in the surface layer by ^14 C-uptake (data from Barber 1996, see Fig. 11.34) The effects
of equatorial upwelling provided strong gradients of production rates from the more
eutrophic equator out into oligotrophic waters at 10°N and 12°S. Flux of organic
matter was estimated from trap collections above the seafloor (Fig. 13.26b), and
reflects the same gradient. The fraction of primary production reaching the bottom
along this transect is about 0.4%, i.e. four parts per thousand remain after filtering
down through the 4500 m water column. Benthic respiration rates (see Chapter 14)
implied carbon metabolism rates of the same general magnitude (Fig. 13.26c).
Sediment traps at a depth of only 105 m produced organic mass flux rates only 3–6%
of the primary productivity (Hernes 2001). Most organic matter is consumed very
close to the depth at which it is produced by photosynthesis.
Fig. 13.26 Comparison along a trans-equatorial transect in two seasons (February–
March observations were from a period of fully developed El Niño) of (a) primary
production, (b) flux of organic carbon above the bottom, and (c) the rate of benthic
remineralization based on oxygen consumption (solid squares and open squares with
crosses were collected on different expeditions).
(After Berelson et al. 1997.)