206 RILEY 



counts, a few other elements besides carbon, and some of the biochemical 

 constituents. However, the preponderance of information on organic carbon 

 makes it the most suitable analysis for discussion of regional and depth 

 distribution. 



Riley 1 in 1970 summarized the then-available data on the distribution of 

 particulate organic carbon. Most of the values in the surface layer were in the 

 range of 25 to 300 /ig C/liter except in a thin surface stratum where the 

 quantities were considerably larger. Below the surface layer there was a 

 transition zone of decreasing concentration to a depth varying in different areas 

 from 200 to 800 m, and below that there was no systematic decrease with 

 depth. The mean concentration in deep water varied in different parts of the 

 North Atlantic Ocean from 12 to 50 /ig C/liter. 



In this early work the water column was not sampled at closely spaced depth 

 intervals. Later and more detailed work 2,3 has demonstrated significant 

 variations in individual samples, even at closely spaced depth intervals. Thus 

 there is considerable evidence of layering and microstructure, although the scale 

 of these variations has not yet been determined accurately. 



Similar layering in the Pacific Ocean has been described. 4 ' 5 Nakajima 5 had an 

 extensive series of stations in the North Pacific, most of which showed a 

 decrease from the surface to a minimum at the bottom of the mixed layer and a 

 secondary maximum at mid-depths. In deep water there was no systematic 

 decrease, as in the North Atlantic. However, there may be exceptions to this in 

 areas where there is layering of major water masses. There are mid-depth and 

 deep-water maxima in the South Pacific associated with intrusions of Antarctic 

 Intermediate Water and Circumpolar Water. 6 



Compilation of data on regional distribution in the Atlantic Ocean 1 showed 

 high values in rich upwelling areas off the west coast of Africa and moderately 

 high ones in temperate and boreal waters. Minimal values were obtained in 

 poorer areas of the subtropics and tropics. Thus there appeared to be a 

 correlation between surface productivity and total particulate organic matter, 

 and this was true of deep water as well as the surface layer. 



This picture of geographical distribution was compiled from the results of 

 various investigators, who used slightly different methods, so that one might 

 question whether or not the data were sufficiently comparable to warrant 

 quantitative regional comparison. However, more recently Nakajima 5 has 

 obtained similar results in a broad regional survey of the North Pacific Ocean 

 using methods that were comparable throughout. The fact that deep water as 

 well as surface particulate matter is correlated with surface productivity is not 

 fully understood, although several possible reasons can be given. Discussion of 

 this problem is relegated to a later section. 



Visually, the most obvious components of the nonliving particulate fraction 

 are fluffy amorphous masses of brownish material. Seen in the free floating 

 state, they are more or less spherical, with numerous internal spaces that harbor 

 bacteria, small algae, and protozoa. 7 Histochemical staining shows that they are 



