Slicks were noted but once on the high seas during the 

 homeward passage. These slicks, found in a subtropical 

 area (latitude 20°S, longitude 75°W) under unusually calm 

 conditions, were only faintly discernible. However, well- 

 developed slicks were found in Australian coastal waters, 

 and especially striking slicks were seen in the insular waters 

 of American Samoa. And, when the coastal waters of Cali- 

 fornia were reached, prominent slicks were again found. 



Thus it would appear that, under favorable conditions, 

 slicks that are just faintly discernible may be found in oceanic 

 water, but that the most prominently developed slicks are to 

 be found in coastal and insular waters that typically have 

 high organic production. This further suggests that slicks 

 are produced from natural oil of organisms and, conversely, 

 that slicks may have a practical use as indicators of high 

 organic productivity. 



During Operation HIGHJUMP, it was noted that during 

 calm conditions slicks have a patchy distribution but, undef 

 windy conditions, they drift with, or slightly faster than, 

 the surface water and tend to line up in elongated streaks 

 parallel to the wind. Probably the streaks are developed 

 by the slick material collecting along small convergences 

 associated with helical circulating cells of water in the 

 homogeneous layer above the thermocline .42,43 High winds 

 and attendant rough seas result in the complete disappearance 

 of the slick patterns. A critical velocity of only a few miles 

 per hour and no fetch at all is normally required to form 

 capillary ripples, but a considerably higher wind velocity is 

 needed to produce ripples in a slick area. 



Slicks appear as glassy streaks largely because they 

 damp out the small ripples and thus produce a calm area in 

 the midst of rough water. This calming effect appears to be 

 mainly caused by the molecules of the slick film forming a 

 cohesive and nonmiscible blanket over the water so that the 

 slick particles do not take part in the vertically circular 

 motion described by the water molecules when ripples are 

 present. In addition to the damping effect that slicks have 

 upon the water ripples entering a slick patch, the slick sub- 

 stance itself probably resists the formation of capillary 

 ripples because of certain physical properties such as a 

 relatively high viscosity. Also, there must be a considerable 

 frictional drag along the slick-water boundary, and the film 

 is so thin that the vertical circulation necessary to produce 

 capillary ripples with the slick substance cannot be set up. 

 Thus, even a fresh water film such as from melting ice 

 floating on top of cold and saline salt water can produce 

 a slick. But, the fact that slicks are generally surface films 



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