Geochemistry and Physics of Ocean Circulation* 



W. S. BROECKER, R. D. GERARD, 

 M. EWING, and B. C. HEEZEN 



Lamont Geological Observatory, Columbia University, 

 Palisades, New York 



ONE of the problems faced in preparing this paper was that of 

 interpreting the scope of the topic. The broadest interpretation 

 would require a complete coverage of all approaches to the problem 

 of circulation in the deep sea, ranging from the classical density 

 methods to the exciting recent development of deep floats. It was 

 decided to restrict the paper to the use of radioactive isotopes as 

 indicators of oceanic mixing rates. 



The main features of the tracer method are well illustrated by 

 the following analogy. Let us assume that a red dye can be obtained 

 which has the unique property of losing its color intensity at an 

 exponential rate when mixed with water. If such a dye were added 

 at a constant rate to one point on the surface of a pool of water, 

 after a steady state had been achieved, one would observe a 

 distribution of color which would depend on the rate of mixing 

 within the pool. If the pool were mixed far more rapidly than the 

 dye decayed, the color would be nearly uniform. If, on the other 

 hand, the mixing rate were far slower than the decay rate, the 

 color would be far more intense at the point of addition than in 

 the extremities of the pool. Computation of the precise time 

 relationships in such a system is complicated, however, by the 

 fact that the color of a given sample of water would be from many 

 little packets of dye each of which had spent different amounts of 

 time in the system. For this reason time estimates computed from 

 color contrast with the source using the simple exponential decay 

 relationship would be ambiguous. 



Lamont Geological Observatory, Columbia University, Contribution No. 440. 



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