lish patterns of movement that can be traced far to sea 

 and possibly may have profound biological effects. These 

 patterns take the form of great circling wheels of water. 

 They appear as a result of the same physical process that 

 causes a flag to flutter in the breeze. The technical name for 

 this phenomenon is the von Karman wake (fig. 18). It is 

 named after Theodore von Karman (1881-1963), the hydro- 

 dynamicist whose studies in 1911-12 led to an understanding 

 of it. Von Karman wakes had not been observed in large- 

 scale flow until the space age began. Then cloud patterns 

 photographed by weather satellites identified them in the 

 atmosphere. 



The water flow to the west of Hawaii at first appeared to 

 be a random system of turbulence, Barkley says. But as 

 data accumulated, a regular pattern of movement was dis- 

 cerned. Like lazy whorls of smoke, eddies form at the 

 northwestern and southwestern tips of Hawaii. The eddy 

 to the northwest rotates counterclockwise, that to the south- 

 west clockwise. As the eddies grow, the main stream rips 

 them from the island tips, like soap bubbles torn from the 

 pipe, and they drift westward. But they maintain their 

 identity as far to sea (500 miles) as the Laboratory's 

 research vessels have attempted to trace them. Usually, one 

 grows more rapidly than the other, so that a large counter- 

 clockwise eddy on the northwest will expand until its dimen- 

 sions are about those of the island, that is, about 60 miles in 

 diameter. Then it drifts aw^ay and a clockwise eddy from the 

 southwest takes its place. The lee of the island can hold a 

 train of these eddies for hundreds of miles to sea. It consists 

 of a stream about 90 miles wide, having a "wavelength" 

 (the distance between successive eddies of the same type) 

 of about 120 miles. The entire train of eddies which make up 

 the wake moves westward about 6 miles a day, or about 75 

 percent of the speed of the current which generates it. 



What this water movement may mean biologically is 

 interesting: The counterclockwise eddies bring cool water 



and nutrients such as phosphate and nitrate for ocean plants 

 up from the depths to near the surface. In the center of the 

 counterclockwise eddy, relatively cool water can be found at 

 a depth of 150 feet or less. Eighty miles away, in the center 

 of a clockwise eddy cool water is more than 600 feet beneath 

 the surface. 



Barkley thinks it takes the eddies about 10 to 15 days to 

 form and move away from the island, which would mean 

 that the western coast of Hawaii would be bathed by waters 

 of different types every 2 weeks during fall and winter, 

 when the eddies have been most often observed. He thinks 

 al.«o that the differences between the northern and southern 

 eddies in such properties as temperature, plant nutrients, 

 and perhaps salinity, might possibly be reflected in the 

 amount of food present for fishes to eat, and thus in fish 

 abundance. 



Although the significance of the large downstream eddies 

 was noted only within the past few months, it had been 

 described as early as 1949, when the research vessel Hugh M. 

 Smith made one of the first oceanographic cruises in Hawai- 

 ian waters. The area has been visited since then, upon 

 occasion, but not enough cruises have been made to deter- 

 mine whether the eddies prevail throughout the year or 

 appear only during the fall and winter. Sometimes the cur- 

 rents from the east may be too weak to set an eddy moving 

 westward from the island. Or the currents may be so strong 

 that they break up the pattern shortly after it forms. 

 Barkley suggests that the total annual productivity of the 

 area may depend upon the number of divergent, cyclonic, 

 counterclockwise eddies that form each year. 



Barkley's principal task at the Laboratory in Honolulu has 

 been the preparation of an oceanographic atlas of the Pacific 

 Ocean, which will be published by the University of Hawaii 

 Press ; in it are summarized all oceanographic observations 

 in the Pacific Ocean from 1917 through 1964. While prepar- 

 ing the charts for the atlas, Barkley recognized that the 



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