The oceanic microcosm of particles.

Analyses of suspended particulate matter larger than 1 micrometer, filtered from thousands of liters of surface and deep waters during GEOSECS expeditions to the Atlantic and Pacific oceans, have provided new information on the nature and time scales of chemical processes associated with the particles. Trace element and radionuclide data show that particles scavenge trace elements such as Th, Pu, Fe, Pb, and Cu from the ocean column, thereby controlling their concentrations. For other elements, however, particles are a source: carbon and silicon, for example, are introduced at depths as sinking particles dissolve. Studies of both particulate concentrations by filtration of seawater and particulate fluxes by using sediment traps seem necessary to delineate the intricate nature of chemical processes in the oceans.