Settling analysis of fine sediment in salt water at concentrations low enough to preclude flocculation

Ozturgut, E.; Lavelle, J. W.

doi:10.1016/0025-3227(86)90047-2

Cited by 7 publications

(4 citation statements)

References 8 publications

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“…Several floes contain low to moderate amounts of smectite [ Nürnberg et al , 1994; Cooper et al , 1998]. Most of the <2 μm clay fraction would settle‐out if transported in suspension over distances of a few hundred kilometers, especially in the flocculated state typical of marine clays, even at low concentrations [ Ozturgut and Lavelle , 1986]. Resuspension and transport by bottom currents is unlikely because of the intervening Mendeleev Ridge and the low content of smectite in bottom sediments on the East Siberian Shelf [ Viscosi‐Shirley et al , 2003a, 2003b].…”

Section: Results: Fe Oxide Mineral Abundances and Sourcesmentioning

confidence: 99%

A Holocene record of changing Arctic Ocean ice drift analogous to the effects of the Arctic Oscillation

Darby

Bischof

2004

Paleoceanography

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[1] The Arctic Oscillation (AO) controls the configuration of the Transpolar Drift (TPD). If thicker ice from the Beaufort Gyre were exported, the volume of fresh water/sea ice in the Nordic seas would significantly increase, decreasing the formation of North Atlantic deep water. This would cool large parts of the Northern Hemisphere and affect global climate. Therefore, in order to understand how the global climate system functions, it is imperative to know how the TPD changed over the last millennium or more. The provenance of grains in a sediment core located near the confluence of the TPD and the Beaufort Gyre provides a direct proxy for changes in seaice drift owing to these circulation systems. The core has more than 200 cm of Holocene sediment, with intervals dominated by grains from the Russian shelves alternating with intervals of abundant grains from North American sources. Grains matched to Russian shelves indicate that the TPD was shifted toward North America, similar to what occurs during a more positive phase of the AO. This condition alternated with intervals where few grains matched to Russian sources, presumably because the TPD was restricted to the Russian half of the Arctic, far from the core site. During the last 1300 years, increased influx of Russian grains occurred approximately every 50-150 years. This fluctuation might represent the long-term oscillation of the AO, which modulates the same TPD shift today.

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Section: Results: Fe Oxide Mineral Abundances and Sourcesmentioning

confidence: 99%

A Holocene record of changing Arctic Ocean ice drift analogous to the effects of the Arctic Oscillation

Darby

Bischof

2004

Paleoceanography

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“…Settling analyses on the coarse (>63 µ ) fraction of particulates were performed in freshwater using a 1-L glass cylinder with a diameter of 6 cm and with large-orifice (2-mm) pipets. The use of freshwater stems from the following considerations: (1) the fibrous content of the coarse fraction dictated gravimetric rather than Coulter Counter volumetric analysis; (2) gravimetric analysis required mass concentrations on the order of 100-200 mg/L in order to get reliable weight estimates from settling experiment subsamples having small volume;…”

Section: Methodsmentioning

confidence: 99%

“…The resulting aliquots had a volume of 25 mL and a concentration of 1-10 mg/L. This small volume and low concentration dictated that the particle content be measured by electronic particle counter rather than by gravimetry (1,14), though optical measurements might also have been used for this purpose (7,15). Aliquots were measured by Coulter Counter with 70-and 200-^m-aperture tubes.…”

Section: Methodsmentioning

confidence: 99%

“…The key to preventing flocculation during settling is to restrict the settling stage to low particulate concentration for which the frequency of particle-to-particle contact is low. Ozturgut and Lavelle (1) found that the settling of clays in seawater was not affected by flocculation when concentrations were 7 ppm or less. On the basis of that result, particulate concentrations near 10 mg/L (~5-10 ppm) were deemed suitable for conducting these measurements.…”

Section: Introductionmentioning

confidence: 99%

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Settling speeds of sewage sludge in seawater

Lavelle¹,

Ozturgut²,

Baker³

et al. 1988

Environ. Sci. Technol.

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w Laboratory analyses of sludges from four treatment plants were performed to determine solid content, size distributions, and settling spectra of sludge particulates in seawater, The settling experiments were conducted after partitioning samples by sieving into coarse and fine particulate fractions. For the fine fraction, experiments proceeded after controlled mixing of samples with filtered seawater to particulate concentrations low enough ( N 10 mg/L) that flocculation was limited during subsequent measurement periods. Results show that 14.6-47.3% of the sludge particulates by weight had diameters greater than 63 pm, with at least 5% exceeding 250 pm. Median settling velocities of this fraction ranged from 6 X to 3 X 10-1 cm/s. The bulk of the particulates were smaller in diameter, and these flocculated in seawater. Resulting aggregates had median settling velocities by volume ranging from 7 X lo4 to 3 X cm/s, with less than 10% of the particles settling more slowly than 10" cm/s. IntroductionThe ability to predict the fate of sewage sludge after ocean discharge requires knowledge of its physical properties, particularly the settling speeds of its constituent particles. Yet this measurement has not been satisfactorily made because of the difficulties of settling measurements in situ and because laboratory studies are beset with their own special set of problems. Specifically, adequate laboratory settling velocity measurements bearing on the fate of ocean discharges of sludge depend on (1) the creation of flocculated particles resembling those found in the ocean, a creation process that is dependent on poorly known ocean mixing conditions, and on (2) being able to prevent the change in the physical properties of the particles after the formation process and during the settling measurements. Few results of settling experiments for sludge particulates are not confounded by continued flocculation during the measurement period. The laboratory work described here primarily addresses the second aspect of this problem, though an attempt was made to create flocculated particles under low shear and during increasing dilution, conditions qualitatively resembling those found in the ocean during the floc formation period.The key to preventing flocculation during settling is to restrict the settling stage to low particulate concentration for which the frequency of particle-to-particle contact is low. Ozturgut and Lavelle (I) found that the settling of clays in seawater was not affected by flocculation when concentrations were 7 ppm or less. On the basis of that result, particulate concentrations near 10 mg/L (-5-10 ppm) were deemed suitable for conducting these measurements. This is also a desirable choice of concentrations because such concentration levels are near those expected in the ocean tens of minutes past the time of discharge. For example, concentrations of 10-40 mg/L were measured

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Suspended sediment transport across a tidal flat

Pejrup¹

1988

Marine Geology

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Settling analysis of fine sediment in salt water at concentrations low enough to preclude flocculation

Cited by 7 publications

References 8 publications

A Holocene record of changing Arctic Ocean ice drift analogous to the effects of the Arctic Oscillation

A Holocene record of changing Arctic Ocean ice drift analogous to the effects of the Arctic Oscillation

Settling speeds of sewage sludge in seawater

Suspended sediment transport across a tidal flat

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