EXPERIMENTAL TESTS FOR PARTICLE SIZE-DEPENDENT BIOTURBATION IN THE DEEP OCEAN

The potential for particle size-dependent bioturbation rates was experimentally tested at 1,240 m in the Santa Catalina Basin (eastern Pacific). Spherical glass bead tracers in five size classes (8-16, 17-31, 32-62, 63-125, and 126-420-mu-m) were spread over the sediment surface and tube cored 997 d later. Downcore concentrations of glass beads were enumerated in each of thc five size categories and Page's L-test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer. In all cores the null hypothesis was rejected; finer tracers penetrated deeper into the sediment. In two of the three cores, vertical biodiffusivities were computed from concentration profiles of downcore tracers. These also showed size dependence, with biodiffusivities ranging from 1 cm2 yr-1 for the 8-16-mu-m fraction to 0.1 cm2 yr-1 for the 125-420-mu-m size class. These data demonstrate that vertical bioturbation rates are particle size-dependent in Santa Catalina Basin. The likely cause is preferential ingestion and downward transport of fine particles by deposit feeders.