78 THE OCEAN 



the open ocean, carrying with it a temperature 

 corresponding to that at the top of the barrier 

 (see Fig. 3). Such is the case in the Sulu Sea, 

 the Banda Sea, etc. 



The deep water of the enclosed basin may 

 take a temperature determined by the mean 

 winter air-temperature of the region, and this 

 deep water then flows as an undercurrent 

 over the barrier into the open ocean, as in the 

 case of the Mediterranean and the Red Sea. 



Another variation in the distribution of 

 temperature occasioned by barriers is found 

 in the case of a polar basin cut off from 

 the general oceanic circulation, such as the 

 Norwegian Sea, cut off from the Atlantic 

 by the Wyville Thomson Ridge, the summit 

 of which is covered by water 200 to 250 fath- 

 oms in depth. Here the warm Atlantic water 

 flows northwards, and the cold water found 

 on the northern side of the ridge is this 

 Atlantic water which has been cooled in the 

 Norwegian Sea, has sunk towards the bottom, 

 and then flowed south as far as the 

 Wyville Thomson Ridge in depths greater 

 than 250 fathoms. The result is that the 

 temperature on both sides of the ridge 

 decreases from surface to bottom, but to the 

 north of the ridge the decrease downwards 

 from the level of the ridge is much greater 

 than to the south (see Fig. 4), so that a differ- 



