observation) is also the level of minimum temperature. In 

 the example of figure 14, the transparency decreases 

 {dTr/dZ is negative) in the upper 15 feet and reaches a mini- 

 naum {dTr I dZ-0) close to the level of maximum temperature 

 gradient. 



Figure 14. Comparison of vertical temperature and 

 transparency gradients 12 30-1500 on 5 August 1960 

 showing a negative maximum transparency gradient 

 Delow the thermocline. 



SHORT -PERIOD CHANGES IN TURBIDITY 



Visual 



Water turbidity is often visually apparent from the dis- 

 coloration of the sea surface. The most conspicuous dis- 

 coloration in this area occurs periodically during the summer 

 months, when the surface water has a reddish appearance. 

 The phenonaenon is called "red water, " and is principally 

 csMsedhy G-onyau lax polyedra, a very small, one-celled, 

 plant-like organism. Another dinoflagellate, G-ymnodinium 

 flavum, was conspicuous in 1961, and gave an orange cast 

 to the water. Water transparency is greatly reduced during 

 a plankton bloom. 



