Pacific in the diving into the Marianas Trench. Echo 

 sounding does not show the configuration of the floor along 

 the axis of these trenches because of the broad-beam of 

 the sounders, the depth of water, and side echoes. As a 

 result of the TRIESTE program, it is now known that the 

 trench (and probably others) has a wide flat floor; that 

 currents are not active in it (at least not continuously); 

 and that it has little benthic animal activity. Furthermore, 

 the nature of sediment in the trench was ascertained. The 

 sediment of the trench previously was known from only one 

 small sample taken by the HMS CHALLENGER in 1952, 

 and in another portion of the Trench. 



4. Other conclusions are: 



a. Particulate matter exists to some degree to 

 all depths in the oceans. 



b. Water clarity in the deep oceans generally 

 permits observation from the bathyscaph to distances up 

 to 60 feet, when lighting conditions are suitable. A new 

 arc for in situ observations on "visual oceanography" is 

 indicated. 



c. For the bathyscaph observer, extinction of 

 daylight in the ocean generally occurs at approximately 

 600 meters. 



d. At depths of over 2100 meters, biolumines- 

 cence was observed only as single, or small groups of 

 flashes. Upon ascending to 700 meters, the number of 

 flashes increased rapidly as much as 1000 times. At 

 shallower depths bioluminescence remained high until 

 "washed out" by daylight. 



57 



