PARTICULATE AND DISSOLVED ORGANIC CARBON IN OCEANS 209 



TABLE 1 



MEAN PERCENTAGE OF TOTAL ORGANIC 

 CARBON IN SEAWATER SAMPLES 



Mean % total organic carbon 



Particle-size 

 range, m 



>0.8 



0.025 to 0.8 

 0.003 to 0.025 

 <0.003 



and it includes amino acids, carbohydrates, lipids, organic acids, and vitamins, 

 but these are present only in trace amounts. There is a much larger pool of 

 materials that presumably are end products of metabolism and are virtually inert 

 biologically, and the composition of this fraction remains essentially unknown. 



DYNAMICS OF PRODUCTION AND CONSUMPTION 

 OF ORGANIC MATTER 



Primary Sources 



The basic source of organic matter in the sea is, of course, photosynthetic 

 fixation of carbon in the surface layer, with some slight additions from the land. 

 This organic matter then passes through a herbivore— carnivore food web, which, 

 in the open ocean consumes most of it, and most of the consumption is within 

 the upper few hundred meters. Excretory products and organisms that die a 

 natural death pass into a parallel system of scavengers consisting mainly of 

 bacteria, which gradually, in the water column or on the bottom, decompose the 

 organic material and return the mineral elements for recycling through the 

 system. 



The preceding paragraph states the traditional view of the matter, and in 

 broad outlines that view is correct for the open ocean, although recent work has 

 introduced qualifications. Moreover, it is apparent that in some shallow estuarine 

 waters the scavenger food chain is dominant, and the fauna gets its primary 

 sustenance from decomposers working on marsh grass and other terrigenous or 

 semiterrigenous sources rather than phytoplankton. There is a whole series of 

 intergradations between these and open-sea conditions. 



The Role of Nonliving Organic Matter in the Food Web 



Early considerations of the dynamics of the food web were almost solely 

 concerned with the interrelations of major groups of organisms: phytoplankton, 



