76 



bulletin: museum op comparative zoology. 



In the northerly end of the profile Station 1 is introduced, to show 

 how the cold salt bottom water wells up close to the shore. However, 

 as^pointed out in the discussion of temperatures, this phenomenon is 



Fig. 33. — Salinity profile across Massachusetts Bay, August 13 (Stations 

 44, 45, 46). 



sporadic, probably the result of offshore winds driving the surface 

 water away from the coast, their place being taken by water from 

 below. Conditions at Station 1 show that the effect may be felt to 

 as great a depth as 20 fathoms. 



Density. 



The three features of sea water most interesting to the oceanog- 

 rapher are temperature, salinity, and density; the former because 

 of its biological importance; the second because it is the only safe 

 clue to the geographic origin of water-masses; and the third because 

 of its importance as determining circulation, both vertical and hori- 

 zontal. The last is a product of the first two and of a third factor, 

 namely pressure. And we must never lose sight of the fact that as it 

 is determined by temperature as well as by salinity, it is a temporary 

 quality, changing as the water becomes colder or warmer. In the 

 accompanying table (p. 141), the densities in situ are calculated from 



