Particles play a special role in the ocean. Such materials are introduced 

 primarily by weathering processes and biological activities, but also 

 by volcanism and chemical processes in the upper layers. Once formed, 

 these materials settle, usually slowly, toward the seafloor and provide 

 a site for various reactions. The bulk composition, size distribution and 

 light-scattering properties have received considerable attention, par- 

 ticularly by Soviet investigators. However, we have only limited under- 

 standing of the changes that occur in and on particles after formation. 

 Such particles play a key role in heavy metal transport, but the relative 

 role of various particle types is not well understood, nor are we certain 

 of the importance or rates of surface reactions on the particles. 



Particles entering the sea and particles residing in the upper layers 

 may be collected into aggregates with greater settling velocity and 

 less areal exposure to seawater. Filter feeders ingest, grind, and digest 

 particles, ultimately expelling them as fecal pellets, which settle far 

 faster than the individual component particles. Moreover, the pellets 

 are largely isolated from seawater by coatings, but they are fragile, often 

 breaking soon after formation, and they may in turn be reingested, 

 digested, and reformed. Nevertheless, a vast rain of such materials 

 moves toward the seafloor. Their role in vertical transport depends on 

 transfer across their boundaries, and their ability to remain intact under 

 physical stress and bacterial attack. 



Those pellets that reach the seafloor are broken or altered, with their 

 contents subsequently being transformed by bacteria and ultimately 

 released to the water and sediment. Most settling pellets are probably 

 broken up by collection methods, and gentler collection techniques 

 and more careful studies of the amounts, settling rates, and surface 

 chemistry of such materials are needed. 



Particles of continental detritus may settle rapidly in the coastal 

 zone or slowly into the abyss. During settling these particles undergo 

 varying degrees of equihbration with dissolved species in the water, 

 exchanging ions, adsorbing, and even to some extent dissolving. Since 

 the bulk of inorganic detritus enters at the ocean surface, rapid reactions 

 will aff'ect surface water chemistry, whereas slower reactions may have 

 greater efl'ect during the long slow fall into the depths. Our understanding 

 of the rates of these reactions and their response to temperature and 

 pressure is poor. The influence of squeezing temperatures, when diff'erent 

 from the in-sitii temperature, on the apparent composition of interstitial 

 waters shows that many equilibria are markedly altered by temperature 

 changes. Such factors influence the role of particles in redistributing 

 chemicals in the sea, but we cannot assign quantitative values to this 

 role. 



The sinking of the tests of marine organisms plays a well-established 

 role in the distribution of the nutrients in the ocean. A spectrum of trace 



37 



