WATER MASSES AND CURRENTS OF THE OCEANS 21 1 



the direction of flow (p. 121), because the current is continuous around 

 the earth, and therefore it must be balanced by other frictional stresses. 

 The velocities along the bottom are too small to give rise to bottom 

 friction, and one is therefore led to the conclusion that great stresses due 

 to lateral mixing exist at the boundaries of the current. The torque 

 exerted by these stresses along the quasi-vertical boundary surfaces of 

 the current must balance the torque exerted by the wind on the surface, 

 but so far no attempt has been made at an analysis of the dynamics of 

 the current, taking friction into account. 



The Deep-Water Circulation of the Oceans 



The manner in which the deep and bottom water is formed has been 

 discussed (p. 155) and certain statements as to the deep-water circulation 

 have been made, but so far no general review of the deep-water circu- 

 lation has been presented. Table 22 has been prepared in order to 

 facilitate such a review. It contains temperatures, salinities, and oxygen 

 values of the deep and bottom water at fifteen selected stations, six in 

 the Atlantic, three in the Indian, and six in the Pacific Ocean, including 

 the adjacent parts of the Antarctic Ocean. The oxygen content of the 

 water has not been discussed, but is included here because it is useful 

 when examining the slow spreading of deep water. The content is 

 generally high near the sea surface, where oxygen is absorbed from the 

 air, but low in '^old" deep and bottom water, in which oxygen has been 

 used up by respiration of marine organisms or for decomposition of 

 organic remains. The content of table 22 will not be dealt with sepa- 

 rately but must be examined as the discussion proceeds. 



In order to understand the deep-water circulation, one has to bear 

 in mind that deep and bottom waters represent water whose density 

 became greatly increased when the water was in contact with the atmos- 

 phere, and that this water, by sinking and subsequent spreading, fills 

 all deeper portions of the oceans. The most conspicuous formation of 

 water of high density takes place in the subarctic and in the antarctic 

 regions of the Atlantic Ocean. The deep and bottom water in all oceans 

 is derived mainly from these two sources, but is to some extent modified 

 by addition of high-salinity water flowing out across the sills of basins 

 in lower latitudes, particularly from the Mediterranean and the Red Sea. 



In the North Atlantic Ocean, North Atlantic Deep and Bottom 

 Waters flow to the south, the flow being reinforced, and the upper deep 

 water being modified, by the high-salinity water flowing out through the 

 Strait of Gibraltar. The newly formed deep and bottom water has a high 

 oxygen content that decreases in the direction of flow. Fig. 60 and the 

 values given in table 22 demonstrate the character of these waters and 

 show particularly the increase in salinity at moderate depth that is due 

 to addition of Mediterranean water. Antarctic Bottom Water flows in 



