OCEANOGEAPHY ISELIN 259 



In order that those unfamiliar with deep-sea oceanographic work 

 may get some idea of the type of problems now being studied, we 

 will describe presently the investigations made by the Atlantis dur- 

 ing the past year. Since these have been largely in the field of 

 physical oceanography it will be necessary first to point out a few 

 of the features of the circulation of the North Atlantic, bearing in 

 mind that, although we will be discussing the North Atlantic, the 

 same jDroblems exist in the other oceans, as they all work in the same 

 manner. Therefore, discoveries in any ocean can usually be applied 

 to the others. In other words, it is not necessary to sail very great 

 distances to do important oceanographic research. 



The current system of the North Atlantic basin, as in the case of 

 the other oceans, is partly convectional in nature and partly wind- 

 driven. Since the water is heated near the equator and cooled in 

 the north, a current system is naturally set up owing to the distribu- 

 tion of density resulting from the thermal inequalities. On the 

 other hand, the evaporation at the sea surface is probably on the 

 whole greater than the precipitation in the southern half of the 

 ocean, and the reverse in the north. Through this cause, the surface 

 water is made relatively heavy in the south and thus the distribu- 

 tion of density due to temperature is partly counteracted and the 

 convectional circulation, much dependent on temperature, some- 

 what retarded. It is thought that the Gulf Stream system is largely 

 a manifestation of this need for thermal transfer from south to 

 north. 



In the southern North Atlantic the water movements are probably 

 dominated by the trade winds which blow the surface waters west- 

 ward towards the islands of the West Indies, so that the water level 

 in the Caribbean Sea and the Gulf of Mexico may be somewhat 

 higher than farther north. At any rate, the result is a swift current 

 through the Straits of Florida and the beginning of the Gulf Stream, 

 which carries some of the warm southern water northward to the 

 Grand Banks and then eastward toward Europe. But the forces 

 which maintain the eastward drift in the northern latitudes are 

 probably only partly convectional in nature, for in these latitudes the 

 prevailing westerly winds undoubtedly exert a strong influence. In 

 this manner a huge clockwise eddy is maintained in the North 

 Atlantic. 



Owing to the fact that the waters of the ocean are usually arranged 

 in stable layers, and that Archiraedlan forces tend to keep these 

 layers horizontal, unless disturbed by some outside force, the char- 

 acter of such a cm-rent as the Gulf Stream is surprising. Through 

 the effect of the earth's rotation the normally horizontal water lay- 

 ers are sloped across the path of any current so that the lighter water 

 149571—33 18 



