10 



STUIVER 



SURFACE 



t = 9 years 



i 

 DEEP 



t = 1650 years 



(a) 



P 

 



L 

 A 

 R 



SURFACE 



t = 10 years 

 -4 



DEEP 



P 

 



L 

 A 

 R 



t = 1 850 years 



(b) 



t = 70 years 



t = 70 years 



(c) 



SURFACE 

 t = 16 years 



DEEP ' 

 PACIFIC 

 & INDIAN 



1050 years 



A 

 N 

 T 

 A 

 R 

 C 

 T 

 I 

 C 



t = 65 years 

 (d) 



t = 35 years 



SURFACE 



' f f yy p r r p r r I / r r r r i > > } 9 I / 



VttyMMU TH E R MOC L I N E V/YA 



DEEP ~ 

 ATLANTIC 





400 years /\ / t ~ 1360 years 



C 

 (e) 



DEEP 



PACIFIC 



& INDIAN 



Fig. 1 Some examples of oceanic circulation box models. The directions 

 of exchange are shown by solid arrows; wavy lines give particulate transport. 

 The calculated residence times, r, are inside each reservoir. The relative 

 dimensions of the boxes are not identical with the actual ratios of reservoir 

 sizes. Ocean— atmosphere exchange has been omitted, (a) Two-layer 

 model. 1 * 11 (b) Outcrop model. 12 (c) Three-reservoir model. 13 (d) World- 

 ocean model. 1 3 (e) Simplified mixing cross model. 1 4 



model, 1,11 (2) the outcrop model, 12 (3) the three-reservoir model, 13 (4) the 

 world-ocean model, and (5) the mixing cross model. All models incorporate 

 a well-mixed surface-layer reservoir and a much larger deep-ocean reservoir. The 

 oceanic deep-water masses are fed by waters sinking in the polar regions; this has 

 been taken into account (1) in the outcrop model by having the deep water 

 reaching the surface over a portion of the oceans, (2) in the three-reservoir and 

 mixing cross model through a well-mixed reservoir at the end of the oceans, and 

 (3) in the world-ocean model through two reservoirs of vertical mixing (Arctic 

 and Antarctic). For each model, the mixed-surface-layer depth is taken as 

 100 m; the calculated residence times are given in the figure. Mixing is assumed 

 to take place only as indicated by the arrows; for instance, in the world model 

 [Fig. 1(d)] a cyclic flow is postulated for the Atlantic and no direct mixing 

 between the surface and deep reservoirs. 



A comparison of the box models with the much more complicated 

 water-mass structure of the oceans clearly indicates a large degree of over- 

 simplification. The overall features of the models, however, lead to some 

 important general conclusions. For instance, residence times for the Pacific and 



