to surface waves and internal waves. The hydrophotometer 

 reading will likewise change considerably, and it is not 

 possible to ascribe a very reliable light transmission read- 

 ing to any particular sample. The readings on the hydro- 

 photometer are a function of particulate matter (including 

 plankton) and air bubbles suspended in the measuring path 

 of the light beam, but there are no functional expressions 

 available describing this relationship. The hydrophotom- 

 eter readings were recorded when available. However, 

 these measurements are to be regarded purely in the nature 

 of qualitative information about the general nature of the 

 in situ conditions of the region being sampled. 



As mentioned earlier, the greatest emphasis in the 

 analysis is placed on the dependence of attenuation on the 

 plankton count and oxygen content as measured from the 

 sample. 



EXPERIMENTAL PROCEDURE 



Sampling Methods 



Surface samples were at first obtained by using a 

 bucket at the end of a line. Deeper water was obtained by 

 using standard Nansen bottles. However, it soon became 

 clear that either method was highly unsatisfactory. It was 

 almost impossible to fill a cavity from the bucket without 

 working a large amount of air bubbles into the water, and 

 it was very slow and cumbersome to obtain enough water 

 with Nansen bottles. 



A small submersible centrifugal pump was then pro- 

 cured and mounted on the cart carrying the hydrophotom- 

 eter. A hose carried the water up to the main deck 

 where the cavities were. The pressure in the discharge 

 line from the pump was approximately 12 psi higher than 

 the hydrostatic pressure at the level from which the sample 

 was taken. Cavitation was therefore not likely to occur. 



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