Chapter II — 15 — The Marine Envirooment 



either directly or indirectly. In the latter category may be mentioned the 

 effect of water movements upon the temperature of the marine environ- 

 ment in various regions and upon the chemical composition of sea water. 

 Vertical mixing or upwelling tends to bring nutrients to the euphotic zone. 

 The greater abundance of microorganisms found in regions where warm 

 and cold water meet or in regions of upwelling has already been mentioned. 



Salinity, chlorinity, and density: — The concentration of total solids 

 dissolved in sea water is usually expressed as salinity in terms of parts per 

 thousand, per mille, or grams of solids per kilogram of sea water, for which 

 the symbol °/oo is used. For biological purposes it usually suffices to state 

 the salinity as the nearest whole number or to the first decimal place, but 

 because minute differences in salinity materially influence the dynamic 

 stability of water masses, oceanographers give the sahnity to the second 

 decimal place. 



Unless diluted by heavy rainfall, melting ice, or rivers, the salinity of 

 surface sea water generally ranges from $$ to 37°/oo. However, in regions 

 of considerable fresh-water dilution, as in the Gulf of Bothnia, for exam- 

 ple, the salinity may approach zero. In isolated regions where surface 

 water evaporates rapidly, as in the Red Sea or in tide pools, the salinity 

 may exceed 40^/00 for short periods of time. The salinity of the Dead Sea, 

 like that of Great Salt Lake, sometimes reaches 320V00 while that in the 

 Black Sea is only 16 to 23^/00, but these inland bodies of water are far re- 

 moved from the great oceans of the world. The salinity of deep or bottom 

 water of the oceans varies within narrow limits, approximately 34-6 to 

 35V00 (SvERDRUP et al., 1942). 



The chlorinity is the number of grams of halogens, calculated as chlo- 

 rine, precipitable by silver nitrate, contained in a kilogram of sea water. 

 Since analytical procedures for determining the chlorinity of sea water are 

 simpler and more precise than those for determining salinity directly, and 

 since there is a constant relationship between salinity and chlorinity, the 

 salinity of sea water is generally calculated from its chlorinity: Salinity = 

 0.03 + 1.805 ^ chlorinity. 



The density or specific gravity of sea water can be calculated from the 

 chlorinity if the temperature is known. At 0° C. the density equals 

 0.999,931 + o.ooi,47o,8Cl — 0.000,00 1, 5 7 CP + o.ooo,ooo,o39,8Cl^. The 

 density may also be obtained by reference to Knudsen's (1901) Hydro- 

 graphical Tables. Roughly the density of sea water ranges from 1.024 to 

 1.030. 



For hydrographical purposes the density of sea water may be deter- 

 mined accurately to the fifth place. Since the first two figures are always 

 the same, it is practical to express the density by omitting the first two 

 figures and shifting the decimal point three places to the right so that a 

 density of i. 02814, for example, is expressed simply as 28.14. 



Osmotic and hydrostatic pressure: — The osmotic pressure of sea 

 water at any given temperature may be calculated from its salinity or 

 chlorinity. According to Thompson (1932), the freezing point of sea 

 water. A, equals — 0.0966CI — 0.0000052CP. From the colligative 

 properties of dilute solutions it is known that when A is — 1.86° C, the 

 osmotic pressure is 22.4 atmospheres. Thus the osmotic pressure of sea 



water at 0° C. approximates—^ X A or 12.04 X A. Thompson (1932) 



