AEROGRAPHER'S MATE 3 & 2 



The Equatorial Water mass is also found in 

 the northern part of the Indian Ocean, In this 

 case, the higher salinities of Equatorial Water 

 are probably due to mixing with Red Sea 

 water; however, this conclusion has not been 

 definitely established. 



The Central and Equatorial Water masses 

 are usually not discernible at the surface, but 

 are covered by a surface layer of 100 to 200 

 meters in thickness. In this surface layer, the 

 temperature and salinity of the water indicate 

 wide variations from one area to another, 

 depending on variations in current structure, 

 evaporation, precipitation, and various seasonal 

 changes, especially in the middle latitudes. This 

 surface layer of warm water is separated from 

 deeper water by a transition layer within which 

 the temperature decreases rapidly with depth, 



Subantarctic and Subarctic 

 Water Masses 



Subantarctic Water occurs between the Cen- 

 tral Water masses of the southern oceans and 

 the Antarctic Convergence. The physical 

 properties of this water mass are quite con- 

 servative and extend completely around the 

 earth, Subantarctic Water is considered to belong 

 to the waters of the Antarctic Ocean. This water 

 is of relatively low salinity and is probably 

 formed by a combination of mixing and vertical 

 circulation in the region between the Subtropical 

 and Antarctic Convergences, The corresponding 

 Subarctic Water of the North Atlantic is not 

 nearly as extensive as that of the Subantarctic 

 Water of the South Atlantic. It covers only a 

 small area and is found to have a higher salinity 

 than the surrounding water. However, in the 

 North Pacific the corresponding Subarctic Water 

 covers a wide area and is of lower salinity 

 than the surrounding water. 



The variations between the Subarctic Water 

 and the Subantarctic Water masses indicate 

 that they must be formed by different processes. 

 In the southern oceans the Antarctic Conver- 

 gence presents a continuous and well-defined 

 boundary, whereas in the northern oceans the 

 corresponding Arctic Convergence is found only 

 in the western portions of the oceans. In some 

 areas there exists no well-defined northern 

 boundary to the Subarctic Water. The differences 

 between the water masses of the northern and 

 southern oceans are reflections of the differences 

 in the character of the land and sea distribution. 



Although Subarctic Water is similar to Arctic 

 Intermediate Water, Subantarctic Water differs 

 distinctly from Antarctic Intermediate Water. 



Intermediate Water Masses 



Intermediate Water masses are found below 

 Central Water masses in all oceans. The 

 Antarctic Intermediate Water is the most wide- 

 spread. Intermediate Water differs from Central 

 Water in that it sinks along a well-defined line. 

 It does not form as a WATER MASS at the 

 surface and then sink. Instead, it forms from 

 the sinking of a WATER TYPE (see definitions 

 at the beginning of this chapter) with a salinity 

 of 33,8 7oo and a temperature of 2,2° C which 

 encircles the Antarctic Continent and mixes with 

 the waters above and below. This mixing 

 gradually develops into a water mass. One of 

 the characteristics of the Intermediate Water 

 mass is a salinity minimum when compared 

 with the surrounding water. Since the Equatorial 

 Water does not exist to form a boundary 

 between the north and south in the Atlantic 

 Ocean, the salinity minimum of the Antarctic 

 Intermediate Water extends across the Equator 

 to about 20° to 35°N latitude. In the South 

 Pacific and Indian Oceans where Equatorial 

 Water exists, the Antarctic Intermediate Water 

 spreads northward to around 10°S latitude. 



Arctic Intermediate Water forms in small 

 quantities east of the Grand Banks of New- 

 foundland in a small area of the northwest 

 Atlantic, 



The Arctic Intermediate Water of the North 

 Pacific lies between latitude 20° and 43°N 

 except off the North American west coast where 

 Subarctic Water flows farther southward. 

 Arctic Intermediate Water of the North Pacific 

 is formed during the winter at the convergence 

 formed by the Oyashio Current and the Kuro- 

 shio Extension. The Oyashio is a cold, southerly 

 moving current (described earlier in this 

 chapter) that converges with the warm, 

 northeasterly moving waters of the Kuroshio 

 at a latitude of about 40 °N and a longitude around 

 160°E. 



There are two other Intermediate Water 

 masses likely to be encountered by the A.ci^" 

 rapher's Mate in his studies of Oceanography. 

 These are those formed in the Atlantic and 

 Indian Oceans as a result of the interactions 

 of Mediterranean Water in the Atlantic and 

 Red Sea. Water in the Indian Ocean, The 



394 



