The correlation between the sound attenuation and the 

 variables shown in figure 31 is very poor. The attenua- 

 tion goes down from its high daytime value to about 30 

 db/kyd at night, but this value is still significantly higher 

 than the attenuation of pure sea water, and corresponds to 

 the values obtained when a sample was left standing in the 

 cavity. 



This behavior can be understood if it is postulated that 

 the plankton produces oxygen nuclei during the daytime 

 hours only. During the dark period the nuclei disappear 

 either because their stability in time is limited, or perhaps 

 because they are carried to the surface by convection cur- 

 rents where they develop into bubbles and escape. 



96 



