reasonably adequate to permit good photography and clear 

 observations. On Dive 56 (in Loma Sea Valley) an appre- 

 ciable flow of sediments immediately adjacent to the 

 bottom was noted. A relatively strong current was present 

 of approximately 5 centimeters per second. This flow was 

 adequate to tumble shells inhabited by hermit crabs along 

 the bottom; fishes were noted to swim "upstream"; sea 

 pens, normally rigid and vertical, were swept over to an 

 angle of approximately 45 degrees. 



In the Mediterranean, clouds of suspended matter 

 passed through the illuminated area as the bathyscaph 

 remained in a fixed position. These were probably gener- 

 ated by fishes grubbing in the sea floor sediments. On two 

 occasions, fishes were observed to stir up the sediment 

 apparently in search of food, such suspended clouds were 

 noted to drift in a fixed direction at 1 centimeter per sec- 

 ond. 



Daylight Penetration 



Visual observations from the bathyscaph TRIESTE 

 indicate that daylight penetration down to 600 meters 

 (maximum) can be expected in clear ocean water. 

 Table 3 compares these results with those obtained 

 by other investigators either through direct observation 

 or by the use of cable-lowered bathyphotometers. 



Reasons for the extinction of daylight at 600 meters or 

 less during bathyscaph dives are supplied by Clarke and 

 James'''^ who conclude from their examinations that ocean 

 waters contain suspensoid and filter- passing materials 

 that are effective in increasing absorption, so that sea 

 water is always less clear than pure distilled water. Such 

 suspensoids have been almost invariably observed above 

 and below the depth of daylight penetration on each bathy- 

 scaph dive. 



During 1957, Jerlov and Piccard''"* descended 600 

 meters in the Mediterranean with the TRIESTE for the 

 purpose of measuring daylight penetration. Unfortunately, 

 malfunctions of the photometric equipment made it impos- 

 sible to obtain light- level readings to the maximum depth 

 obtained. This dive represented the only specific attempt 

 with the bathyscaph to obtain photometric readings con- 

 currently with visual observations of daylight extinction. 



43 



