Chapter 11 



ISOTOPIC TRACER TECHNIQUES FOR MEASUREMENT OF PHYSICAL 

 PROCESSES IN THE SEA AND THE ATMOSPHERE^ 



Harmon Craig, Scripps Institution of Oceanography, University of California, 



La Jolla, California 



I. Introduction 



Throughout this report reference has been 

 made to the need for a fundamental understand- 

 ing, on a long-term basis, of mixing phenomena 

 in the ocean and the atmosphere. In a general 

 sense the ocean and the atmosphere may be re- 

 garded as a two-phase system, in which the 

 phases are separated by the fundamental dis- 

 continuity of the ocean-atmosphere interface. 

 Each phase is further divided into two parts by 

 a second order discontinuity; the atmosphere, 

 divided by the tropopause at about 12 km, into 

 the troposphere and the stratosphere, etc., and 

 the oceans, divided by the thermocline at some 

 100 meters, into an upper and lower layer. 



The basic problems in determining the effects 

 of both radioactive waste disposal and the dis- 

 persal of debris from nuclear explosions may be 

 formulated in terms of a single objective. Given 

 the ocean-atmosphere system under normal 

 steady state conditions, and given some sub- 

 stance introduced at any point in one of the 

 four designated zones, we wish to be able to 

 predict quantitatively the concentration of the 

 substance as a function of latitude, longitude, 

 altitude or depth, and time. These problems 

 thus involve studies of (1) the intra-phase mix- 

 ing, above, below, and across the second-order 

 discontinuities within each phase, and (2) the 

 inter-phase mixing across the ocean-atmosphere 

 interface, with the aim of predicting the effects 

 of perturbations on the system. 



The dominant mixing processes in the vari- 

 ous spheres are processes of mass movement or 

 turbulent mixing. In such processes, for ele- 

 ments undergoing no change of phase, there is 

 little or no separation of components, and thus, 

 in general, isotopic tracer techniques may in- 



1 Contribution from the Scripps 

 Oceanography, New Series, No. 902. 



Institution of 



volve a wide range of materials of quite differ- 

 ent chemistry. It is this phenomenon of mass 

 movement dominance, and the relative unim- 

 portance of diffusive transfer except in special 

 cases, that makes the tracer technique so power- 

 ful; a tagged isotope for each element is not 

 required, and one can choose for each particular 

 study the elements most useful for tracing the 

 movement of a mass of heterogeneous material. 



As mentioned at several points in this report, 

 both artificial and natural isotopic tracers may 

 be used for the study of transfer phenomena in 

 the sea and the atmosphere. Artificial tracers 

 are of value in such studies because they allow 

 the investigator to introduce perturbations in 

 the system at convenient times and places; they 

 are especially valuable for the study of short 

 term fluctuations in local systems. However, for 

 the general understanding of mass transfer phe- 

 nomena, artificial tracers are of value mainly as 

 experimental checks on deductions based on 

 other data, with the exceptions of a few special 

 cases to be described below. The reason for this 

 is that mass transfer phenomena are by nature 

 subject to long term periodic fluctuations such 

 as convection, with periods often longer than 

 the time range available for observation. A sec- 

 ond reason for this is the high cost of radioiso- 

 topes and the large amounts of activity required 

 to tag adequately the large masses of water nec- 

 essary for ocean studies. 



Revelle, Folsom, Goldberg and Isaacs (1955) 

 have discussed in their Geneva report the prob- 

 lems involved in adapting radioisotope tracer 

 techniques to transfer studies in the ocean, and 

 the requirements for usable isotopes. If one 

 introduces some 10 curies of a gamma emitter 

 in solution at some point below the thermocline, 

 it is found that within a reasonable duration of 

 observation time the activity will be concen- 

 trated in a layer of the order of 1 meter thick 



103 



