GEOCHEMISTRY AXD PHYSICS OF OCEAX CIRCULATION" 



313 



Figure 7 sho^vs the C^^ data for the central waters plotted on a 

 T-S diagram. Note for the South Atlantic central waters (SACW) 

 that the AC^^ values are lower for lower temperatures. This is 

 consistent with the pattern observed in the surface waters at the 

 southern end of the ocean, therefore lower C^^ for lower 

 temperature. 



Crude ages can be assigned to the deep waters of the Atlantic 

 in the following way. If it is assumed that the deep water at the 

 time of descent had a C^^ concentration the same as that observed 

 today in the source region for the mass, the mean residence time 

 of water in the mass can be estimated from the difference between 

 the value at the surface and that characterizing the mass at depth. 

 Such residence times for deep waters originating in the North 

 Atlantic are given in Table VI. At best the estimates may be good 

 to + 100 years, and at worst they probably represent maximum 

 estimates of the residence time. With the exception of the central 

 water and the C^^ maximum layer, the times are close to 500 years. 



18- 



16- 



O 



o 14 



»- 



< 12 

 oc 



LJ 



a. 



UJ 



10 



8 



34.8 35.0 35.2 35.4 35.6 35.8 36.0 36.2 36.4 36.6 

 SALINITY 



Fig. 7. aC^^ results for samples from the central water systems as a function 

 of temperature and salinity. 



