774 



TABLE 889.— PERCENTAGE AREA OF DEPTH ZONES IN THE OCEANS* 



For reference, see footnote 302, p. 773. 



TABLE 890.— PHYSICAL PROPERTIES OF SEA WATER (Fig. 34) 



Temperatures in the sea range from — 2° to 30°C. The lower limit is set by the for- 

 mation of ice and the higher limit by the balance between incoming radiation, back radia- 

 tion, and evaporation. 



Pressures in the sea vary from zero at the sea surface to about 1,000 atm in the greatest 

 depths (10,000 m). Standard unit is the bar = 10 8 dynes/cm 2 . Approximately 10 m of 

 sea water = 1 atm. 



Concentration of the dissolved constituents varies from nearly zero in river mouths to 

 40°/o O (parts per thousand) in isolated seas in arid regions. In most ocean waters the 

 total solids are between 33 and 37°/ 00 . In addition, sea water contains dissolved gases, 

 dissolved organic matter, and variable amounts of particulate material of biological or 

 terrigenous origin. 



Salinity is defined as the total amount of solid material in grams in one kg of sea 

 water when all carbonates are converted to oxides, the bromine and iodine replaced by 

 chlorine, and all organic matter completely oxidized. 



Chlorinity, determined by titration with AgNC>3, is essentially equal to the amount of 

 chlorine in grams in one kg of sea water when all the bromine and iodine have been 

 replaced by chlorine. 



Salinity — 0.03 + 1.805 X Chlorinity (°/oo) 



Distribution of temperature and salinity is most variable in the surface layers. 

 Low temperatures occur in high latitudes with relatively low salinities. In the Tropics 

 surface temperatures and salinities are high. The great ocean basins are filled with high- 

 density water produced in high latitudes during the winter when ice forms or when water 

 of high salinity is cooled. Deep temperatures are therefore generally between 0° and 2°C. 

 Convection and wind mixing produce a surface layer in which uniform conditions prevail. 

 This may be as thick as several hundred meters. Immediately beneath this there is a 

 rapid change in temperature called the thermoclinc. Diurnal variations of temperature 

 at the surface rarely exceed 1°C. Annual variations of surface temperature are greatest 

 in midlatitudes (about 10° C). Annual variations diminish with depth and rarely extend 

 below 200 m. 



Density of sea water is a function of salinity as well as temperature and pressure. The 

 range in values is from 1.00 to about 1.04 g/cm 3 . Most of the other properties are functions 

 of temperature, salinity, and pressure. The difference from the values for pure water 

 depends then on the effects of the dissolved organic compounds. Light absorption and 

 color will also be primarily determined by suspended or dissolved debris. Processes of 

 heat conduction, diffusion, and transfer of momentum are dominated by turbulent water 

 movements and consequently the laboratory coefficients of conductivity, diffusion, and 

 viscosity have to be replaced by "eddy" coefficients of vastly greater magnitude. 



Absorption of light. — Water is essentially opaque to electromagnetic radiation except 

 in the visible spectrum. Below several hundred meters, even in the clearest water, all the 

 solar radiation is absorbed. (See Tabic 891 and fig. 35.) In coastal waters that contain 

 suspended debris, the radiation may be absorbed in only a few meters. The rapid absorp- 

 tion of radiation limits photosynthesis to the surface layers. 



Evaporation. — The principal source of heat is radiation from sun and sky. The chief 

 heat losses are due to long-wave radiation to space and evaporation. Evaporation is 

 greatest when the air is dry and colder than the water. Regional variations are generally 

 between 50 and 150 cm/year. 



SMITHSONIAN PHYSICAL TABLES 



