SEA FLOOR STUDIES 



Water Currents on the Sea Floor 



Water current measurements on the sea floor have 

 been made by direct observation from the bathyscaph 

 TRIESTE. Electromechanical devices were not used to 

 sense horizontal current and direction during the period of 

 this report. However, rather accurate measurements of 

 low velocities can be easily made using the bathyscaph. 

 Suspended particles illuminated by the strong external 

 light source of the bathyscaph can be readily seen by the 

 strong Tyndall effect. When the craft is oriented at right 

 angles to the prevailing current, these suspended particles 

 serve as reference points that drift along with the current. 

 A simple determination of velocity is made by measuring 

 the time required for the particles to traverse a 10- cm 

 path, the internal diameter of the window. Current vel- 

 ocities below 10 cm per second are easily measured. 



Observations off San Diego at depths of 700 to 1000 

 feet revealed conditions to be highly variable from dive to 

 dive. On Dive No. 52, current velocity was found to be 

 between 3. 3 cm per second and 5 cm per second (0. 06 and 

 0. 1 knot respectively). On Dive No. 56 at approximately 

 the same location, the current was estimated from motion- 

 picture records to be approximately 0. 5 knot. This rela- 

 tively high-speed current had produced 6- to 8- inch scour 

 holes around scrap-iron tubing 4 inches in diameter that 

 was resting on the sea floor. At this time, the bathyscaph 

 rolled gently from side to side while resting on the sea 

 floor, a characteristic never experienced before. Sea 

 pens, 8 to 10 inches long, that normally stand erect were 

 bent over to within 3 inches of the bottom. There was 

 also an indication of ripple- mark formation and suspended 

 particles were flowing rapidly past. The water mass 

 above the sea floor was turbid from the suspended sedi- 

 ment, and visibility was limited to 2 5 to 30 feet. Hermit 

 crabs in shells 0. 5 to 0. 75 inch in size were tumbled 

 along the bottom, unable to gain footing for more than an 

 instant. The swimming actions of sablefish were recorded 

 as the animal swam "upstream. " During this dive, the 

 operator took advantage of the water currents to carry the 

 bathyscaph across the sea floor. 



K. V. Mackenzie (personal communication) observed 

 similar current velocities in the San Diego Trough (Dive 



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