172 The Realm of Nature CHAP. 



New Zealand. In the Southern Ocean there is practically 

 no annual change of temperature, the water growing steadily 

 colder toward the Antarctic ice at all seasons. Toward the 

 north the ocean grows cooler more gradually, 40 being 

 found in summer only in the Arctic Sea, but in winter between 

 New York and the Lofoten Islands, and between Japan and 

 Alaska. As a general rule the sea surface on the west 

 coasts of the southern continents is colder, and on the west 

 coasts of the northern continents warmer, than on the east 

 coasts in the same latitudes ( 241). The northern half of 

 each ocean is also warmer than the southern half at all 

 seasons. Enclosed tropical seas have the highest tempera- 

 ture of any water surfaces in the world. In the Red Sea 

 readings of from 90 to 100 F. have been reported. 



234. Polar Seas. The Arctic Sea, lying in the coldest 

 region of the globe, appears to be frozen over every 

 winter, and the ice, measuring from 2 to I o feet in thickness, 

 is only partially dissipated in summer. Ice first forms 

 along the shore-line, remaining attached to the land as a 

 flat shelf, termed the ice-foot, which is often strewn with 

 boulders and shattered rocks from the cliffs that tower 

 above it. Thence the surface gradually freezes across. 

 When the winter covering of the ocean breaks up, ice- 

 islands, or floes, some of which have been seen 60 miles 

 long, drift away with the wind. Open lanes and wide 

 expanses of water thus appear in summer across the Arctic 

 Sea, but these are liable to be closed at any time by a 

 change of wind driving the floes together. Two floes in 

 collision present a grand and terrifying scene, the ice crack- 

 ing and rending with a noise louder than thunder, while the 

 shattered sheets are piled up one above another to a great 

 height, forming irregular hummocks or ice-hills. Sir George 

 Nares, in the last great North Polar expedition, found the 

 ice-floes in what he called the Palasocrystic Sea more than 

 150 feet thick, and he estimated that some of them were 

 500 years old. The water in which the floes float has the 

 temperature of melting sea ice (about 28), and the lower 

 layers are usually considerably warmer. Indeed, in Polar 

 regions there are often alternate layers of cold and warm 



