CHAPTER IX 

 Water Masses and Currents of the Oceans 



Water Masses of the Oceans 



In oceanography the introduction of the concept of water masses 

 has been as fruitful as the introduction of the concept of air masses in 

 meteorology. In the ocean, however, a steady state is more closely 

 approached, and the distribution of the water masses deviates from the 

 distribution of the air masses in that the boundaries between different 

 water masses are always found in approximately the same localities and 

 that the quasi-horizontal boundaries between water masses are as well 

 defined and important as are the inclined boundaries. 



In middle and low latitudes the arrangement of the water masses in a 

 vertical direction is such that one can distinguish between the surface 

 layer, the upper water, the intermediate water, the deep water, and, in 

 some localities, the bottom water. In high latitudes the intermediate 

 water is often lacking, and the upper water is similar to the deep water. 

 In a vertical direction the density of the water increases with depth, and 

 in a horizontal direction the density in general increases toward the polar 

 regions. Surface water of a given density which sinks in higher or middle 

 latitudes spreads along the proper density surface {at surface) ; hence in 

 middle latitudes the vertical distribution of density reflects the horizontal 

 distribution during the season when the surface densities are greatest — 

 that is, during the season when sinking of surface water is most likely to 

 occur. 



The following water masses are formed by sinking of surface water in 

 different localities. Antarctic Bottom Water is formed near the Antarctic 

 Continent, particularly in the Weddell Sea area to the south of the 

 Atlantic Ocean. On the continental shelf the salinity of the water is 

 increased by freezing of ice, so that water is formed at a salinity of about 

 34.62°/oo and a temperature of about —1.9°. Expressed as ct, the 

 density of this water is 27.89, which is higher than the density of the 

 adjacent circumpolar water, for which ct = 27.84, the water having a 

 salinity of 34.68°/oo and a temperature of 0.5°. The water on the 

 continental shelf therefore sinks, flowing down the continental slope, but 

 in sinking it mixes with the warmer and more saline circumpolar water, 



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