Introduction 



The summaries of sea water densities presented in this publica- 

 tion are based on observations made in Atlantic harbor and coastal wa- 

 ters through the year 1956. The densities were observed primarily at 

 tide stations which, in the United States, were maintained by the Coast 

 and Geodetic Survey, often with the cooperation of other organizations. 

 Final results for places in Venezuela were supplied by the Ministerio 

 de Obras Publicas, Estados Unidos de Venezuela. For other countries , 

 the Coast and Geodetic Survey derived the data from observations made 

 by organizations in the countries concerned. In Latin America the ob- 

 servations were obtained through the cooperation of the Inter American 

 Geodetic Survey. 



Table 1 presents monthly means and annual mean and extremes for 

 each year of observations. Maximum and minimum densities are shown for 

 each year in which observations were made, whether or not the observa- 

 tions covered the whole year. In all cases the yearly extremes are from 

 the months of the year for which means are given. If they are from an 

 incomplete year, they are followed by an asterisk. 



For each station at which the series of observations covered two 

 or more years, there are given also the following monthly values for 

 the series: the mean of the monthly means together with its correspond- 

 ing salinity, the maximum density observed, the mean of the monthly max- 

 ima, the mean -of the monthly minima, and minimum observed. 



Following the table of densities are graphs of monthly mean salin- 

 ities showing the seasonal variations for many places listed in Table 1. 



The observations are made by drawing a sample of water from near 

 the surface and observing its density by means of a hydrometer. They 

 are usually made once each weekday at whatever time the observer at- 

 tends the tide gage. It may be assumed that in the course of a month 

 or a year the distribution of observations is fairly uniform over all 

 phases of the tide. At some stations situated within or near the en- 

 trance of an estuary, the density varies with the stage of the tide or 

 with the direction of the tidal current. 



The densities in Table 1 are given with respect to the density of 

 pure water at a temperature of 4°C (39.2°F) as unity. The actual den- 

 sity of the water may vary from a little less than unity for fresh wa- 

 ter at a temperature other than 4°C to approximately 1.0310 for the 

 heaviest sea water. Since the density of sea water, as observed, de- 

 pends not only upon the amount of soluble matter contained in a unit 

 volume but also upon the temperature of the water at the time the read- 

 ing was made, it is necessary to reduce the observed densities to some 

 standard temperature in order that they may be comparable. In this 

 publication the observed densities have been reduced to a standard tem- 

 perature of 15°C (59°F). The density of pure water free from air at 

 a temperature of 15°C is 0.9991. 



The salinity of sea water, denoted by the symbol o/oo, is defined 

 as the number of grams of salts contained in 1000 grams of sea water. 

 Salinity can be determined by several different methods, one of the 

 simplest being based upon the density of the water as obtained from 

 the use of the hydrometer. Table 2 gives the salinity corresponding 

 to different values of density at the standard temperature of 59*'F. 

 (15°C.) to which all densities in this publication are referred. 



For some practical uses of density data, it is more important to 

 know the density at the temperature apt to be encountered than at the 

 standard temperature. The graph. Sea Water Density at Various Temper- 

 atures, provides for converting density at 59°F (15°C) to density at 

 other temperatures. 1 



