Domain of the Marine Microbiologist 9 



organisms. It sei-ves as a source of energy and building material 

 for heterotrophs. Certain organic fractions stimulate growth or 

 provide essential growtli factors (1, 44, 51). Other organic 

 fractions in sea water have inhibitoiy or antibiotic x^roperties ( 32, 

 49, 56). A fourth possible role of organic matter is to influence 

 the availabiHty of trace metals by chelation, the effect of which 

 may be beneficial or detrimental, depending upon the circum- 

 stances (47). 



TEMPERATURE AND PRESSURE 



Whereas pure water has its maximum density at 4 C and 

 freezes at C, sea water is most dense at its freezing point. The 

 freezing point of sea water is a function of its sahnity, being 

 about - 1.86 C at salinity 35%c. As sea water nears its freez- 

 ing point in polar regions and becomes more dense, it sinks and 

 fills ocean basins with cold water. This unique property of sea 

 water has far-reaching effects on the movement, oxygenation, 

 temperature distribution, and biology of water masses. At the 

 ocean surface the temperature of water ranges from its freezing 

 point to about 28 C in the tropics. Higher temperatures occur in 

 shallow water in certain localized areas. Average surface ocean 

 temperatures at different latitudes are shown in Table 3. 



TABLE 3 



Average Surface Temperature of Oceans From Equator South to Polar 

 Ice Fringe: Adapted From Sverdrup, Johnson, and Fleming, (54) 



