Introduction

Visual observations of suspended sediment in coastal marine waters and in the deep ocean have confirmed that the formation of flocculated or agglomerated sediment, commonly identified as marine snow (Suzuki & Kato, 1953), is an important mechanism in the transport of sediment to the seafloor (Nishizawa et al., 1954; Shanks & Trent, 1980; Farrow et al., 1983). This is particularly true for fjords (Syvitski et al., 1985) and deep estuaries (Eisma et al., 1978), but is common to all marine environments (Kranck, 1984). Primary sediment particles in the ocean are too small to be seen with the unaided eye. The particles observed visually from submersibles are therefore in the form of floccules. The most important effect of flocculation and related processes is in controlling the net vertical flux of particles through the water column. This in turn has important implications to the fill of sedimentary basins (Syvitski et al., 1988), and in controlling the fate of pollutants (Eisma, 1981). Sampling individual floes, or obtaining measurements on the settling rate of individual particles, however, has proved very difficult (Gibbs, 1982; Kranck, 1984).

All water sampling techniques break up the in situ structure of floes, leading to gross errors in estimating the flux of sediment to the ocean floor (McCave, 1975). For instance, water samplers and submerged pumps can alter the characteristics of flocculated particles through mechanical interference (Gibbs, 1981).