PARTICULATE AND DISSOLVED ORGANIC CARBON IN OCEANS 205 



complex and too low in concentration, compared with the great mass of 

 associated sea salts, for easy analysis. Only in the last few years have analytical 

 techniques become sufficiently sophisticated and sensitive to deal effectively 

 with this kind of problem, and the available information is still fragmentary. 



Although the concentration of nonliving organic matter is small, the total 

 amount in the world's oceans is large. A water column 1 m square extending 

 from the sea surface to a deep ocean bottom of average depth, i.e., about 

 4000 m, would contain about 4 kg C/m 2 , and the amount in all the world 

 oceans would be 10 1 2 metric tons or more. This is far in excess of the quantity 

 of living organisms in the ocean, the ratio probably being of the order of 100 : 1. 



The nonliving organic matter is derived from living organisms in the sea 

 except for a small and probably insignificant amount from terrestrial sources, 

 and the ultimate source is, of course, photosynthetic fixation of carbon in the 

 surface layer. Opinions differ as to what might be a reasonable estimate of 

 average oceanic productivity, but it almost certainly falls somewhere within the 

 general range of 50 to 200 g C m 2 year" 1 . Most of this production is 

 metabolized within the food chain. Thus the large pool of nonliving matter must 

 be the result of a slow rate of addition over a period of many years, and it 

 follows logically that most of this material must be relatively inert biologically. 

 However, a small fraction of the dissolved matter consists of amino acids and 

 other simple organic compounds. Such substances are known to be excreted by 

 animals and released as extracellular metabolites by algae, and in turn they are 

 readily utilized by bacteria. This suggests that a small percentage of the dissolved 

 matter may have a much more rapid turnover time than the general average. In 

 this respect, and in other ways that will be discussed later, the interrelations 

 between the living organisms of the sea and the nonliving matter are more 

 complicated than was realized until recently. 



DISTRIBUTION AND CHARACTER OF PARTICULATE 

 ORGANIC MATTER 



As indicated in the preceding paragraphs, there is a more or less continuous 

 spectrum of sizes of organic matter. The particulate matter is operationally 

 defined as the particles retained by a relatively fine filter, and this is a minor 

 fraction of the total organic content. The method of collection obviously does 

 not discriminate between living and nonliving matter, although subsidiary 

 analyses of chlorophyll, ATP (adenosine triphosphate), or other components of 

 living cells have sometimes been used for approximate estimates of living matter. 

 The fraction of living matter in the surface layer is variable and sometimes large 

 during periods of pronounced plankton growth. In the ocean depths it declines 

 to 1 to 10% of the total. 



Most of the available information on particulate organic matter is in terms of 

 organic carbon. Scattered data can also be found on total dry weight, particle 



