SEA WATER TRANSPARENCY MEASUREMENTS 



Water transparency measurements were made from the 

 USS CACOPAN at fifteen different stations in the antarctic. 

 The transparency measurements were made with the aid of a 

 Secchi disk (a white disk 30 centimeters in diameter). The 

 Secchi disk was lowered into the water in a horizontal position 

 and the maximum depth at which the disk was still visible 

 was noted. This depth was taken as a measure of the trans- 

 parency. 



In the Antarctic Ocean the Secchi disk readings (table 10) 

 vary from 23 to 90 feet with an average of 50 feet. Most of 

 the measurements are similar to the average transparencies 

 for open-sea conditions. But the readings between 23 and 

 32 feet at four of the stations are very low transparencies for 

 open-sea conditions. The low transparency is probably related 

 to high phytoplankton production. 



Both the color of the sea and the surface temperature 

 were noted at the same time that the transparency measure- 

 ment was made (see table 10). Antarctic water is typically 

 blue-gray, blue-green, or green. Near the pack ice the water 

 is usually green and of low transparency owing to high organic 

 content. On 19 February a tongue of bright blue water was 

 encountered which appeared to be a tongue of Indian Ocean 

 water that extended into the antarctic. 



ANTARCTIC "SEEING" 



Especially impressive during Operation KIGKJUMP was 

 the crystal clearness of some of the antarctic days, the 

 stellar brilliance of some of the nights, and the consequent 

 fitness of these regions for making celestial observations 

 even from sea-level elevation. 



Polar regions are noted for many curious optical phenom- 

 ena, most of which are related to excellent visibility rather 

 than to optical distortion. It is well known that, because of 

 atmospheric clarity, the mariner and the explorer in high 

 latitudes frequently underestimate distances by as much as 

 50 miles and occasionally by as much as 200 or 300 miles 

 when superior mirages or loomings are involved. Regarding 

 celestial observations, Byrd 5 states that observers at Little 

 America noted as many as 60 meteors per minute. He attri- 

 butes such exceptionally high counts to the clarity of the sky 

 which permitted the sighting of faint trails that would be 

 invisible in other parts of the world. 



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