THE NAVY OCEAN SCIENCE PROGRAM 19 



soiind-propagation conditions that influence sonar operations 

 can be derived. These descriptions of water masses, however, 

 usually have been limited to average conditions derived from 

 observations of physical and chemical properties obtained over 

 many seasons and years. Large-scale investigations are now 

 being conducted in the North Atlantic and North Pacific Oceans 

 to determine in greater detail the dominant factors influencing 

 both the geographic and temporal variations observed in the 

 water mass and current structure of these oceans. From these 

 studies, second-generation problems for further investigation 

 also are being developed. Such problems concern the mechanisms 

 of water-mass formation and locations in the world in which 

 such formation occurs, the flow of these water masses and the 

 modifications which occur to them during their transit through 

 the oceans, and external environmental conditions which con- 

 tributed to unique events such as the El Nino condition of 

 warm-water penetration southward along the west coast of 

 South America. New techniques, including the use of bio- 

 logical indicators, are also being explored and developed to aid 

 in the tracking of specific water masses and currents for these 

 studies. 



The major current systems are being systematically in- 

 vestigated, in many cases by joint efforts of several groups 

 working on a single current. The emphasis is upon the de- 

 lineation of the general features of both surface currents and sub- 

 surface currents, as well as their variability with time and 

 location. Studies are being conducted to learn more about the 

 Kuroshio current, the equatorial current systems of both the 

 Atlantic and Pacific, and the Yucatan current and its influence 

 upon the waters of the Gulf of Mexico; but the principal object 

 of research on ocean currents is the Gulf Stream system. The 

 research on this system extends from the Straits of Florida to 

 the waters east of Cape Hatteras. A variety of methods are being 

 used to determine its general features and variability. The 

 depth and structure of the flow, as well as the development and 

 persistence of eddies developed from the Stream, are being 

 measured from ships, aircraft, and instrumented buoy systems. 



