WATER MASSES AND CURRENTS OF THE OCEANS 157 



within which sinking of surface water to greater depths takes place in 

 winter. In these regions the temperature and the saUnity of the surface 

 water decrease with increasing latitude, and the density increases. The 

 sinking of surface water in these areas therefore leads to the formation 

 of water masses whose temperature-salinity curves reflect the tempera- 

 ture-salinity relations at the surface in the coldest season, as shown 

 schematically in fig. 21, p. 90. Because of the process of formation the 

 character of the Central Water Masses in the different oceans depends 

 upon the temperature and the salinity in the regions of the Subtropical 

 Convergences. 



In adjacent seas that are more or less closed off from the ocean by 

 submarine ridges, special types of water are formed. Thus, in the 

 Norwegian Sea, a deep water is formed by processes similar to those that 

 lead to formation of the Atlantic Deep Water. In the western part of the 

 Norwegian Sea, off the east coast of Greenland, a mixture of the warm 

 Atlantic water that enters the Norwegian Sea to the north of Scotland 

 and the cold water of the East Greenland Current is cooled in winter, and, 

 by vertical convection currents, deep water is formed of temperature 

 -0.8° to -1.2° and of salinity 34.89 to 34.927oo. The upper layers of 

 this water flow into the Polar Sea across the submarine ridge between 

 Greenland and Spitsbergen and fill the Polar Basin. 



In the Mediterranean Sea, evaporation and winter cooling lead to the 

 formation of a deep water of temperature 13.0° to 13.6° and of salinity 

 38.4°/oo to 38.7°/oo. This Mediterranean Water flows along the bottom 

 of the Strait of Gibraltar into the Atlantic Ocean, where it mixes with 

 the Atlantic water and spreads between the surfaces ct = 27.5 and 

 (Tt = 27.7 — that is, below the Antarctic Intermediate Water. It can be 

 clearly recognized over wade areas by an intermediate salinity maximum ; 

 in the South Atlantic, it can be traced around the Cape of Good Hope. 



In the Red Sea a similar but warmer and more saline deep water is 

 formed, having a temperature of 21.5° to 22° and a salinity of 40.5°/oo to 

 41°/oo- This Red Sea Water flows along the bottom of the Strait of 

 Bab-el-Mandeb into the Indian Ocean, where it mixes with other water 

 masses and spreads. The quantities of Red Sea Water entering the 

 Indian Ocean are much smaller than the quantities of Mediterranean 

 Water entering the Atlantic Ocean, and therefore the Red Sea Water 

 exercises a smaller influence. 



Other important water masses in the oceans are formed not by sinking 

 of surface water but by processes of subsurface mixing. The greatest of all 

 is the Antarctic Circumpolar Water Mass, which is mainly formed by 

 mixing of Atlantic deep water and Antarctic bottom water, but also con- 

 tains some Antarctic Intermediate Water and traces of Mediterranean 

 Water. The processes that lead to the formation of this water mass are 

 discussed on pp. 214 and 215. 



