116 THE OCEAN 



decrease of temperature down to at least 

 800 fathoms, but at depths of 1500 fathoms 

 and deeper the increasing density is due both 

 to the slowly diminishing temperature and 

 to the actual increase of the salinity at these 

 great depths. It cannot be doubted that 

 the increased salinity at these greater depths, 

 where the differences of temperature with 

 depth are very small, indicates that the deep 

 waters over the bed of the ocean are derived 

 chiefly from the Antarctic and sub-Antarctic 

 regions, and in a less degree from the Arctic 

 and sub- Arctic regions of the globe. 



When we consider the density in situ in 

 the different oceans, it becomes evident that 

 density has a most important effect on ocean 

 circulation. The mere fact that sea-water 

 is not equally heavy everywhere must be 

 regarded as one of the chief causes of ocean 

 currents. Water being so remarkably mobile, 

 small differences in density result in sensible 

 motion. 



Density at various Depths, — At a depth of 

 100 fathoms there is a marked difference in 

 the density of the water in the North and 

 South Pacific, the density being much higher 

 in the western South Pacific than in the North 

 Pacific. In the eastern South Pacific towards 

 the South American coast the density is low, 

 and here in consequence of the south-east 



