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15 - The Floe Camera Assembly
- Edited by James P. M. Syvitski
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- Book:
- Principles, Methods and Application of Particle Size Analysis
- Published online:
- 28 January 2010
- Print publication:
- 26 July 1991, pp 209-222
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Summary
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).
13 - Interlaboratory, interinstrument calibration experiment
- Edited by James P. M. Syvitski
-
- Book:
- Principles, Methods and Application of Particle Size Analysis
- Published online:
- 28 January 2010
- Print publication:
- 26 July 1991, pp 174-194
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Summary
Introduction
There has been a historical need for sedimentologists to refine the characterization of both particle size and shape. Automated sizecharacterization instruments have improved on “classical” techniques, such as the sieve and pipette method, in terms of speed and precision. However, many of these instruments provide a size frequency distribution of particle diameters from a population of sediment grains by proxy (i.e., by converting a particle's cross-sectional area, surface area, volume, settling velocity, or some other form of particle behaviour, to particle diameter). Some techniques, such as the settling tube, may involve user-built instruments not yet calibrated in the traditional analytical sense. To this end, the International Union of Geological Sciences – Committee on Sedimentology (IUGS–COS) sponsored this study to compare the results from automated instruments that measure the frequency distribution of grain diameters in geological samples. This chapter reviews some of the previous attempts at interlaboratory or interinstrument calibration, discusses the philosophy and preparation of geological standards (silts and sands), and presents new results with recommendations for future experiments.
Grain size and calibration standards
The size of a particle is not uniquely defined, except for the most simple of geometric objects – the sphere. For natural and irregularly shaped particles, size depends on the method of measurement. Allen (1968) provides a number of differing definitions of particle size, including surface diameter, volume diameter, drag diameter, projected area diameter, free-falling diameter, Stokes's diameter, sieve diameter, and specific surface diameter.
4 - Principles, design, and calibration of settling tubes
- Edited by James P. M. Syvitski
-
- Book:
- Principles, Methods and Application of Particle Size Analysis
- Published online:
- 28 January 2010
- Print publication:
- 26 July 1991, pp 45-63
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Summary
Introduction
Over the past fifty years, the textural characterization of an unlithified sample of sandy sediment has been accomplished mainly by sieving and settling tube analysis. Both methods provide a mass frequency distribution of particle size, with the effects of particle shape and size combined. Settling tube analysis is additionally affected by particle density. Sieving became the early standard technique, accepted by both civil engineers and sedimentologists. Standard sieves were mass produced at a variety of mesh sizes, and once sieving time and tapping frequency were agreed upon, interlab precision was acceptable (<±0.25ø, where ø = −log2d and d is particle diameter in mm). Sedimentary petrologists, in their study of lithified sedimentary deposits, sized and identified sedimentary particles under a microscope using thin sections from rocks. Sieving and thin-section methods dominated sediment laboratories until the mid-1970s. With the proliferation of microcomputers in the 1980s, sieving has given way to settling tube analysis, and manual thin-section analysis has given way to image analysis.
The basic justification for settling tube analysis is that the settling velocity of a particle is a more fundamental dynamic property than any geometrically defined measure of size (i.e., sieving, thin sections, image analysis) with reference to its behaviour in a hydrodynamic environment (Gillespie & Rendell, 1985). Because particle mobility in liquids (air, water) is dependent on the ratio between shear velocity and settling velocity (Francis, 1973), the settling velocity distribution and therefore the “sedimentation diameter” distribution is argued to be more valid for the characterization of sand texture than sieve-determined size distributions (Middleton, 1976; Bridge, 1981).