Page 583 radio acoustic ranging 633 



be of assistance in determining how frequently serial temperatures should be obtained. 

 Such data have been published for the Atlantic Ocean from Cape Cod to Chesapeake 

 Bay ^ and for the Gulf of Maine. ^ An extensive study of the temperature of the water 

 in Monterey Bay, California ^ has also been published. 



For economic reasons serial temperatures are frequentlj^- observed at night, and 

 when R.A.R. surveys have to be discontinued because of heavy static. A hydrographer 

 should take advantage of every opportunity to obtain serial temperatures and, if prac- 

 ticable, without interfering with other survej'" operations. Using the bathythermograph 

 a serial temperature may be observed while weighing a buoy or while taking a vertical 

 wire sounding. The Bourdon-type bathythermograph (see 4732) can be used from the 

 ship underway, for the temperatures of the upper layers, without delaying other hj^dro- 

 graphic operations. Serial temperatures outside the limits of the survey area, observed 

 at night after anchoring or in the mornuig before getting underway, are generally of 

 little value, for such temperatures will seldom be representative of the area being 

 surveyed. 



633, Salinity of Sea Water 



The composition of sea water is as complicated as the composition of the land, for 

 it is obvious that every soluble substance on land will eventually be carried to the sea. 

 In addition to the salts soluble in water, rain water in passing through the atmosphere 

 absorbs acids. This enables it to dissolve the minerals of the earth into soluble com- 

 pounds and carry them to the sea where they either remain in solution or form insoluble 

 compounds which sink to the sea bottom. Sea water is, therefore, a dilute solution of 

 a number of salt compounds which are strong electrolytes. 



For the sake of simplicity the total amount of dissolved solids in sea water has 

 been arbitrarily designated as the salinity. Salinity is then defined as the total number 

 of grams of solid material dissolved in 1 kilogram of water; it is expressed in parts per 

 thousand, which is written °/oo. The amount of solids may also be expressed in terms 

 of chlorinity, which is defined as the total amount of chlorine present in 1 kilogram of 

 sea water. A constant relationsliip has been found to exist between salinity and 

 chlorinity, expressed by the equation 



Salinity ^0.03 + 1 .805 X chlorinity. 



Salinity is, therefore, just another form for expressing chlorinity, but it is only indirectly 

 related to the total true salt content, with which it is often confused. Oceanographers 

 prefer the use of the term chlorinity in describing the nature of the water, but the Coast 

 and Geodetic Survey uses the term salinity exclusively. When the titration method is 

 used the equipment is calibrated to give the results in terms of salinity. This is de- 

 sirable because the velocity of sound tables have been prepared in terms of salinity. 



Average sea water contains about 35 7oo of solids in solution, of which sodium 

 chloride (27.2 °/oo) and magnesium cliloride (3.8 °/oo) are two of the principal constituents; 

 but there are many other salt compounds in the form of bromides, fluorides, iodides, and 

 carbonates — some in such small proportions as to be negligible in quantitative chemi- 

 cal analysis. Some compounds are absorbed by marine animals, plants, and organisms 



1 Woods Hole Oceanographic Institution, Volume II, No. 4, Studies of the Waters of the Continental Shelf, Cape Cod to Chesa- 

 peake Bay, Part I, The Cycle of Temperature. 



2 Bureau of Fisheries Document No. 969, Physical Oceanography of the Gulf of Maine. 



3 Transactions of the American Philosophical Society, New Series— Volume XXIX, Hydrography of Monterey Bay, California, 

 Thermal Conditions, 1929-1933. 



