Wakeham and Lee (1993; Fig. 13.27) assembled the scattered data from trapping
studies in oligotrophic areas, comparing at progressively greater depths the downward
flux rates of specific components of the organic matter. Much of the consumption and
metabolic remineralization of sinking organic matter occurs in the upper 500 m.
Below that depth the continued decrease is roughly exponential (somewhat like the
Martin curve), which Wakeham and Lee represented by estimating “half-depths”, the
distances required to reduce the flux by half. Amino acids (protein particles) are
removed faster (shorter half depth) than fatty acids, and those are removed faster than
the total of all organics. Thus, food quality of sinking organic matter changes
downward. That is demonstrated by the substantial shifts in amino-acid composition.
Amino acids in sediments (residual after much more metabolic processing) are altered
even more. Only moderately refractive organic matter reaches the seafloor to serve as
the diet on which an elaborate diversity of bacterial, protist, and metazoan life
subsists.
Fig. 13.27 Vertical profiles of (a) flux of particulate organic carbon (POC), (b) fatty
acids, and (c) amino acids measured by several trap studies in oligotrophic, oceanic
areas. Rates of downward decrease in flux are indicated by depth changes required to
reduce flux by half (Z1/2).
(^) (After Wakeham & Lee 1993.)