Buffer factor

Fig. 11-8 Isolines of pH (a), Pco (b). and the Buffer factor (c) plotted as functions of DIC and alkalinity. The lines have been calculated for a temperature of 15 C and a salinity of 35% . The equilibrium constants for Ki and K2 are from Mehrbach et al. (1973), Kq from Hansson (1973) and B calculated from salinity according to the formula given by Culkin (1965).

The Revelle factor is about 10 for typical surface seawater. The details of the chemistry of this general relationship and its derivation have also been discussed by Sundquist et al. (1979), who called it the "homogeneous buffer" factor. Of interest is the fact that using the Revelle factor one can calculate for an instantaneous change in the Pco2 °f the atmosphere, the distribution of carbon between the atmosphere and seawater. 

Sundquist E.T., Plummer L.N. and Wigley T.M.L. (1979) Carbon dioxide in the surface ocean The homogeneous buffer factor. Science 204,1203-1204. 

As discussed above, the chemistry of carbon in seawater is such that less than 1% of the carbon exists as dissolved CO2. More than 99% of the DlC exists as bicarbonate and carbonate anions (Table 3). The chemical equilibrium among these three forms of DlC is responsible for the high solubility of CO2 in the oceans. It also sets up a buffer for changes in oceanic carbon. The buffer factor (or Revelle factor), is dehned as follows ... 

The buffer factor. The oceanic buffer factor (or Revelle factor), by which the concentration of CO2 in the atmosphere is determined, increases as the concentration of CO2 increases. The buffer factor is discussed above in Section 8.10.3.1.3. Here, it is sufficient to describe the chemical equation for the dissolution of CO2 in seawater. 

An Equilibrium Approach The Uptake of CO2 by the Ocean and the Buffer Factor... 

We are already acquainted with the mass law equations that connect atmospheric CO2 and surface waters. We have seen in Example 7.8 that ocean surface water is markedly supersaturated with respect to CaC03 thus the addition of CO2 does not cause any CaC03 dissolution. Hence the buffer factor in equation 27 can be evaluated under conditions of constant alkalinity. This problem has also been examined in Example 4.10. 

With the results displayed in Figure 15.21, a buffer factor, rj = 9.7 (15°C), is obtained for a change in pcoz from 2.7 x lO " to 3.0 X 10" atm in other words, for an increase of 10% in pco2 increases by 1 %. The buffer factor increases with increasing Pco2 io example, if pco2 is increased from 3.3 x... 

If all fluxes were proportional to the reservoir content, i.e. if the buffer factor had been unity, all reservoirs would be equally affected 15% in the 6000-Pg case and 2.5% in the 1000-Pg case. 

The buffer factor has the consequence that the exchange coefficient fcma associated with the dissolution equilibrium between atmosphere and mixed layer must be replaced by /cma when the equilibrium is perturbed. The uptake capacity of the mixed layer is reduced to one-tenth of its equilibrium value, and the relaxation time for the transfer of excess C02 toward the deep ocean, given by Eq. (11-14) for a pulse input, is raised to r2 =220yr. This is an important result. It shows that it takes several centuries to drain from the atmosphere the excess of C02 injected by the combustion of fossil fuels. It makes little difference that combustion must be represented by a continuous source function, because any continuous function can be expressed by a time series of pulses. In the box-diffusion model of the ocean discussed by Siegenthaler and Oeschger (1978), the response to a pulse input leads to a nonexponential decay of atmospheric C02, which after equilibration with the mixed layer is somewhat faster than that in the two-box model treated here, but the time scales are still roughly the same. 

Solid carbonate precipitation/dissolution are included as kinetic processes to the overall DOC biodegradation reactive model depending on the actual saturation. Further TIC (total inorganic Carbon) and the Calcite solubility equilibrium (dissolved Calcium and solid Calcite) are considered as main pH buffering factors. The actual... 

The ratio of the instantaneous fractional change in the partial pressure of C02 (pC02) exerted by seawater to the fractional change in total C02 dissolved in the ocean waters. The buffer factor relates the partial pressure of C02 in the ocean to the total ocean C02 concentration at constant temperature, alkalinity and salinity. The Revelle factor is a useful parameter for examining the distribution of C02 between the atmosphere and the ocean, and measures in part the amount of C02 that can be dissolved in the mixed surface layer, rocketsonde... 

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