82 



what the navigator needs to know. 



The need of bettering present knowledge of the major currents is 

 fully appreciated by the Hydrographic Services of the seafaring 

 nations. For this reason the United States Hydrographic Office, the 

 British Admiralty, and the German Marine Observatory are continually 

 accumulating a vast aj:nount of data from vessels' log books, as well 

 as from all other available sources, in the hope of improving their 

 yearly and monthly current charts. This, of course, is most important 

 for the regions where the direction of the dominant drift reverses 

 from season to season, as in parts of the Indian Ocean; or which fall 

 within the sweep of a great current at one season, but not at another; 

 or over which the daily velocity varies greatly from season to season 

 with varying winds. 



In certain regions, especially along the west coast of (Africa, 

 rapid advances in knowledge of the currents have been gained within 

 the last few years. But to illustrate the urgent need of still 

 further improvements in more travelled seas, we need only instance 

 the pres-.-nt vaguiness of our understanding of the secular variations 

 in the geographic location of the inner edge of the Gulf Stream drift 

 off the .-ast coast of North Ame^rica, and of the eddying movements plus 

 counter drifts that confuse the orderly procession of that body of 

 tropic water toward the northeast. That the Gulf Stream has shifted 

 its position is a frequent report; one, too, that includes more than a 

 grain of truth. 



Knowledge of the southerly drift along the west coast of North 

 America is still vague. Mor- detailed information is made especially 

 urgent there for th; sake of safety at sea by the scarcity of good 

 harbors of refuge along the coasts of Oregon and California. And 

 "sketchy" fairly describes our present picture of the currents among 

 the Polynesian, Philippine ?nd Malayan Archipelagoes, to mention only 

 striking instances. 



Ocean currents affect navigation indirectly as w:ll a directly, 

 and in a disastrous way, by bringing icebergs and field ice down from 

 the Artie, a frequent menace to the shipping lanes between America and 

 Europe. This menance the maritime nations now meet in part by main- 

 taining the International Ice Patrol, during the danger season, in the 

 region of the Grand Banks, where the steamer routes between the United 

 States and Northern Europe touch the principal lane followed by the 

 bergs in their drift southward from Eavis Straits. But betterment of 

 the Patrol demands more detailed examination of the variations in the 

 two great currents (Labrador and Gulf Stream) that meet there, the 

 first bringing the bergs, the latter melting them. To gain a better 

 understanding of the factors that control the journeying of the bergs, 

 the Patrol has recently expanded its activities to include a dynamic 

 survey of the whole region between Labrador and Gr;cnland, as described 

 in another section (page ). And should the Patrol be extended to 

 include the more northern routes it will become increasingly important 

 to m.ake periodic surveys of these northern waters in the hope of ex- 

 plaining, and perhaps predicting the wide variations in the amount of 

 iCe that comes southward from year to year, and the varying tracks 

 that the bergs follow. 



As demands grow for an extension of maritime trade routes more 



