SEA WATER 231 



Atlantic Drift. Still bearing to the right it bathes the 

 coasts of Ireland and then the western coasts of Scotland. 

 Passing the north of Scotland it meets again that portion 

 which had been deflected near the Labrador coasts and the 

 two carry on together to the north of Norway, a small 

 branch turning south into the North Sea. 



On reaching Arctic regions this originally warm surface 

 water has been cooled down nearly to freezing point. 

 It has however still a larger salt content than the water 

 over which it has been flowing, and is therefore heavier 

 at the same temperature. It therefore sinks, and then 

 creeps slowly back towards the equator as a deep bottom 

 current which rises once more just north of the equator 

 to replace the water that is being driven westwards on the 

 surface by the trade winds. 



Such in simple outline are the main features of the 

 oceanic circulation in the North Atlantic. In the South 

 Atlantic a slightly different circulation exists on account 

 of the configuration of the land masses ; and the two 

 systems become linked up in the region of the South and 

 North Equatorial Drifts. 



In the Pacific, too, there is a system of oceanic currents 

 much after the manner of that in the Atlantic, the Japan 

 Current or " Kuro Shi wo " corresponding to our Gulf 

 Stream. 



In these great circulations there are to be distinguished 

 two types of water movement, the " drifts," and the 

 " currents " or " streams." 



The drifts are brought about by wind action, and are 

 horizontal movements of the surface waters more or less 

 in the same direction as the wind is blowing. Currents on 

 the other hand are translocations of bodies of water caused 

 by a definite head of water. In the Gulf of Mexico such a 

 head of water is produced in the manner mentioned above 



