84 DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



bottom water, but on some parts of the continental shelf surrounding 

 Antarctica rapid freezing in winter produces homogeneous water that 

 attains a higher density than the water off the shelf, and therefore flows 

 down the continental slope to the greatest depths. When sinking, the 

 water is mixed with circumpolar water of somewhat higher temperature 

 and salinity, and therefore the resulting bottom water has a temperature 

 slightly above freezing point (p. 155). An active production of bottom 

 water takes place to the south of the Atlantic Ocean, but not within the 

 Antarctic part of the Pacific Ocean. 



In some isolated adj acent seas the evaporation may be so intense that 

 a moderate cooling leads to the formation of bottom water. This is the 

 case in the Mediterranean Sea and the Red Sea, and to some extent in the 

 inner part of the Gulf of California, in which the bottom water has a high 

 temperature and a high salinity and is formed by winter cooling of water 

 whose salinity has been increased greatly by evaporation. Where such 

 adjacent seas are in communication with the open oceans, deep water 

 flows out over the sill, mixes with the water masses of the ocean, and 

 spreads out at an intermediate depth corresponding to its density 

 (p. 157). 



In general, the water of the greatest density is formed in high latitudes^ 

 and, because this water sinks and fills all ocean basins, the deep and 

 bottom water of all oceans is cold. Only in a few isolated basins in 

 middle latitudes is relatively warm deep and bottom water encountered. 

 When spreading out from the regions of formation the bottom water 

 receives small amounts of heat from the interior of the earth, but this 

 heat is carried away by eddy conduction and currents, and its effect 

 on the temperature distribution is imperceptible. 



Sinking of surface water is not limited to regions in which water of 

 particularly high density is formed, but occurs also wherever converging 

 currents (convergences) are present, the sinking water spreading at inter- 

 mediate depths according to its density. In general, the density of the 

 upper layers increases from the Tropics toward the poles, and water that 

 sinks at a convergence in middle latitudes therefore spreads at a lesser 

 depth than water that sinks at a convergence in high latitudes. 



The most conspicuous convergence is the Antarctic Convergence, 

 which can be traced all around the Antarctic continent (p. 155). The 

 water that sinks at this convergence has a low salinity, but it also has a 

 low temperature and consequently a relatively high density. This 

 water, the Antarctic Intermediate Water, spreads directly over the deep 

 water and is present in all southern oceans at depths between 1200 and 

 800 m. The corresponding Arctic Convergence is poorly developed in 

 the North Atlantic Ocean, where an Atlantic Arctic Intermediate Water is 

 practically lacking, but it is found in the North Pacific, where Pacific 

 Arctic Intermediate Water is typically present. 



