14 C CYCLE AND ITS IMPLICATIONS FOR MIXING RATES 17 



As discussed previously, the mixing-cross-model studies indicate a CaC03 

 production rate of 1.4 g cm -2 1000 years" for the Pacific Ocean. The total 

 carbon flux, including organic carbon, is five times larger and would be 

 equivalent to B = 5 X 10 3 cm 3 C0 2 produced annually in 1 liter of water for an 

 average water column of 3500 m length. This value, when combined with the 

 B/w value derived from the preceding total CO2 data, yields a vertical advection 

 velocity, w, of 4 m/year. With a value of 1 km for the mixing parameter, the 

 corresponding value for the eddy-diffusion coefficient K is 1.3 cm 2 /sec. 



The values obtained for K, w, and B in the preceding manner can be applied 

 to Eq. 1 describing the 14 C concentration in the deeper Pacific waters. (See 

 Craig 20 for more detailed discussion.) The particulate flux produces a 14 Cflux 

 equal to the product of the particulate flux and the specific i C activity of the 

 material transported downward. Isotope fractionation causes, as discussed, a 3% 

 depletion in C of B relative to surface ocean water, whereas the ocean surface 

 waters are depleted by about 4% in 14 C when compared with the modern * C 

 oxalic acid standard. 



The actual profiles of the absolute 14 C concentration for the few available 

 data in the deeper waters appear nearly constant in the deep Pacific, with a 

 random scattering of about ±1.5%. When the general solution of Eq. 1 is applied 

 to the data, a best fit is obtained for w = 5 m/year. However, the scattering of 

 the measured points is relatively large; as a result, any value of w in the range of 

 2 to 20 m/year fits the data. 



The near constancy of C concentrations in the deeper Pacific and the 

 nearly similar value of l C concentrations in the thermocline layer indicate, as 

 already mentioned, a lack of net transport of 14 C through advection and 

 diffusion between those reservoirs. 



Essentially Eq. 1 is simplified to C* = constant and B* = AC* (C* = 14 C 

 concentrations). The biotic production rate B can be calculated from this 

 relation and also w through the B/w ratio obtained from total C0 2 profiles. 



A more detailed analysis of the l C concentration profiles will only be 

 possible when both specific 14 C activities and total C0 2 concentrations become 

 available with a precision of 0.5% or better. Until then the 14 C profiles 

 contribute in the advection— diffusion model only limited knowledge to the 

 parameters associated with mixing processes in different parts of the Pacific 

 Ocean. 



The bottom waters in the oceans contain the horizontal water flux that 

 provides the vertical advection flow in the one-dimensional advection— diffusion 

 model. As mentioned, the reduction in specific 14 C activity of 3- to 4-km-deep 

 water, when moving from the South to the North Pacific, indicates northward 

 velocities of about 0.6 mm/sec, according to Bien and coworkers. 1 7 This 

 calculation is valid when the bottom waters can be considered a closed system, 

 with the only changes in C activity provided by radioactive decay and by 

 addition of C0 2 from oxidation of organic material in situ. In the advection— 



