118 CAKRITT [CHAP. 5 



3. Water Tagging and Tracer Techniques 



Studies of the motion of sea-water encompass a very broad size spectrum 

 bounded on the small end by molecular phenomena and on the large end by 

 entire oceans. Regardless of the part of the size spectrum singled out for study 

 the direct measurement of motion requires that a portion of the sea be tagged 

 in order that changes in position with time be measurable. 



The measurement of water motion has been accomplished by a variety of 

 techniques. The measurement of currents using mechanical devices is discussed 

 elsewhere in this volume, see, for example Chapters 13 and 14. Measurements 

 with current meters, the GEK, drogues and buoys provide information con- 

 cerning speed and direction of water motion, but little or no information on 

 the turbulent mixing processes in the sea. The latter has been obtained by 

 measuring the distribution of a variety of chemical substances, both those 

 naturally produced and those introduced by man. 



The measurement of natural and artificial radioactivity is discussed in 

 Chapters 3 and 4 of this volume. Many of the problems connected with the use 

 of artificial radioactive tracers in circulation studies have been discussed by 

 Folsom and Vine (1957). 



The recent developments of fluorimetric techniques for the measurement of 

 the concentration of certain kinds of artificially introduced tags offer the 

 possibility of conducting diffusion or turbulent-mixing studies on a time and 

 size scale not practical by other methods. 



An ideal tag for diffusion studies should have the following properties : 



(a) Its physical, chemical and biological behavior should be identical with 

 that of water. It is, after all, primarily water that is to be followed. 



(b) It should be amenable to quantitative measurement over an extremely 

 wide range of dilution, and the measuring techniques should be adaptable to in 

 situ procedures. 



(c) The cost, ease of handling, and toxicity to both the experimenter and 

 naturally occurring marine organisms should limit neither the size nor number 

 of experiments that can be conducted. 



The fluorimetric technique mentioned above was originally developed for 

 use in turbid, near-shore and estuarine waters. Pritchard and Carpenter (1960) 

 described the results of several experiments in which advection and turbulent 

 mixing were studied. 



Th*e usefulness of the new fluorimetric technique comes from a very fortunate 

 combination of the properties of a commercially available dye, the nature of 

 naturally occurring fluorescent substances and the availability of a fluorimeter 

 with characteristics that make it well suited to in situ measurements. 



Rhodamine B is a dye commercially available in ton quantities (E. T. du 

 Pont). It is normally produced in acetic acid solution which can be adjusted 

 with methanol to in situ density. It shows maximum absorption at 550 mjo. 

 (fluorescence is strongly excited by the 546 m[x mercury line) and maximum 

 fluorescence at 575 mjx. It is biologically inert and is not absorbed to any 



