light transmission (31 percent) recorded during the period 

 closely approximated the high point of the oscillation. This 

 long-period disturbance was believed responsible for the 

 appearance of G. polyedra at the surface and indicates again 

 the role played by thermal density stratification in the dis- 

 tribution of microorganisms. Scuba observers estimated 

 underwater visibility to be 5 feet in the most turbid area. 

 Visibility increased to 20 feet at a depth of 15 feet. Deeper 

 water showed visibility of approximately 40 feet. These 

 observations correlated closely with hydrophotometer data. 

 The passage of this red-water patch was observed from the 

 bottom by a diver who likened its approach to that of a line 

 squall. While near-bottom water was clear^ diver activity 

 under a front of this type would be hampered by the reduc- 

 tion in light from the surface. 



Figure 32 illustrates the rapid change in transparency 

 during the passage of red water. It is believed that the 

 23-percent reduction in transparency was caused entirely 

 by the passage of red water. 



On 24 July the transparency and temperature data 

 (figs. 33 and 34) suggest a large patch of red water, at sub- 

 surface depths, which reached the measurement site at 

 approximately 0905. This conjecture is consistent with 

 the presence of a thicker thermocline and therefore a more 

 gently sloping density barrier within which the organisms 

 would be dispersed more evenly. The presence of red water 

 below the surface is commonly revealed in the wake of a 

 ship when the organisms are churned to the surface by the 

 propeller. The surface red water around the tower at 1042 

 (fig. 33) probably represented a short-term divergence not 

 apparent when temperature was taken at relatively long 

 intervals. 



62 



