation, shoot and root turnover, and decomposition) in production grasslands and so assess the net input of carbon (total input minus root respiration minus microbial respiration on the basis of rhizodeposition and soil organic matter) and carbon fixation in soil under ambient climatic conditions in the field. 

Jenkinson, D. S., and Coleman, K. (1994). Calculating the annual input of organic matter to soil from measurements of total organic carbon and radiocarbon. Eur. J. Soil Sci. 45, 167-174. 

From Figure 9.1, it can be seen that the major form of carbon in the atmosphere is C02(g), constituting over 99% of atmospheric carbon. Carbon dioxide makes up 0.035% by volume of atmospheric gases, or 350 ixatm = 350 ppmv. The atmosphere has a mass of CO2 that is only 2% of the mass of total inorganic carbon in the ocean, and both of these carbon masses are small compared to the mass of carbon tied up in sediments and sedimentary rocks. Therefore, small changes in carbon masses in the ocean and sediment reservoirs can substantially alter the CO2 concentration of the atmosphere. Furthermore, there is presently 3 to 4 times more carbon stored on land in living plants and humus than resides in the atmosphere. A decrease in the size of the terrestrial organic carbon reservoir of only 0.1% y-1 would be equivalent to an increase in the annual respiration and decay carbon flux to the atmosphere of nearly 4%. If this carbon were stored in the atmosphere, atmospheric CO2 would increase by 0.4%, or about 1 ppmv y-l. The... 

As more complete data sets for TOC and DOC appeared in the literature, more sophisticated estimates of the annual riverine fluxes of DOC and POC from the continents to the oceans were developed. Schlesinger and Melack (1981) used two approaches to estimate the annual riverine flux of organic carbon. First, they noted that, for about a dozen rivers for which data were available at that time, a log-log plot of the total annual organic carbon load versus the total annual... 

The overall contribution of chemoautotrophy in the contemporary ocean to the formation of organic matter is relatively small, accounting for <1 % of the total annual primary production in the sea. However, this process is critical in coupling reduction of carbon to the oxidation of low-energy substrates, and is essential for completion of several biogeochemical cycles. 

Organic Carbon and Productivity Of the total carbon fixed annually ( 120 X lO mol C yr ) nearly all is respired and oxidized. Only a very small fraction of the organic matter produced in the ocean accumulates in the sediments. On a geological time scale the organic carbon preserved in the sediments is eventually remineralized to CO2. 

The total annual primary productionby photosynthetic planktonic organisms in the modem world oceans has been estimated to be in the order of 30-50T0 tons of carbon (Berger et al. 1989 Hedges and Keil 1995). Oceanic carbon fixation is not evenly distributed, but displays zones of higher activity on continental margins... 

Most of the DOC in the ocean appears to be of marine origin, with terrestrial organic carbon accounting for only 1% of the total annual production [4]. Stable carbon isotope (fi C) ratios of marine DOC are in the range -20 to -33 ppt [25,26], very similar to the ratios measured for marine phytoplankton... 

---