156 WATER MASSES AND CURRENTS OF THE OCEANS 



so that a bottom water, the Antarctic Bottom Water, is formed with a 

 saHnity of about 34.66°/oo and a temperature of about —0.4°. This 

 water represents a water type (p. 88), but as it spreads it becomes mixed 

 with adjacent water and attains the character of a water mass, which is 

 marked by a certain temperature-saUnity relation (p. 88). 



North Atlantic Deep and Bottom Water is formed in the Labrador Sea 

 and in the region between Iceland and the southern part of Greenland. 

 There the warm and saline waters of the North Atlantic drift are mixed 

 with the colder and less saline water of the East Greenland Current. In 

 winter, when this mixed water is cooled at the surface, it attains a 

 sufficiently high density (up to o-t = 27.88) to sink. The water that sinks 

 to depths greater than 1000 m has a salinity between 34.90 and 34.96°/oo 

 and a temperature between 2.8° and 3.3° (table 19, p. 170). Variations in 

 the processes of mixing and cooling lead in different years to the sinking 

 of water of somewhat different temperatures, salinities, and densities. 

 The vertical convection currents therefore reach different depths and lead 

 to the formation of a water mass within which the temperature decreases 

 somewhat with depth. Corresponding deep water is not formed in the 

 North Pacific, where no water of high salinity is subjected to intense 

 cooling in winter. 



Antarctic Intermediate Water sinks at the Antarctic Convergence. This 

 convergence, the cause of which is not clearly understood, can be traced 

 all around the Antarctic Continent within the belt of the strong and 

 prevailing westerly winds. The water that sinks at the Convergence is a 

 water type having everywhere a salinity of about 33.8°/oo and a tempera- 

 ture of about 2.2°, the corresponding at being 27.0. After the water 

 leaves the surface, mixing with the over- and underlying bodies of water 

 leads to the formation of a water mass that spreads to the north between 

 the surfaces at = 27.2 and at = 27 A, and at its core is characterized by 

 a salinity minimum. 



North Atlantic Intermediate Water is formed in a similar manner at a 

 convergence to the south of the Labrador Sea, but on a very small scale. 



North Pacific Intermediate Water is similarly formed in the north- 

 eastern part of the North Pacific, in about latitude 40°N, but, when it 

 spreads to the west and south, subsurface water is added in relatively 

 large quantities. The North Pacific Intermediate Water is therefore 

 lacking the characteristics that it would show if it were formed mainly by 

 the sinking of surface water, such as a high content of dissolved oxygen. 

 In contrast to the Antarctic and North Atlantic Intermediate Waters, it is 

 poor in oxygen. 



The Central Water Masses of the different oceans are formed by sinking 

 at the Subtropical Convergences. The Subtropical Convergences are 

 found in all oceans in latitudes 35° to 40° S and 35° to 40°N. They are 

 not well-defined lines of convergence, but represent regions of convergence 



