PARTICULATE AND DISSOLVED ORGANIC CARBON IN OCEANS 213 



large aggregates have a sinking rate of the order of 1 to 2 m/day and would 

 require some years to reach bottom if they maintained their integrity 

 throughout the descent. 1 Smaller particles would, of course, require longer. Of 

 some significance in this respect is the report of McGill 30 that total organic 

 phosphate varies regionally in relation to geographical variations in productivity. 

 Most of this organic phosphate can be assigned to the filter-passing fraction 

 rather than particulates, so that sinking is not directly implicated. However, the 

 so-called dissolved organic carbon is more nearly uniform regionally and 

 presumably represents an older fraction that has had more time to get uniformly 

 dispersed. 



An abundant literature could be cited in support of the conclusion that the 

 whole biological system, surface to bottom, varies regionally more or less in 

 accord with levels of surface productivity. Riley 31 reviewed some of this 

 literature, chosen from a few selected areas. It was apparent there that the 

 character of the food web can vary considerably from one area to another, with 

 major emphasis on predators in some areas and on decomposers in others. 

 Nevertheless, the generality holds and is that the surface production is in one 

 way or another transported from surface to bottom, affecting the production of 

 zooplankton, neckton and benthos, the quantity of small heterotrophic algae, 

 nonliving particulate matter, and probably, to a limited degree, some of the 

 filter-passing organic components. The reasons for this are not clearly under- 

 stood, and explanations that can be presented are largely hypothetical. 



The most important mechanism for vertical transfer is probably the so-called 

 "ladder of life." 22 ' 23 The nonliving organic matter and associated ultraplankton 

 are eaten to some extent by bathypelagic copepods, although, for the 

 above-mentioned reasons, there is some question as to whether they are a major 

 food item. Nor is there any solid information as to the degree of significance of 

 animal excretion in promoting in situ formation of aggregates and the growth of 

 small heterotrophs. The correlation between the size of the animal population 

 and the amount of small particulate matter suggests this kind of reciprocal 

 relation. Experimental information tends to support two postulates: (a) 

 excretion of soluble substances could promote both the growth of heterotrophs 

 and the accretion of nonliving aggregates, and (b) accompanying consumption of 

 aggregates by the animal population would tend to stimulate further production 

 of particulate matter. The latter might be enhanced by excretion of unconsoli- 

 dated fecal material and of bacteria that are in a more active state of growth 

 than those in the water column. 



This general line of reasoning is supported by the observed fact that the 

 amount of particulate organic matter does not decrease systematically with 

 depth, which it might be expected to do if a significant amount were eaten or 

 decomposed as it sinks through the water column. On the basis of this 

 observation, it has been postulated 32 that a dynamic balance exists between 

 consumption and accretion of particulate matter in the bathypelagic zone, 

 although little was known then of the processes involved. Knowledge is still very 



