Particle sinking rates

Particle sinking rates are of considerable interest because the fester a particle can make the trip to the seafloor, the shorter the time it is subject to decomposition or dissolution and, hence, the greater its chances for burial in the sediments. The length of the trip is dictated by the depth to the seafloor, the horizontal current velocity, and the particle sinking rates. As shown in Figure 13.5, sedimentation rates decrease with increasing water depth. This relationship reflects the preservation issue and the feet that coastal waters tend to have larger sources of particles to the surfece zone. 

Some particles, particularly the biogenous ones, are prone to alteration as they settle onto the sediments and then imdergo burial. The likelihood of particle preservation is generally enhanced in settings where the trip to the seafloor is short and burial rates are fast. The time a particle takes to settle onto the seafloor is determined by water depth and particle sinking rates. The latter is a function of particle shape and density. Seawater... 

The variation of the respiration rate with depth in the ocean depends strongly on factors controlling organic matter degradation and particle sinking rates. The role of mineral content (CaCOs and... 

Many particles reach the seafloor by sinking through the water column. This particle-byparticle accumulation is termed pelagic sedimentation. Sinking rates depend on particle size, shape, and density. The sinking rate of a particle in a fluid experiencing laminar flow can be estimated from Ostwald s modification of Stokes law. 

Thus, for particles with a similar density and shape, sinking rates increase with increasing diameter because of the decrease in surface area to volume ratio. As shown in Table 13-5, sand-sized grains reach the sediments in a few days, whereas clays can take centuries. If entrained in a current, sinking particles can also experience significant horizontal transport. 

Particle Type Particle Diameter (micron) or Source Sinking Rate Time to Settle through 4 km Water Depth Horizontal Distance (km) Traveled in Sinking 1000 m through a Current of Icm/s Reference... 

Away from the influence of the continents, the %CaC03 in the sediments is largely controlled by the processes that determine whether sinking detrital calcium carbonate survives the trip to the seafloor. Some of these processes are related to the thermodynamic controls on calciiun carbonate solubility and others are a consequence of the relative rates of particle sinking and dissolution. 

Particle ballasting Packaging of particles which enhances their sinking rates and also appears to confer some protection against microbial attack. 

Figure 6.3 The sinking rates for particles (<100 pm) that follow Stokes law and for particles typically greater than 0.1 to 0.2 mm in diameter settling velocity varies according to the square root of the diameter—as described by the impact law. (Modified from Krumbein and Sloss, 1963.)...

Next the difficulties in obtaining a good description of the particle electrode interaction are noticed. For non-electrochemical systems several particle surface interaction models exist of which the perfect sink , that is all particles arriving within a critical distance of the electrode are captured, is the simplest one. However, the perfect sink condition can not be used, because it predicts a continuous increase in particle codeposition with increasing current density, which contradicts experimental observations. Therefore, an interaction model based on the assumption that the reduction of adsorbed ions is the determining factor for particle deposition is proposed. This electrode-ion-particle electron transfer (EIPET) model leads to a Butler-Volmer like expression for the particle deposition rate ... 

Particle aggregation effects can also be parameterized in explicit formulations by making the sinking rate of the detritus a function of detritus concentration. For example. Hood et al. (2003) applied this kind of simple parameterization in an NPZD model to account for aggregation that can occur in diatom blooms. In their model phytoplankton sink at the rate... 

Sinking rates of solitary phytoplankton cells are only about a meter per day (Smayda, 1970). Particles that sink this slowly require over a year to reach the benthos of the relatively shallow continental shelf, and ten years to reach the abyssal ocean floor. Given the rapid rates of microbial decomposition of organic material in the ocean and the abundance of zooplankton grazers, it is virtually impossible for such a slowly sinking particle to reach the seafloor. 

In this model S represents the average sinking rate of the population of small, slowly settling particles that contain most of the inventory of particulate thorium in the ocean. According to this model, particulate Th lost from the system (kiAjh) is removed permanently. Subsequent studies have shown this latter condition not to be... 

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