Settling Velocity and Grain Shape of Maerl Biogenic Gravel

Joshi, Siddhi; Duffy, Garret; Brown, Colin

doi:10.2110/jsr.2014.51

Cited by 17 publications

(29 citation statements)

References 32 publications

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“…Under a negligible shear rate, aggregates that formed under low plume concentrations of 35 mg L -1 showed higher size-specific settling velocities than similar-sized particles under higher plume concentrations. The present results indicate that aggregate shape, which is often neglected in modeling equations (Joshi et al, 2014) for computational reasons, may be an important regulating factor of the size-specific settling velocity ( Figure 4A) resulting in a decrease in effective density, as discussed by Mikkelsen and Pejrup (2000). The present results revealed that size-specific settling velocities of plume aggregates >100 µm deviate from typical model-based calculations using either Stokes' or Ferguson and Church's (2004) recalculated values for w s , as shown in Figure 6.…”

Section: Settling Velocities Of Aggregated Plume Particlesmentioning

confidence: 53%

Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plumes in the Clarion Clipperton Fracture Zone (eastern-central Pacific)

Gillard¹,

Purkiani²,

Chatzievangelou³

et al. 2019

Elementa: Science of the Anthropocene

104

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The anthropogenic impact of polymetallic nodule harvesting in the Clarion-Clipperton Fracture Zone is expected to strongly affect the benthic ecosystem. To predict the long-term, industrial-scale impact of nodule mining on the deep-sea environment and to improve the reliability of the sediment plume model, information about the specific characteristics of deep-sea particles is needed. Discharge simulations of mining-related fine-grained (median diameter ≈ 20 μm) sediment plumes at concentrations of 35–500 mg L–1(dry weight) showed a propensity for rapid flocculation within 10 to 135 min, resulting in the formation of large aggregates up to 1100 μm in diameter. The results indicated that the discharge of elevated plume concentrations (500 mg L–1) under an increased shear rate (G ≥ 2.4 s–1) would result in improved efficiency of sediment flocculation. Furthermore, particle transport model results suggested that even under typical deep-sea flow conditions (G ≈ 0.1 s–1), rapid deposition of particles could be expected, which would restrict heavy sediment blanketing (several centimeters) to a smaller fall-out area near the source, unless subsequent flow events resuspended the sediments. Planning for in situ tests of these model projections is underway

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Section: Settling Velocities Of Aggregated Plume Particlesmentioning

confidence: 53%

Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plumes in the Clarion Clipperton Fracture Zone (eastern-central Pacific)

Gillard¹,

Purkiani²,

Chatzievangelou³

et al. 2019

Elementa: Science of the Anthropocene

104

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“…The prediction for calcified macroalgae (and corals) is for decreased calcification with increasing seawater CO 2 , and for decreased organic productivity with increasing CO 2 if the decreased calcification in high CO 2 limits growth [31]. However, work on shallow-water marine CO 2 seeps shows that the prediction is not always borne out [32].…”

Section: Futurementioning

confidence: 99%

Blue carbon: past, present and future, with emphasis on macroalgae

Raven

2018

Biol. Lett.

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Blue carbon did not originally include macroalgal ecosystems; however evidence is mounting that macroalgal ecosystems function in marine carbon sequestration. The great majority of present day marine macroalgal net primary productivity (NPP) involves haptophytic algae on eroding shores. For these organisms the long-term storage of particulate organic carbon involves export from the site of production of biomass that has evaded parasites and grazers, and that some of the exported biomass is sedimented and stored rather than being mineralized en route by detritivores (microbes and fauna). Export from eroding shores, and subsequent storage, of haptophytic marine macroalgal particulate organic carbon could have started by 1.6 Ga. Storage on depositing shores close to the site of NPP by rhizophytic macroalgae and then by rhizophytic coastal seagrasses, tidal marshes and mangroves began not less than 209 Ma ago. Future increases in surface ocean temperatures may bring tropical marine macroalgae to their upper temperature limit, while temperate marine macroalgae will migrate poleward, in both cases assuming that temperature increases faster than genetic adaptation to higher temperature. Increased CO 2 in the surface ocean will generally favour uncalcified over calcified marine macroalgae. This results in decreased CO 2 release from decreased calcification, as well as decreased ballasting by CaCO 3 of exported particulate organic carbon resulting in decreasing sedimentation. While much more work is needed, the available information suggests that macroalgae play a significant role in marine organic carbon storage.

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“…Cool‐water carbonates have been far less studied than their warm water counterparts (James & Clarke, ). In these environments, bioclastic sediments are mainly composed of mollusc (bivalves and gastropods) skeletal remains (Kidwell, ), or are less frequently composed of coralline algae (Joshi et al ., , ), bryozoans or crustaceans.…”

Section: Introductionmentioning

confidence: 99%

Threshold of motion and settling velocities of mollusc shell debris: Influence of faunal composition

et al. 2018

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Bioclastic particles derived from mollusc shell debris can represent a significant fraction of sandy to gravelly sediments in temperate and cool-water regions with high carbonate productivity. Their reworking and subsequent transport and deposition by waves and currents is highly dependent on the shape and density of the particles. In this study, the hydrodynamic behaviour of shell debris produced by eight mollusc species is investigated for several grain sizes in terms of settling velocity (measurements in a settling tube) and threshold of motion under unidirectional current (flume experiments using an acoustic profiler). Consistent interspecific differences in settling velocity and critical bed shear stress are found, related to differences in shell density, shell structure imaged by scanning electron microscopy and grain shape. Drag coefficients are proposed for each mollusc species, based on an interpolation of settling velocity data. Depending on the shell species, the critical bed shear stress values obtained for bioclastic particles fall within or slightly below empirical envelopes established for siliciclastic particles, despite very low settling velocity values. The results suggest that settling velocity, often used to describe the entrainment of sediment particles through the equivalent diameter, is not a suitable parameter to predict the initiation of motion of shell debris. The influence of the flat shape of bioclastic particles on the initiation of motion under oscillatory flows and during bedload and saltation transport is yet to be elucidated.

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Settling Velocity and Grain Shape of Maerl Biogenic Gravel

Cited by 17 publications

References 32 publications

Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plumes in the Clarion Clipperton Fracture Zone (eastern-central Pacific)

Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plumes in the Clarion Clipperton Fracture Zone (eastern-central Pacific)

Blue carbon: past, present and future, with emphasis on macroalgae

Threshold of motion and settling velocities of mollusc shell debris: Influence of faunal composition

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