surface waters. As this debris sinks under the influence of gravity 
toward the sea floor, oxidation and solution gradually return the 
constituent elements to their dissolved form. This downward particu- 
late transport process works against the homogenizing influence of 
physical mixing and tends to enrich the deep sea in many chemical spe- 
cies. Thus, in order to understand the dispersion of a given element 
through the world ocean, we must comprehend both physical mixing and 
particulate transport phenomena. Organic productivity studies tell us 
something of the generation of particles; and sediment studies, some- 
thing of the fraction surviving destruction. Still, the details of 
the intermediate steps are essentially unknown. A large fraction of 
the phosphate, nitrate and other essential nutrients is redissolved 
and brought back to the surface by advection and diffusion, we recog- 
nize --- and it is this action that is so important in determining 
organic productivity in different regions of the sea. 
How fast is the material returned to the surface? How 
do the particulate fluxes of the different trace elements, nutrients 
and isotopes vary in different parts of the ocean? How much of these 
constituents is oxidized at different depths and how much settles to 
the bottom? These questions, almost unanswerable today, can be settled 
by studies of the vertical and horizontal distribution of radioisotopes 
and trace elements. Since the radioactive isotopes themselves partici- 
pate in the particulate and biological cycles, we must investigate the 
distribution of “coupled" radioactive and stable isotopes in order to 
separate the effects of fluid mixing and particulate flux. Thus, the 
