18 STUIVER 



diffusion model with particulate flux, however, total 14 C concentrations have to 

 be taken into account. The reduction in specific * C activity in the deep Pacific 

 along the South— North traverse is accompanied by an increase in C0 2 content, 

 and the resulting total 1 C concentration is practically identical in these areas. 20 

 Since the vertical gradient of the C concentration is zero, the net addition of 

 14 C through diffusion and advection to the bottom waters is zero. In addition, 

 the change in total C concentration, when traveling from South to North, is 

 also zero. As a result, it is concluded that the 14 C flux provided by biotic 

 transport to the bottom waters during its travel time is equal to the loss of l C 

 through decay over the same interval. The change in specific activity during 

 travel from South to North is then mainly caused by diffusive C0 2 from higher 

 levels into the bottom waters. This results in an increase in total C0 2 but a lower 

 specific activity because specific C activities are slightly lower at higher 

 levels. The model implies shorter horizontal travel times and larger flow 

 velocities, as the reduction in specific activity is only partially due to in situ 

 decay. 



Water-circulation patterns at abyssal depths provide additional complications 

 for horizontal-flow-velocity calculations. Only the western boundary current 

 would provide a straight South— North trajectory over the equator for the deeper 

 portions of the Pacific. 



The advection— diffusion model is only valid if oxidation of organic material 

 from the particulate flux actually occurs in the deep ocean. Suess and 

 Goldberg 22 cite two studies 23,2 which show that this premise has to be 

 examined in more detail. The arguments involve (1) a correlation between 

 salinity and dissolved oxygen, indicating a lack of measurable effects of 

 respiration on the concentration of dissolved oxygen; and (2) the lack of 

 variability in the concentration of dissolved organic carbon in deep water which 

 would indicate that this material is highly resistant to oxidation. The conclusion 

 of Menzel and Ryther 23 is that the entire biochemical cycle of organic matter 

 appears to occur in the upper 300 m of the ocean. Craig, 25 ' 2 on the other 

 hand, discusses extensively the above-mentioned arguments and concludes that 

 in situ oxidation and solution of carbon in the Pacific occur at sufficient rates 

 for the applicability of the advection— diffusion model with particulate 

 transport. His main argument is the consistency of the calculated results with the 

 profiles obtained in the deep water for total CO2, 1 C, 1 C, 2 , and alkalinity. 



The controversy involving the biotic component for C transport in the 

 deep oceans has to be resolved before more refined interpretations of the C 

 distributions can be made. In one of the more recent articles, 2 7 it is concluded 

 that, until a large number of detailed profiles on total C0 2 , 14 C, * 3 C, alkalinity, 

 and 2 are accumulated, all interpretations of the present library of data should 

 be regarded as highly tentative and probably incorrect. Perhaps this conclusion 

 should be taken more seriously. 



