Ocean Currents 



A 39 



neighborhood a series of observations by 

 Admiral Irminger, of the Danish navy, 

 showed that the westerly drift of the 

 water could still be detected at a depth 

 of 900 meters. 



A striking instance of the fluctuations 

 of the surface currents with the winds 

 is shown in the case of the straits sepa- 

 rating the Greater Antilles, the Wind- 

 ward, and the Mona passage. From 

 January to April, the months when the 

 northeast trades are most northerly in 

 direction and blow with maximum force, 

 a strong southwesterly set is felt upon 

 entering these passages. As the season 

 advances and the trades weaken, at the 

 same time becomingsoutheasterly , these 

 currents diminish and change their di- 

 rection to northwest. 



Throughout the entire extent of the 

 Caribbean Sea the drift is westerly, save 

 that in those portions where resistance 

 to the flow is offered, such as the southern 

 coast of Cuba, return currents manifest 

 themselves. Throughout the Yucatan 

 passage the drift is northwesterly, but 

 here again the influence of the return 

 current is felt, notably under Cape San 

 Antonio, the western extremity of Cuba, 

 where southeasterly sets are frequent. 

 In the Gulf of Mexico observations 

 have thus far failed to reveal an)' de- 

 cided set of the surface water. 



THE GULF STREAM 



Between the northern coast of Cuba 

 and the Florida reefs starts the most 

 celebrated of all ocean currents, the 

 Gulf Stream. Discovered by Ponce de 

 Leon in 15 13, it has from that time 

 been and still is the subject of scientific 

 investigation. 



In the Gulf Stream we have to deal 

 with a current of a nature entirely 

 distinct from those which we have thus 

 far considered. These were all due to 

 the direct action of the wind upon the 

 water, producing a drift. The Gulf 

 Stream is only indirectly due to this 



cause, being the overflow of the water 

 heaped up by the trade-wind drift in 

 the Caribbean Sea and the Gulf of Mex- 

 ico. Throughout a considerable por- 

 tion of its extent its direction, even at 

 the surface, is independent of the wind 

 or only slightly modified by it. The 

 stream reaches its maximum strength 

 at the point where it emerges from the 

 Bernini Straits between the Bahama 

 bank on the east and the coast of Flor- 

 ida on the west. The breadth of the 

 actual current here between Fowey 

 Rocks and Gun Cay Light js 38 miles, 

 its average depth 239 fathoms, its aver- 

 age velocit) r 50 miles in 24 hours, 

 although it rises at times to 100 miles. 

 Farther north its breadth increases, 

 and its velocity is correspondingly di- 

 minished. The western edge of the 

 stream in its northward course along 

 the coast of the United States follows 

 closely the 100-fathom curve, although 

 the axis of the stream, the line of great- 

 est velocity, lies somewhat further sea- 

 ward, its position varying, according 

 to Pillsbury, with the declination of 

 the moon, lying (at Jupiter) 8 miles 

 farther off shore at time of low moon 

 than at time of high. From Jupiter to 

 Hatteras the axis runs at a distance 

 varying from 11 to 20 miles outside the 

 1 00- fathom curve. 



The color of the stream is a percep- 

 tibly deeper blue than that of the neigh- 

 boring sea, this blueness forming one 

 of the standard references of the nauti- 

 cal novelists. The depth of color is 

 due to the high percentage or salt con- 

 tained, as compared with the cold green 

 water of higher latitudes, observation 

 having shown that the more salt held 

 in solution by sea water the more in- 

 tensely blue is its color. Thus even in 

 extratropical latitudes we sometimes 

 observe water of a beautiful blue color, 

 as for instance in the Mediterranean 

 and in other nearly land-locked basins, 

 where the influx of fresher water being 

 more or less impeded, the percentage of 



