INTRODUCTION 
The summaries of sea water densities presented in this publication are based on 
observations made in Atlantic harbor and coastal waters through the year 1952. 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 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 observations 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 ob- 
servations. Maximum and minimum densities are shown for each year inwhich observations 
were made, whether or not the observations covered the whole year. In all cases the 
yearly extremes are from the months of the year forwhich 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 their corresponding salinities, the maximum density observed, the 
mean of the monthly maxima, the mean of the monthly minima, and minimum observed. 
Following the table of densities are graphs showing the seasonal variation in 
salinity at stations for which the observations covered five years or more. 
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 week- 
day at whatever time the observer attends 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 entrance of an 
estuary, the density varies with the stage of the tide or with the direction of the 
tidal current. 
The densities in Table ] are given with respect to the density of pure water at 
a temperature of 4°C (39.2°F) as unity. The actual density of the water may vary from 
a little less than unity for fresh water at a temperature other than 4°C to approximately 
1.0310 for the heaviest sea water. Since the density of sea water, as observed, depends 
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 reading was made, it 1s necessary to re- 
duce 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 stand- 
ard temperature of 15°C (59°F). The density of pure water free from air at a temper- 
ature of 15°C is 0.9991. 
The salinity of sea water 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 den- 
sity at the standard temperature of 59°F. (15°C.) to which all densities in this pub- 
lication 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 Temperatures, provides for converting density at 59°F (15°C) 
to density at other temperatures. 
The following publications complete this series: 
Special Pub. 278. Surface Water Temperatures, Atlantic Coast, North and South 
America. 
Special Pub. 280. Surface Water Temperatures, Pacific Coast, North and South 
America and Pacific Ocean Islands. 
Special Pub. 281. Density of Sea Water, Pacific Ocean. 
