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Measurements of settling particle flux not only clarify a variety of oceanic biogeochemical processes but also aid the interpretation of the sedimentary record. Particle settling is the primary mechanism for transferring dissolved and suspended materials from the water column to the sediments; however, scavenging and recycling alters the flux and composition of raining particles. Consequently, the burial rates of elements and compounds generally do not equal the particulate rain rate.
A major focus of this paper will be the comparison between the burial rate of materials that form the sediment record and the rain rate of particles that settle through the water column. From this comparison we can determine the rate of recycling or benthic flux of materials that settle to the seafloor. In effect, the benthic flux is the exchange rate of solutes between the sediment and the overlying water column. This exchange transforms raining particulate material into the sedimentary record. In its simplest form the benthic equation is:
Rain rate of any particulate component = Burial rate of that component + Benthic flux
The rain rate is the particulate flux that reaches the bottom for any component, and the burial rate is the preservation rate of that component in the sediment.
The direct measurement of particle flux has followed important developments in marine technology. Deployment and recovery of deep ocean moorings, which position particle collectors throughout the water column, are now routine. A variety of these particle collectors (commonly called sediment traps) are in current use (Soutar et al., 1977; Blomqvist and Hakanson, 1981; Dymond et al., 1981; Gardner, 1980; Honjo and Doherty, 1988). Most are cylinders or funnels in which particles enter through a baffle at the top and settle into a sample cup where a bactericide is maintained at a concentration capable of inhibiting decomposition of the sample. Many designs have timer-controlled sample changers that can collect a time series of settling particles over preset intervals.
Sediment traps work as collectors of settling particles because large, rapidly settling forms dominate the particle flux in the oceans (McCave, 1975). A number of recent studies have shown that these large particles are either amorphous aggregates of smaller particles commonly called marine snow (Alldredge and Silver, 1988) or zooplankton fecal pellets ((Urrere and Knauer, 1981; Pilskaln and Honjo, 1987). As a result of the rapid settling, a variety of sediment trap designs have similar efficiencies for collecting settling particles in the low current regime of the open ocean. These large particles settle through the entire water column of typical ocean depths (5000 m) in one to two months.
In this study we will summarize and evaluate the particle flux measurements made with sediment traps developed at Oregon State University between 1980 and 1988 (Table 9.1). The OSU trap is a single-cone modification of a design originally developed by Andrew Soutar (Soutar et al., 1977). It features all plastic or fiberglass construction, a two-to-one height to diameter cone, a one cm by five cm baffle at the top of the cone, and a 10 cm wide lip at the top of the cone that limits turbulence at the mouth of the cone. The trap has evolved from a five-cup, sequential collector to the current model that has a 15-cup collector for enhanced temporal resolution of the particle flux. In
TABLE 9.1 Location and Date of Sediment Trap Experiments